Welcome to Retro, my personal take on the Forth language. This is a modern system primarily targeting desktop, mobile, and servers, though it can also be used on some larger (ARM, MIPS32) embedded systems.

The language is Forth. It is untyped, uses a stack to pass data between functions called words, and a dictionary which tracks the word names and data structures.

But it's not a traditional Forth. Retro draws influences from many sources and takes a unique approach to the language.

Retro has a large vocabulary of words. Keeping a copy of the Glossary on hand is highly recommended as you learn to use Retro.

This book will hopefully help you develop a better understanding of Retro and how it works.

I periodically make stable releases. This will typically happen quarterly.

• http://forthworks.com/retro
• http://forth.works

Snapshots

A lot of development happens between releases. I make snapshots of my working source tree nightly (and often more often).

The latest snapshot can be downloaded from the following stable URLs:

• http://forthworks.com/retro/r/latest.tar.gz
• gopher://forthworks.com/9/retro/r/latest.tar.gz

I use a Fossil repository to manage development. To obtain a copy of the repository install Fossil and:

fossil clone http://forthworks.com:8000 retro.fossil mkdir retro cd retro fossil open /path/to/retro.fossil

See the Fossil documentation for details on using Fossil to keep your local copy of the repository current.

This will let you stay current with my latest changes faster than the snapshots, but you may occasionally encounter bigger problems as some commits may be in a partially broken state.

If you have problems, check the version of Fossil you are using. I am currently using Fossil 2.10, you may experience issues checking out or cloning if using older versions.

There is now a read-only mirror of the fossil repository provided via git. This is hosted on sr.ht.

git clone https://git.sr.ht/~crc_/retroforth

Notes

I personally recommend using either a recent snapshot or a build from one of the repositories. This will reflect the latest system as I use it, and are normally reliable as I run them daily for my production systems.

Retro is well supported on BSD (tested on FreeBSD, NetBSD, OpenBSD), Linux, and macOS systems. It should build on any of these without issue.

Requirements

• c compiler & linker
• standard headers
• make

Process

For a standard 32-bit system:

Run make

This will build the toolchain and then the main retro executable.

Executables

In the bin/ directory, you should see the following:

retro retro-unu retro-muri retro-extend retro-embedimage retro-describe

You can conduct a quick test of the build by running bin/retro:

./bin/retro

Exit by typing bye and pressing enter.

Installation

You can install Retro globally on BSD systems (and possibly Linux) by doing:

doas make install

or:

sudo make install

Linux

To build on Linux, you need to link with libdl if using the optional FFI. To do this, edit the GNUmakefile and uncomment this before building:

# LIBDL += -ldl

Haiku

To build on Haiku, you need to link with the network library if using sockets. E.g.:

make LDFLAGS=-lnetwork

Issues

If you run into any build issues, please send details to crc@forth.works so I can work on addressing them as quickly as possible.

It is possible to build Retro on Windows, though a few of the extensions are not supported:

• no unix: words
• no gopher: words

This is currently more difficult than on a Unix host. If you have Windows 10 and WSL, it may be better to build under that (using the Unix instructions).

Retro on Windows is built with TCC.

Go to http://download.savannah.gnu.org/releases/tinycc/

Download the winapi-full and tcc-xxxx-bin packages for your system. Decompress them, copy the headers from the winapi package into the tcc directory.

Copy the vm/nga-c/retro.c and the vm/nga-c/image.c to the directory you setup tcc into.

Build

Building will require use of the command line. Assuming that tcc.exe is in the current directory along with the Retro sources:

tcc retro.c -o retro.exe

In addition to the C implementation, there are a few other interfaces that can be built.

Requirements

• c compiler (tested: clang, tcc, gcc)
• make
• standard unix shell

retro-repl

A basic interactive system can be built by using:

make bin/retro-repl

This requires a copy of ngaImage to be in the current directory.

Barebones

This is a minimal version of the retro-repl. It keeps the C portion as short as possible, making it a useful starting point for new interfaces.

To build:

make bin/retro-barebones

retro-compiler

This is a turnkey compiler. It can compile a new executable bundling a Retro VM and image.

Requirements:

• BSD or Linux
• objcopy in $PATH

To build:

make bin/retro-compiler

Example use:

1. Given a source file like "Hello.forth":

~~~ :hello 'hello_world! s:put nl ; ~~~

2. Use:

./bin/retro-compiler Hello.forth hello

The first argument is the source file, the second is the word to run on startup.

3. Run the generated a.out

Limits:

This only supports the core words ('all' interface) and the file i/o words. Support for other I/O extensions will be added in the future.

Pascal

There is a Pascal version of retro-repl.

Dependencies:

• freepascal

Building:

cd vm/nga-pascal fpc listener.lpr

This will require a copy of the ngaImage in the current directory.

This is an implementation of retro-repl in Python. As with retro-repl it requires the ngaImage in the current directory when starting.

This is an implementation of retro-repl in C#. As with retro-repl it requires the ngaImage in the current directory when starting.

Building:

cd vm\nga-csharp csc retro.cs

You'll need to make sure your path has the CSC.EXE in it, or provide a full path to it. Something like this should reveal the path to use:

dir /s %WINDIR%\CSC.EXE

I've only tested building this using Microsoft's .NET tools. It should also build and run under Mono.

While a simple make will suffice for building Retro, there are a number of ways to customize the build to your needs.

In this chapter, replace Makefile with GNUmakefile if you are using GNU Make (most Linux and macOS users will probably be using this).

Many of the I/O devices are optional. The most common ones are enabled by default in the Makefile. Look near the end of the top section for lines starting with ENABLED:

ENABLED ?= ENABLED += -DENABLE_FLOATS ENABLED += -DENABLE_FILES ENABLED += -DENABLE_UNIX ENABLED += -DENABLE_RNG ENABLED += -DENABLE_CLOCK ENABLED += -DENABLE_SCRIPTING ENABLED += -DENABLE_SIGNALS # ENABLED += -DENABLE_SOCKETS # ENABLED += -DENABLE_MULTICORE ENABLED += -DENABLE_FFI

Lines starting with a # are commented out and will not be processed when building. Here you can easily enable or disable specific devices in the VM.

You should also remove any disabled devices from the DEVICES ?= lines if you want to exclude the Forth part of them from the image.

Note: on platforms (like Linux) that lack the strl* functions from libc, make sure the ENABLED += -DNEEDS_STRL is not commented out.

For the FFI, on Linux, you will need to link with libdl. Edit the GNUmakefile to uncomment the # LIBDL += -ldl line.

If you want to build with sockets support, uncomment the # ENABLED += -DENABLE_SOCKETS and DEVICES += interface/sockets.retro lines before building.

You may need or want to adjust the compiler flags. In the first section of the Makefile, look for CFLAGS and add/change as desired to override the defaults.

64-Bit

A standard Retro system uses a 32-bit word size. You can increase this to 64-bit though. For a one-off build:

make OPTIONS=-DBIT64

You can alter the stack sizes by defining STACK_DEPTH and ADDRESSES. For a one-off build with a max stack depth of 4000 items and 500 addresses on the return stack:

make OPTIONS="-DSTACK_DEPTH=4000 -DADDRESSES=500

You can also alter the image size. Again, for a one-off build:

make OPTIONS=-DIMAGE_SIZE=4000000

Would build a system with a maximum image size of 4,000,000 cells.

If you do any of these routinely, edit the Makefile to include them.

OPTIONS ?= OPTIONS += -DBIT64 OPTIONS += -DSTACK_DEPTH=4000 OPTIONS += -DADDRESSES=500 OPTIONS += -DIMAGE_SIZE=4000000

You can customize the image further by having the build process include your code in the image.

In the top level directory is a package directory containing a file named list.forth. You can add files to compile into your system by adding them to the list.forth and rebuilding.

Example:

If you have wanted to include the NumbersWithoutPrefixes.forth example, add:

~~~ 'example/NumbersWithoutPrefixes.forth include ~~~

To the start of the list.forth file and then run make again.

If you have an existing Retro build and want to have the system handle loading extensions with less manual intervention by putting the source files in package/extensions and running make update-extensions

After rebuilding, the newly built bin/retro will now include your additions.

Retro can be run for scripting or interactive use.

Interactive

To start it interactively, run: retro without any command line arguments, or with -i.

Starting the interactive system:

```
retro
```

Or:

```
retro -i
```

This should be sufficient for most uses.

Retro will work with piped input.

E.g.,

```
echo "'lol s:put nl" | retro
```

You can run code in a file very easily. This is simply:

```
retro filename
```

You can follow the filename with any arguments that it may need. These will be accessible to the program via the script:arguments and script:get-argument words.

Source files must be written in Unu format.

Scripting

You can use Retro to write scripts. Add a shebang:

```
#!/usr/bin/env retro
```

And make the file executable.

Source files must be written in Unu format.

For a summary of the full command line arguments available:

Scripting Usage:

    retro filename [script arguments...]

Interactive Usage:

    retro [-h] [-i] [-f filename] [-t]

  -h           Display this help text   -i           Interactive mode (line buffered)   -f filename  Run the contents of the specified file   -t           Run tests (in ``` blocks) in any loaded files

Start Retro in interactive mode:

```
retro -i
```

You should see something similar to this:

Retro 12 (2021.7) 8388608 MAX, TIB @ 1025, Heap @ 9374

At this point you are at the listener, which reads and processes your input. You are now set to begin exploring Retro.

Retro is normally silent; unlike other Forth systems, it does not display an "ok" prompt.

To exit, run bye:

```
bye
```

Retro is written in a literate style. Most of the sources are in a format called Unu. This allows easy mixing of commentary and code blocks, making it simple to document the code.

As an example,

# Determine The Average Word Name Length

To determine the average length of a word name two values are needed. First, the total length of all names in the Dictionary:

~~~ #0 [ d:name s:length + ] d:for-each ~~~

And then the number of words in the Dictionary:

~~~ #0 [ drop n:inc ] d:for-each ~~~

With these, a simple division is all that's left.

~~~ / ~~~

Finally, display the results:

~~~ 'Average_name_length:_%n\n s:format s:put ~~~

This illustrates the format. Only code in the fenced blocks (between ~~~ pairs) get extracted and run.

(Note: this only applies to source files; fences are not used when entering code interactively).

The name Unu comes from the Maori language, where it means:

(verb) (-hia) pull out, withdraw, draw out, extract. Taken from https://maoridictionary.co.nz/

I use a variation of Markdown for writing documentation and when commenting code written in Retro. The syntax is described below.

Headings

Headings start with one or more number (#) signs. The number of number signs should correspond to the heading level.

# Heading 1 ## Heading 2 ### Heading 3 #### Heading 4

My Markdown does not support the alternate underline format for headings.

To create paragraphs, use a blank line to separate one or more lines of text.

Do not add spaces or tabs at the start of a paragraph as this may cause the Markdown tools to interpret the line improperly.

Line breaks are entered at the end of each line.

Emphasis

Bold

To make text bold, surround it with asterisks.

The *bold* word.

Italic

To make text italic, surround it with front slashes.

The /italic words/.

Underline

To underline text, surround it with underscores.

Underline _some text_.

Horizontal rules can be inserted by starting a line with a sequence of four or more dashes (-) or four or more alternating dash and plus (-+-+) characters.

----

Lists

Lists start with a - or *, followed by a space, then the item text. Additionally, nested lists starting with two spaces before the list marker can be used.

- this is a list item - so is this

  - this will be indented   - likewise

- back to the standard level

Code

Code blocks start and end with ~~~ on a line by themselves.

Sum the values.

~~~ { #10 #20 #13 #4 #22 } #0 [ + ] a:reduce ~~~

You can also denote code by starting the line with four spaces.

    This line will be treated as code.

Unit testing blocks start and end with on a line by themselves.

``` { #10 #20 #13 #4 #22 } #0 [ + ] a:reduce ```

To mark a sequence as inline code, surround it with backticks.

For instance, look at the value in `Compiler` to see if the colon compiler is active.

Escaping

You can preceed a character with a backslash () to have it not be processed as a Markdown element.

Programming in Retro is all about creating words to solve the problem at hand. Words operate on data, which can be kept in memory or on the stack.

Let's look at this by solving a small problem: writing a word to determine if a string is a palindrome.

A palindrome is a phrase which reads the same backward and forward.

We first need a string to look at. Starting with something easy:

```
'anna
```

Looking in the Glossary, there is a s:reverse word for reversing a string. We can find dup to copy a value, and s:eq? to compare two strings. So testing:

```
'anna dup s:reverse s:eq?
```

This yields -1 (TRUE) as expected. So we can easily name it:

```
:palindrome? dup s:reverse s:eq? ;
```

Naming uses the : sigil to add a new word to the dictionary. The words that make up the definition are then placed, with a final word (;) ending the definition. We can then use this:

```
'anna palindrome?
```

Once defined there is no difference between our new word and any of the words already provided by the Retro system.

Syntax

Retro has more syntax than a traditional Forth due to ideas borrowed from ColorForth and some design decisions. This has some useful traits, and helps to make the language more consistent.

Tokens

Input is divided into a series of whitespace delimited tokens. Each of these is then processed individually. There are no parsing words in Retro.

Tokens may have a single character sigil, which Retro will use to decide how to process the token.

Sigils

Sigils are single characters added to the start of a token to guide the compiler. The use of these is a major way in which Retro differs from traditional Forth.

When a token is passed to interpret, Retro first takes the initial character and looks to see if there is a word that matches this. If so, it will pass the rest of the token to that word to handle.

In a traditional Forth, the interpret process is something like:

get token is token in the dictionary?   yes:     is it immediate?       yes: call the word.       no:  are we interpreting?            yes: call the word            no:  compile a call to the word   no:     is it a number?       yes: are we interpreting?            yes: push the number to the stack            no:  compile the number as a literal       no:  report an error ("not found")

In Retro, the interpret process is basically:

get token does the first character match a `sigil:` word?   yes: pass the token to the sigil handler   no:  is token a word in the dictionary?        yes: push the XT to the stack and call the             class handler        no:  report an error ("not found")

All of the actual logic for how to deal with tokens is moved to the individual sigil handlers, and the logic for handling words is moved to word class handlers.

This means that sigils are used for a lot of things. Numbers? Handled by a # sigil. Strings? Use the ' sigil. Comments? Use (. Making a new word? Use the : sigil.

The major sigils are:

| Sigil  | Used For                      | | ------ | ----------------------------- | | @      | Fetch from variable           | | !      | Store into variable           | | &      | Pointer to named item         | | #      | Numbers                       | | $      | ASCII characters              | | '      | Strings                       | | (      | Comments                      | | :      | Define a word                 |

The individual sigils will be covered in more detail in the later chapters on working with different data types.

Word classes are words which take a pointer and do something with it. These are covered in detail in their own chapter, but essentially they decide how to execute or compile specific types of words.

In addition to the core retro binary, the bin directory will contain a few other tools.

retro

This is the main RETRO binary.

retro-describe

This is a program that looks up entries in the Glossary.

At the command line, you can use it like:

retro-describe s:for-each

You can pass multiple word names to it:

retro-describe s:for-each nl d:words

retro-embedimage

This is a program which generates a C file with the ngaImage contents. It's used when building retro.

retro-embedimage ngaImage

The output is written to stdout; redirect it as needed.

retro-extend

This is a program which compiles code into the ngaImage. It's used when building retro and when you want to make a standalone image with custom additions.

Example command line:

retro-extend ngaImage example/rot13.forth

Pass the image name as the first argument, and then file names as subsequent ones. Do not use this for things relying on I/O apart from the basic console output as it doesn't emulate other devices. If you need to load in things that rely on using the optional I/O devices, see the Advanced Builds chapter.

retro-muri

This is the assembler for Nga. It's used to build the initial RETRO kernel and can be used by other tools as well.

retro-muri retro.muri

These tools are intended to be used together. The first tool, retro-tags, will recursively scan the current directory for RETRO source files and extract the locations of words defined in them. These will be written to disk in a tags file, using the standard ctags format.

retro-locate takes a word name, and returns the location(s) where it is defined. This requires a tags file to be present.

Create the tags file:

retro-tags

Locate a word:

retro-locate n:square

retro-unu

This is the literate source extraction tool for RETRO. It is used in building retro.

Example usage:

retro-unu literate/RetroForth.md

Output is written to stdout; redirect as neeeded.

In addition to the base system, users of RETRO on Unix hosts with ELF executables can build and use the retro-compiler to generate turnkey executables.

Requirements

• Unix host
• ELF executable support
• objcopy in the $PATH

Building

make bin/retro-compiler

Installing

Copy bin/retro-compiler to somewhere in your $PATH.

Using

retro-compiler takes two arguments: the source file to compile and the name of the word to use as the main entry point.

Example:

Given a hello.forth:

~~~ :hello 'Hello_World! s:put nl ; ~~~

Use:

retro-compiler hello.forth hello

The compiler will generate an a.out file which you can then rename.

This does not provide the scripting support for command line arguments that the standard retro interface offers.

A copy of objcopy needs to be in the path for compilation to work.

The current working directory must be writable.

This only supports hosts using ELF executables.

The output file name is fixed to a.out.

RETRO(1) General Commands Manual RETRO(1)

RETRO  retro - a modern, pragmatic forth development system

SYNOPSIS  retro [-h] [-i] [-t] [-f filename] [-u filename] [-r filename] [filename script-args]

DESCRIPTION  RETRO is a modern, pragmatic Forth drawing influences from many sources.  It's clean, elegant, tiny, and easy to grasp and adapt to various uses.

 retro is the main interface for interacting with Retro. It provides both  an interactive and a scripting  model.

OPTIONS  -h       Display a help screen.

 -i       Start Retro in interactive mode.

 -s       Start Retro in interactive mode and supress the startup message.

 -t       Run any test blocks in the loaded files.

 -f filename Run any code blocks in the specified file.

 -u filename Load and use the specified image file rather than the integral one.

 -r filename Load and run the code in the specified image file rather than the integral one.

 filename script-args Run code blocks in a single file. Pass script-args to the code being run.

AUTHORS  Charles Childers <crc@forthworks.com>

OpenBSD 6.4 September 2019 OpenBSD 6.4

RETRO-DESCRIBE(1) General Commands Manual RETRO-DESCRIBE(1)

RETRO-DESCRIBE  retro-describe - a modern, pragmatic forth development system

SYNOPSIS  retro-describe wordname [additional wordnames]

DESCRIPTION  RETRO is a modern, pragmatic Forth drawing influences from many sources.  It's clean, elegant, tiny, and easy to grasp and adapt to various uses.

 retro-describe is a tool for looking up the description and stack  comments for words in the core language and extensions.  It will write  output to stdout.

AUTHORS  Charles Childers <crc@forthworks.com>

OpenBSD 6.4 May 2019 OpenBSD 6.4

RETRO-DOCUMENT(1) General Commands Manual RETRO-DOCUMENT(1)

RETRO-DOCUMENT  retro-document - a modern, pragmatic forth development system

SYNOPSIS  retro-document filename

DESCRIPTION  RETRO is a modern, pragmatic Forth drawing influences from many sources.  It's clean, elegant, tiny, and easy to grasp and adapt to various uses.

 retro-document is a tool for generating a listing of the descriptions and  stack comments for all standard word used in a source file. It will write  output to stdout.

AUTHORS  Charles Childers <crc@forthworks.com>

OpenBSD 6.4 May 2019 OpenBSD 6.4

RETRO-EMBEDIMAGE(1) General Commands Manual RETRO-EMBEDIMAGE(1)

RETRO-EMBEDIMAGE  retro-embedimage - a modern, pragmatic forth development system

SYNOPSIS  retro-embedimage [filename]

DESCRIPTION  RETRO is a modern, pragmatic Forth drawing influences from many sources.  It's clean, elegant, tiny, and easy to grasp and adapt to various uses.

 retro-embedimage loads the specified image (or `ngaImage` from the  current directory if none is specified). It converts this into C code  that can be compiled for inclusion in a RETRO executable. It will write  the output to stdout.

AUTHORS  Charles Childers <crc@forthworks.com>

OpenBSD 6.4 February 2019 OpenBSD 6.4

RETRO-EXTEND(1) General Commands Manual RETRO-EXTEND(1)

RETRO-EXTEND  retro-extend - a modern, pragmatic forth development system

SYNOPSIS  retro-extend image filename [filenames]

DESCRIPTION  RETRO is a modern, pragmatic Forth drawing influences from many sources.  It's clean, elegant, tiny, and easy to grasp and adapt to various uses.

 retro-extend is a tool to load additional code into an image file. It  takes the name of an image file and one or more source files to load into  the image. After completion the image file will be updated with the  changes.

CAVEATS  retro-extend only emulates the minimal console output device. If the  source files require additional I/O to be present, the extend process  will likely fail to work correctly.

AUTHORS  Charles Childers <crc@forthworks.com>

OpenBSD 6.4 January 2021 OpenBSD 6.4

RETRO-LOCATE(1) General Commands Manual RETRO-LOCATE(1)

RETRO-LOCATE  retro-locate - a modern, pragmatic forth development system

SYNOPSIS  retro-locate wordname

DESCRIPTION  RETRO is a modern, pragmatic Forth drawing influences from many sources.  It's clean, elegant, tiny, and easy to grasp and adapt to various uses.

 retro-locate searches the tags file generated by retro-tags for the  desired word name. Any matches are displayed, along with the line number.

AUTHORS  Charles Childers <crc@forthworks.com>

OpenBSD 6.6 January 2020 OpenBSD 6.6

RETRO-MURI(1) General Commands Manual RETRO-MURI(1)

RETRO-MURI  retro-muri - a modern, pragmatic forth development system

SYNOPSIS  retro-muri filename

DESCRIPTION  RETRO is a modern, pragmatic Forth drawing influences from many sources.  It's clean, elegant, tiny, and easy to grasp and adapt to various uses.

 retro-muri is an assembler for Nga, the virtual machine at the heart of  Retro. It is used to build the image file containing the actual Retro  language.

 This will extract the code blocks in the specified file and generate an  image file named `ngaImage`.

AUTHORS  Charles Childers <crc@forthworks.com>

OpenBSD 6.4 February 2019 OpenBSD 6.4

RETRO-TAGS(1) General Commands Manual RETRO-TAGS(1)

RETRO-TAGS  retro-tags - a modern, pragmatic forth development system

SYNOPSIS  retro-tags

DESCRIPTION  RETRO is a modern, pragmatic Forth drawing influences from many sources.  It's clean, elegant, tiny, and easy to grasp and adapt to various uses.

 retro-tags is a tool for extracting code from fenced blocks in literate  sources and generating a tags file compatible with ctags.

AUTHORS  Charles Childers <crc@forthworks.com>

OpenBSD 6.4 August 2019 OpenBSD 6.4

Word names in RETRO generally follow the following conventions.

• Readability is important
• Be consistent
• Don't use a sigil as the first character of a name
• Don't use underscores in word names
• Use short names for indices
• Word names start with a - for "not"
• Words returning a flag end in ?

The word names will generally follow a form like:

[namespace:]name

The namespace: is optional, but recommended for consistency with the rest of the system and to make it easier to identify related words.

Case

Word names are lowercase, with a dash (-) for compound names.

hello drop-pair s:for-each

Variables use TitleCase, with no dash between compound names.

Base Heap StringBuffers

Constants are UPPERCASE, with a dash (-) for compound names.

TRUE FALSE f:PI MAX-STRING-LENGTH

Namespaces

Words are grouped into broad namespaces by attaching a short prefix string to the start of a name.

The common namespaces are:

| Prefix  | Contains                                               | | ------- | ------------------------------------------------------ | | a:      | Words operating on simple arrays                       | | ASCII:  | ASCII character constants for control characters       | | buffer: | Words for operating on a simple linear LIFO buffer     | | c:      | Words for operating on ASCII character data            | | class:  | Contains class handlers for words                      | | d:      | Words operating on the Dictionary                      | | err:    | Words for handling errors                              | | io:     | General I/O words                                      | | n:      | Words operating on numeric data                        | | sigil:  | Contains sigil handlers                                | | s:      | Words operating on string data                         | | v:      | Words operating on variables                           | | file:   | File I/O words                                         | | f:      | Floating Point words                                   | | unix:   | Unix system call words                                 |

Tips

Avoid using a sigil as the first character of a word name. RETRO will look for sigils first, this will prevent direct use of the work in question.

To find a list of sigil characters, do:

'sigil: d:words-with

Underscores in strings are replaced by spaces. This is problematic, especially with variables. Consider:

'test_name var #188 !test_name

In this, the string for the name is converted to "test name". The store in the second line will not add the space, so resolves to an incorrect address.

I personally recommend avoiding the use of underscores in any word names.

RETRO has two stacks. The primary one is used to pass data between words. The second one primarily holds return addresses.

Each time a word is called, the next address is pushed to the return stack.

Most words in RETRO have a stack comment. These look like:

(-) (nn-n)

As with all comments, a stack comment begins with ( and should end with a ). There are two parts to the comment. On the left side of the - is what the word consumes. On the right is what it leaves.

RETRO uses a short notation, with one character per value taken or left. In general, the following symbols represent certain types of values.

| Notation            | Represents              | | ------------------- | ----------------------- | | b, n, m, o, x, y, z | generic numeric values  | | s                   | string                  | | v                   | variable                | | p, a                | pointers                | | q                   | quotation               | | d                   | dictionary header       | | f                   | `TRUE` or `FALSE` flag. |

In the case of something like (xyz-m), RETRO expects z to be on the top of the stack, with y below it and x below the y value. And after execution, a single value (m) will be left on the stack.

Words with no stack effect have a comment of (-)

For combinators (words consuming quotations), you can include a sub-comment indicating the expected stack effect of the quote. E.g.,

(q(-f)-)

Indicates a word consuming a quote and returning nothing. The quote should return a flag.

RETRO offers a number of words for operating on statically sized arrays.

Namespace

The words operating on arrays are kept in an a: namespace.

The easiest way to create an array is to wrap the values in a { and } pair:

```
{ #1 #2 #3 #4 }
{ 'this 'is 'an 'array 'of 'strings }
{ 'this 'is 'a 'mixed 'array #1 #2 #3 }
```

You can also make an array from a quotation which returns values and the number of values to store in the a:

```
[ #1 #2 #3  #3 ] a:counted-results
[ #1 #2 #3  #3 ] a:make
```

You can access a specific value with a:th and fetch or store:

```
{ #1 #2 #3 #4 } #3 a:th fetch
```

Use a:length to find the size of the array.

```
{ #1 #2 #3 #4 } a:length
```

Duplicate

Use a:dup to make a copy of an a:

```
{ #1 #2 #3 #4 } a:dup
```

Filtering

RETRO provides a:filter which extracts matching values from an array. This is used like:

```
{ #1 #2 #3 #4 #5 #6 #7 #8 } [ n:even? ] a:filter
```

The quote will be passed each value in the array and should return TRUE or FALSE. Values that lead to TRUE will be collected into a new array.

Mapping

a:map applies a quotation to each item in an array and constructs a new array from the returned values.

Example:

```
{ #1 #2 #3 } [ #10 * ] a:map
```

Reduce

a:reduce takes an array, a starting value, and a quote. It executes the quote once for each item in the array, passing the item and the value to the quote. The quote should consume both and return a new value.

```
{ #1 #2 #3 } #0 [ + ] a:reduce
```

Search

RETRO provides a:contains? and a:contains/string? to search an array for a value (either a number or string) and return either TRUE or FALSE.

```
#100  { #1 #2 #3 } a:contains?
'test { 'abc 'def 'test 'ghi } a:contains/string?
```

Implementation

In memory, an array is a count followed by the values. As an example, if you have an array:

{ #10 #20 #30 }

In memory this would be setup as:

| Offset | Value | | ------ | ----- | | 000    | 3     | | 001    | 10    | | 002    | 20    | | 003    | 30    |

You can construct one on the fly by keeping a pointer to here and using , to place the values. E.g.,

here [ #3 , #10 , #20 , #30 , ] dip

An example of this can be seen in this excerpt from an example (example/Primes.forth):

:create-set (-a)      here #3000 , #2 #3002 [ dup , n:inc ] times drop ;

RETRO runs on a virtual machine called Nga. It provides a standard assembler for this called Muri.

Muri is a simple, multipass model that's not fancy, but suffices for RETRO's needs.

A small example (test.muri)

~~~ i liju.... r main : c:put i liiire.. i 0 : main i lilica.. d 97 i liju.... r main ~~~

Assembling it:

retro-muri test.muri

So breaking down: Muri extracts the assembly code blocks to assemble, then proceeds to do the assembly. Each source line starts with a directive, followed by a space, and then ending with a value.

The directives are:

:    value is a label i    value is an instruction bundle d    value is a numeric value r    value is a reference s    value is a string to inline

Instructions for Nga are provided as bundles. Each memory location can store up to four instructions. And each instruction gets a two character identifier.

From the list of instructions:

0 nop   5 push  10 ret   15 fetch 20 div   25 zret 1 lit   6 pop   11 eq    16 store 21 and   26 halt 2 dup   7 jump  12 neq   17 add   22 or    27 ienum 3 drop  8 call  13 lt    18 sub   23 xor   28 iquery 4 swap  9 ccall 14 gt    19 mul   24 shift 29 iinvoke

This reduces to:

0 ..    5 pu    10 re    15 fe    20 di    25 zr 1 li    6 po    11 eq    16 st    21 an    26 ha 2 du    7 ju    12 ne    17 ad    22 or    27 ie 3 dr    8 ca    13 lt    18 su    23 xo    28 iq 4 sw    9 cc    14 gt    19 mu    24 sh    29 ii

Most are just the first two letters of the instruction name. I use .. instead of no for NOP, and the first letter of each I/O instruction name. So a bundle may look like:

dumure..

(This would correspond to dup multiply return nop).

RETRO also has a runtime variation of Muri that can be used when you need to generate more optimal code. So one can write:

:n:square dup * ;

Or:

:n:square \dumure.. ;

The second one will be faster, as the entire definition is one bundle, which reduces memory reads and decoding by 2/3.

Doing this is less readable, so I only recommend doing so after you have finalized working RETRO level code and determined the best places to optimize.

The runtime assembler has the following directives:

i    value is an instruction bundle d    value is a numeric value r    value is a reference

Additionally, in the runtime assembler, these are reversed:

'dudumu.. i

Instead of:

i dudumu..

The runtime assembler also provides three sigils for use in inlining machine code into a definition. These are:

 \    Treat token as an assembly sequence  `    Treat token as a numeric value  ^    Treat token as a reference

E.g., instead of doing something like:

:n:square as{ 'dumu.... i }as ; :test as{ 'lilica.... i #22 d 'n:square r }as ;

Just write:

:n:square \dumu.... ; :test     \lilica.. `22 ^n:square ; 

RETRO provides words for operating on a linear memory area. This can be useful in building strings or custom data structures.

Namespace

Words operating on the buffer are kept in the buffer: namespace.

Implementation

A buffer is a linear sequence of memory. The buffer words provide a means of incrementally storing and retrieving values from it.

The buffer words keep track of the start and end of the buffer. They also ensure that an ASCII:NULL is written after the last value, which make using them for string data easy.

Limitations

Only one buffer can be active at a time. RETRO provides a buffer:preserve combinator to allow using a second one before returning to the prior one.

To set a buffer as the active one use buffer:set. This takes an address.

The buffer will be assumed to be empty. The initial value will be set to ASCII:NULL.

Use buffer:add to append a value to the buffer. This takes a single value and will also add an ASCII:NULL after the end of the buffer.

To return the last value in the buffer you can use buffer:get. This removes the value and sets an ASCII:NULL in the memory location the returned value occupied.

RETRO provides buffer:start to get the initial address in the buffer, buffer:end to get the last address (ignoring the ASCII:NULL), and buffer:size to return the number of values in the buffer.

Reset

You can reset a buffer to the empty state using buffer:empty.

Example

To begin, create a memory region to use as a buffer.

```
'Test d:create #1025 allot
```

Then you can set this as the current buffer:

```
&Test buffer:set
```

When a buffer is set, the vocabulary sets an internal index to the first address in it. This will be incremented when you add data and decremented when you remove data.

Let's add some stuff using buffer:add:

```
#100 buffer:add
#200 buffer:add
#300 buffer:add
```

And then retrieve the values:

```
buffer:get n:put nl
buffer:get n:put nl
buffer:get n:put nl
```

You can remove all values using buffer:empty:

```
#100 buffer:add
#200 buffer:add
#300 buffer:add
buffer:empty
```

And ask the buffer how many items it contains:

```
buffer:size n:put nl
#100 buffer:add
#200 buffer:add
#300 buffer:add
buffer:size n:put nl
buffer:empty
```

The other functions are buffer:start, which returns the address of the buffer, buffer:end, which returns the address of the last value, and buffer:preserve. The first is easy to demo:

```
buffer:start Test eq? n:put nl
```

The last one is useful. Only one buffer is ever active at a given time. The buffer:preserve combinator lets you execute a word, saving and restoring the current buffer indexes. So the word could assign and use a new buffer and this will reset the previous one after control returns.

There are a few notes that need to be considered. The preserve combinator saves the start and current index but not the contents. If the word you call uses the same buffer, the contents will remain altered.

Finally, the buffer words have one interesting trait: they store an ASCII NULL after adding each item to the buffer. This lets one use them to build strings easily.

```
Test buffer:set
$h buffer:add
$e buffer:add
$l buffer:add
$l buffer:add
$o buffer:add
$, buffer:add
#32 buffer:add
$w buffer:add
$o buffer:add
$r buffer:add
$l buffer:add
$d buffer:add
buffer:start s:put nl
```

RETRO provides words for working with ASCII characters.

Sigil

Character constants are returned using the $ sigil.

Namespace

Words operating on characters are in the c: namespace.

Classification

RETRO provides a number of words to determine if a character fits into predefined groups.

The primary words for this are:

• c:consonant?
• c:digit?
• c:letter?
• c:lowercase?
• c:uppercase?
• c:visible?
• c:vowel?
• c:whitespace?

There are also corresponding "not" forms:

• c:-consonant?
• c:-digit?
• c:-lowercase?
• c:-uppercase?
• c:-visible?
• c:-vowel?
• c:-whitespace?

All of these take a character and return either a TRUE or FALSE flag.

Conversions

A few words are provided to convert case. Each takes a character and returns the modified character.

• c:to-lower
• c:to-number
• c:to-upper
• c:toggle-case

RETRO also has c:to-string, which takes a character and creates a new temporary string with the character.

I/O

Characters can be displayed using c:put.

```
$a c:put
```

With the default system on BSD, Linux, and macOS (and other Unix style hosts), c:get is provided to read input. This may be buffered, depending on the host.

Words are named functions. To start a word, preceed it's name with a colon. Follow this by the definition, and end with a semicolon.

E.g.,

:do-nothing ; :square dup * ;

The Dictionary is a linked list containing the dictionary headers.

Namespace

Words operating on the dictionary are in the d: namespace.

Variables

Dictionary is a variable holding a pointer to the most recent header.

Each entry follows the following structure:

Offset   Contains ------   --------------------------- 0000     Link to Prior Header 0001     Link to XT 0002     Link to Class Handler 0003     Source Identifier 0004+    Word name (null terminated)

RETRO provides words for accessing the fields in a portable manner. It's recommended to use these to allow for future revision of the header structure.

Given a pointer to a header, you can use d:xt, d:class, and d:name to access the address of each specific field. There is no d:link, as the link will always be the first field.

RETRO provides several words for operating on the most recent header.

d:last returns a pointer to the latest header. d:last.xt will give the contents of the d:xt field for the latest header. There are also d:last.class and d:last.name.

Two words exist for making new headers. The easy one is d:create. This takes a string for the name and makes a new header with the class set to class:data and the XT field pointing to here.

Example:

```
'Base d:create
```

The other is d:add-header. This takes a string, a pointer to the class handler, and a pointer for the XT field and builds a new header using these.

Example:

```
'Base &class:data #10000 d:add-header
```

Searching

RETRO provides two words for searching the dictionary.

d:lookup takes a string and tries to find it in the dictionary. It will return a pointer to the dictionary header or a value of zero if the word was not found.

d:lookup-xt takes a pointer and will return the dictionary header that has this as the d:xt field, or zero if no match is found.

Iteration

You can use the d:for-each combinator to iterate over all entries in the dictionary. For instance, to display the names of all words:

```
[ d:name s:put sp ] d:for-each
```

For each entry, this combinator will push a pointer to the entry to the stack and call the quotation.

Most Forth systems provide WORDS for listing the names of all words in the dictionary. RETRO does as well, but this is named d:words.

This isn't super useful as looking through several hundred names is annoying. RETRO also provides d:words-with to help in filtering the results.

Example:

```
'class: d:words-with
```

Some RETRO systems include support for floating point numbers. When present, this is built over the system libm using the C double type.

Floating point values are typically 64 bit IEEE 754 double precision (1 bit for the sign, 11 bits for the exponent, and the remaining 52 bits for the value), i.e. 15 decimal digits of precision.

Sigil

Floating point numbers start with a .

Examples:

Token Value .1       1.0 .0.5     0.5 .-.4    -0.4 .1.3     1.3

Namespace

Floating point words are in the f: namespace. There is also a related e: namespace for encoded values, which allows storing of floats in standard memory.

Operation

Floating point values exist on a separate stack, and are bigger than the standard memory cells, so can not be directly stored and fetched from memory.

The floating point system also provides an alternate stack that can be used to temporarily store values.

The following words exist for arranging values on the floating point stack. These are direct analogs to the non-prefiexd words for dealing with the data stack.

• f:nip
• f:over
• f:depth
• f:drop
• f:drop-pair
• f:dup
• f:dup-pair
• f:dump-stack
• f:tuck
• f:swap
• f:rot

For the secondary floating point stack, the following words are provided:

• f:push
• f:pop
• f:adepth
• f:dump-astack

Constants

| Name     | Returns           | | -------- | ----------------- | | `f:E`    | Euler's number    | | `f:-INF` | Negative infinity | | `f:INF`  | Positive infinity | | `f:NAN`  | Not a Number      | | `f:PI`   | PI                |

Comparisons

The basic set of comparators are the same as those for operating on integers. These are:

• f:-eq?
• f:between?
• f:eq?
• f:gt?
• f:lt?
• f:negative?
• f:positive?
• f:case

There are also a few additions for comparing to special values like infinity and NaN.

• f:-inf?
• f:inf?
• f:nan?

• f:*
• f:+
• f:-
• f:/
• f:abs
• f:floor
• f:inc
• f:limit
• f:max
• f:min
• f:negate
• f:power
• f:ceiling
• f:dec
• f:log
• f:sqrt
• f:square
• f:round
• f:sign
• f:signed-sqrt
• f:signed-square

Geometry

RETRO provides a small number of words for doing geometric related calculations.

| Word | Returns | | -------- | ------------ | | f:acos | arc cosine | | f:asin | arc sine | | f:atan | arc tangent | | f:cos | cosine | | f:sin | sine | | f:tan | tangent |

By leveraging the encoded value functions, RETRO is able to allow storage of floating point values in memory. This does have a tradeoff in accuracy as the memory cells are considerably smaller than a full floating point size.

You can use f:fetch to fetch a floating point value and f:store to store one.

If you need more precision, try Kiyoshi Yoneda's FloatVar example (example/FloatVar.forth), which includes words to store and retrieve values using multiple cells.

• f:to-number
• f:to-string

I/O

The floating point vocabulary has a single I/O word, f:put, for the display of floating point numbers.

RETRO provides a means of encoding and decoding floating point values into standard integer cells. This is based on the paper "Encoding floating point values to shorter integers" by Kiyoshi Yoneda and Charles Childers.

• f:E1
• f:to-e
• e:-INF
• e:-inf?
• e:INF
• e:MAX
• e:MIN
• e:NAN
• e:clip
• e:inf?
• e:max?
• e:min?
• e:n?
• e:nan?
• e:put
• e:to-f
• e:zero?

On Unix and Windows systems RETRO provides a set of words for working with files. As a pragmatic choice these are mostly modeled after the file functions in libc.

The file words are in the file: namespace.

You can open a file for various operations. The functionality allowed depends on the file access mode. Valid modes in RETRO are:

file:A    Open for appending; file pointer set to end of file file:R    Open for reading; file pointer set to start of file file:R+   Open for reading and writing file:W    Open for writing

To open a file, pass the file name and a file mode to file:open.

'/etc/motd file:R file:open

On a successful open this will return a file handle greater than zero.

Additionally, RETRO provides a few other forms for opening files.

To open a file for reading:

'/etc/motd file:open-for-reading

This will return the size of the file (as NOS) and the file handle (as TOS).

To open a file for writing:

'/tmp/test file:open-for-writing

This returns the file handle.

To open a file for append operations:

'/tmp/test file:open-for-append

As with file:open-for-reading, this returns both the size of the file and the file handle.

To close a file, pass the file handle to file:close.

'/etc/motd file:A file:open file:close

To read a byte from an open file, pass the file handle to the file:read word.

@FID file:read n:put

To read a line from a file, pass the file handle to the word file:read-line.

@FID file:read-line s:put

The line is read into a temporary string buffer. Move the text to a safe place if you aren't using it quickly or if the length of the line is bigger than the size of a temporary string.

To write a byte to a file, pass it and the file handle to file:write.

$h @FID file:write $e @FID file:write $l @FID file:write $l @FID file:write $o @FID file:write

Though cells are 32 or 64 bits in size, only the byte value will be written to the file.

You can delete a file by passing the file name to file:delete.

/tmp/test file:delete

Use file:exists? to detect the existance of a file. Pass it a file name and it will return TRUE if existing or FALSE if it does not.

'/etc/motd file:exists?

This will also return TRUE if the filename is a directory.

Use file:flush to flush the system caches for a file. Pass a file handle to this.

@FID file:flush

You can use file:seek to move the internal file pointer for a given file. Pass this the new location and a file.

#100 @FID file:seek

The location for the file pointer is a fixed offset from the start of the file, not a relative offset.

To find the current value of the file pointer within a file just pass the file handle to file:tell.

@FID file:tell

This returns a number that is the number of bytes into the file that the file pointer is currently at.

Use file:size to return the size of a file. Pass this a file handle and it will return the size of a file, or 0 if empty. If the file is a directory, it returns -1.

@FID file:size

If you want to read an entire file into memory you can use file:slurp. This takes the starting address of a memory region and the name of the file.

here '/etc/motd file:slurp

Take care that the memory buffer is large enough for the file being read or you will run into problems.

If you have a string that you want to write to a file, replacing any existing contents, you can use file:spew. This takes the string to write and a file name.

'hello_world '/tmp/test.txt file:spew

You can easily iterate over each line in a file using the word file:for-each-line. This will take a file name and a quote, read each line into a temporary string, then pass this string to the quote.

'/etc/motd [ s:put nl ] file:for-each-line

Loops

RETRO provides several words for creating loops.

An unconditional loop begins with repeat and ends with again.

:test repeat #1 n:put sp again ; test

Unconditional loops must be inside a definition or quote. To exit one of these, use 0;, -if; or if;.

:test #100 repeat 0; dup n:put sp n:dec again ; test

:test #100 repeat dup #50 eq? [ 'done! s:put nl ] if; n:dec again ; test

You can also achieve this via recursion:

:test 0; dup n:put sp n:dec test ; #100 test

Be careful with recursion as the virtual machine will have a limited amount of space for the address stack and recursing too many times can cause a stack overflow.

There are two conditional looping combinators: while and until. Both take a quote and execute it, checking a returned flag to decide when to stop running.

#0 [ dup n:put sp n:inc dup #10 eq? ] until #10 [ dup n:put sp n:dec dup n:-zero? ] while

There are two combinators for counted loops. These are times and indexed-times.

#0 #10 [ dup n:put sp n:inc ] times nl #10 [ I n:put sp ] indexed-times

The indexed-times provides an index via the I, J, and K words. I will be the index of the current loop, with J and K being the indexes of the next two older loops.

The loop indexes can be accessed outside the loop body:

:display I n:square n:put sp ; :squares [ display ] indexed-times nl ; #100 squares

Tradeoffs

The unconditional loop form is more efficient as it's just a simple jump operation. The times counted loops are a little slower, but can be cleaner and more readable in many cases. The indexed-times form is significantly slower than the other two forms.

Numbers in RETRO are signed integers.

Sigil

All numbers start with a # sigil.

Namespace

Most words operating on numbers are in the n: namespace.

A default RETRO system with 32 bit cells provides a range of -2,147,483,648 to 2,147,483,647. For 64 bit systems, the range will be -9,223,372,036,854,775,807 to 9,223,372,036,854,775,806.

You can check the range your VM and image support using:

n:MIN n:MAX

These will return the limits for your system.

Comparisons

RETRO provides a number of comparison words for numeric values.

The basic comparators are:

-eq? eq? lt? lteq? gt? gteq?

Additionally RETRO also provides:

n:-zero? n:between? n:even? n:negative? n:odd? n:positive? n:strictly-positive? n:zero?

+ - * / mod /mod n:abs n:dec n:inc n:limit n:max n:min n:negate n:pow n:sqrt n:square

Conversions

You can convert a number to a string with n:to-string or to a floating point value with n:to-float.

#123 n:to-float  f:put

#123 n:to-string s:put

Display

To display a number, use n:put.

#123 n:put

Sigil

Pointers are returned by the & sigil.

Examples

```
'Base var
&Base fetch
#10 &Base store

#10 &n:inc call
```

Notes

The use of & to get a pointer to a data structure (with a word class of class:data) is not required. I like to use it anyway as it makes my intent a little clearer.

Pointers are useful with combinators. Consider:

```
:abs dup n:negative? [ n:negate ] if ;
```

Since the target quote body is a single word, it is more efficient to use a pointer instead:

```
:abs dup n:negative? &n:negate if ;
```

The advantages are speed (saves a level of call/return by avoiding the quotation) and size (for the same reason). This may be less readable though, so consider the balance of performance to readability when using this approach.

Quotations

Quotes are anonymous functions. RETRO uses these as the basis for executable flow control and combinatorial logic.

To make a quotation, surround the code with square brackets. E.g.,

#1 #2 eq? [ 'No_match s:put nl ] -if

Quotes can be nested:

[ #3 [ #4 ] dip ] call

After creation, a pointer to the quotation is left on the stack (or is compiled into the current definition).

Combinators

Words operating on quotations are called combinators; these are discussed in Using Combinators.

Implementation

A quotation is compiled as:

... code before quotation ... i liju....                    (if_compiling_only) d address after quotation     (if_compiling_only) ... code for quotation i re......                    (this_is_where_the_quote_ends) i li...... d address of code for quotation ... code after quotation ....

Quotations are used heavily in RETRO. They give the source a feel that's different from traditional Forth, and allow for a more consistent syntax.

For instance, in a traditional Forth, you might have some conditionals:

IF ... THEN IF ... ELSE ... THEN IF ... EXIT THEN

RETRO uses conditional combinators for these:

[ ... ] if [ ... ] [ ... ] choose [ ... ] if;

Or loops:

FOR ... NEXT

Is replaced by:

[ ... ] times

This can also extend to stack flow. Sequences like:

>R ... >R DUP >R ... >R

Become:

[ ... ] dip [ ... ] sip

And forms like:

1 2 3 * swap 3 * swap

Can be replaced with a combinator like:

#1 #2 [ #3 * ] bi@

While there is a different set of words to learn, I find that overall there's less noise from low level stack shuffling words and the added consistency with regards to overall syntax has been nice as I was never fond of the multiple forms that existed in traditional Forth.

Sockets

On Unix hosts, RETRO provides an optional set of words for using network sockets.

To create a new socket, just run:

socket:create

This will return a socket handle.

To bind to a port, pass the port number and socket handle to socket:bind. The port should be a string. This will return 0 if successful, -1 if not successful, and an error code.

'9998 @Sock socket:bind

To prepare a socket for incoming connections use socket:listen. This will take a backlog count and a socket handle. It returns a flag (0 success, -1 failed) and an error code.

#3 @Sock socket:listen

To accept connections pass the socket handle to socket:accept. This returns a new socket for the connection and an error code.

@Sock socket:accept

To connect to a server using the socket:

'forth.works '70 socket:configure @Sock socket:connect

socket:connect will return a status code and an error code.

To write a string to a socket, use socket:send. This will take a string and a socket handle and will return the number of bytes sent and an error code.

'test @Sock socket:send

To read data from a socket pass an address, a maximum number of bytes, and the socket handle to socket:recv. This will return the number of bytes received and an error code. The bytes will be stored in memory starting at the specified address.

here #1024 @Sock socket:recv

To close a socket, pass the socket handle to socket:close.

@Socket socket:close

RETRO on Unix hosts is designed to play well with scripting.

Shebang

To run an entire program directly, start the file with the standard shebang and make the file executable:

#!/usr/bin/env retro

This requires the retro binary to be in your path.

Arguments

RETRO provides several words in the script: namespace for accessing command line arguments.

The number of arguments can be accessed via script:arguments. This will return a number with the arguments, other than the script name.

script:arguments '%n_arguments_passed\n s:format s:put

To retreive an argument, pass the argument number to script:get-argument:

script:arguments [ I script:get-argument s:put nl ] indexed-times

And to get the name of the script, use script:name.

script:name s:put

Mixing

With use of the Unu literate format, it's possible to mix both shell and RETRO code into a single script. As an example, this is a bit of shell that runs itself via retro for each .retro file in the current directory tree:

#!/bin/sh

# shell part find . -name '*.retro' -print0 | xargs -0 -n 1 retro $0 exit

# retro part

This will scan a source file and do something with it:

~~~ ... do stuff ... ~~~

Strings in RETRO are NULL terminated sequences of values representing characters. Being NULL terminated, they can't contain a NULL (ASCII 0).

The character words in RETRO are built around ASCII, but strings can contain UTF8 encoded data if the host platform allows. Words like s:length will return the number of bytes, not the number of logical characters in this case.

Sigil

Strings begin with a single '.

'Hello 'This_is_a_string 'This_is_a_much_longer_string_12345_67890_!!!

RETRO will replace spaces with underscores. If you need both spaces and underscores in a string, escape the underscores and use s:format:

'This_has_spaces_and_under\_scored_words. s:format

Namespace

Words operating on strings are in the s: namespace.

Lifetime

At the interpreter, strings get allocated in a rotating buffer. This is used by the words operating on strings, so if you need to keep them around, use s:keep or s:copy to move them to more permanent storage.

In a definition, the string is compiled inline and so is in permanent memory.

You can manually manage the string lifetime by using s:keep to place it into permanent memory or s:temp to copy it to the rotating buffer.

Mutability

Strings are mutable. If you need to ensure that a string is not altered, make a copy before operating on it or see the individual glossary entries for notes on words that may do this automatically.

Searching

RETRO provides four words for searching within a string.

• s:contains/char?
• s:contains/string?
• s:index/char
• s:index/string

Comparisons

• s:eq?
• s:case

Extraction

To obtain a new string containing the first n characters from a source string, use s:left:

'Hello_World #5 s:left

To obtain a new string containing the last n characters from a source string, use s:right:

'Hello_World #5 s:right

If you need to extract data from the middle of the string, use s:substr. This takes a string, the offset of the first character, and the number of characters to extract.

'Hello_World #3 #5 s:substr

Joining

You can use s:append or s:prepend to merge two strings.

'First 'Second s:append 'Second 'First s:prepend

Tokenization

• s:tokenize
• s:tokenize-on-string
• s:split
• s:split-on-string

Conversions

To convert the case of a string, RETRO provides s:to-lower and s:to-upper.

s:to-number is provided to convert a string to an integer value. This has a few limitations:

• only supports decimal
• non-numeric characters will result in incorrect values

Cleanup

RETRO provides a handful of words for cleaning up strings.

s:chop will remove the last character from a string. This is done by replacing it with an ASCII:NULL.

s:trim removes leading and trailing whitespace from a string. For more control, there is also s:trim-left and s:trim-right which let you trim just the leading or trailing end as desired.

Combinators

• s:for-each
• s:filter
• s:map

Other

• s:evaluate
• s:copy
• s:reverse
• s:hash
• s:length
• s:replace
• s:format
• s:empty

As dicussed in the Lifetime subsection, temporary strings are allocated in a rotating buffer. The details of this can be altered by updating two variables.

| Variable      | Holds                                    | | ------------- | ---------------------------------------- | | TempStrings   | The number of temporary strings          | | TempStringMax | The maximum length of a temporary string |

For example, to increase the number of temporary strings to 48:

#48 !TempStrings

The defaults are:

| Variable      | Default | | ------------- | ------- | | TempStrings   | 32      | | TempStringMax | 512     |

It's also important to note that altering these will affect the memory map for all temporary buffers. Do not use anything already in the buffers after updating these or you will risk data corruption and possible crashes.

A combinator is a function that consumes functions as input. They are used heavily by the RETRO system.

Combinators are divided into three primary types: compositional, execution flow, and data flow.

Compositional

A compositional combinator takes elements from the stack and returns a new quote.

curry takes a value and a quote and returns a new quote applying the specified quote to the specified value. As an example,

```
:acc (n-)  here swap , [ dup v:inc fetch ] curry ;
```

This would create an accumulator function, which takes an initial value and returns a quote that will increase the accumulator by 1 each time it is invoked. It will also return the latest value. So:

```
#10 acc
dup call n:put
dup call n:put
dup call n:put
```

Combinators of this type execute other functions.

Fundamental

call takes a quote and executes it immediately.

```
[ #1 n:put ] call
&words call
```

Conditionals

RETRO provides three primary combinators for use with conditional execution of quotes. These are choose, if, and -if.

choose takes a flag and two quotes from the stack. If the flag is true, the first quote is executed. If false, the second quote is executed.

```
#-1 [ 'true s:put ] [ 'false s:put ] choose
 #0 [ 'true s:put ] [ 'false s:put ] choose
```

if takes a flag and one quote from the stack. If the flag is true, the quote is executed. If false, the quote is discarded.

```
#-1 [ 'true s:put ] if
 #0 [ 'true s:put ] if
```

-if takes a flag and one quote from the stack. If the flag is false, the quote is executed. If true, the quote is discarded.

```
#-1 [ 'false s:put ] -if
 #0 [ 'false s:put ] -if
```

RETRO also provides case and s:case for use when you have multiple values to check against. This is similar to a switch in C.

case takes two numbers and a quote. The initial value is compared to the second one. If they match, the quote is executed. If false, the quote is discarded and the initial value is left on the stack.

Additionally, if the first value was matched, case will exit the calling function, but if false, it returns to the calling function.

s:case works the same way, but for strings instead of simple values.

```
:test (n-)
  #1 [ 'Yes s:put ] case
  #2 [ 'No  s:put ] case
  drop 'No idea s:put ;
```

Looping

Several combinators are available for handling various looping constructs.

while takes a quote from the stack and executes it repeatedly as long as the quote returns a true flag on the stack. This flag must be well formed and equal -1 or 0.

```
#10 [ dup n:put sp n:dec dup 0 -eq? ] while
```

times takes a count and quote from the stack. The quote will be executed the number of times specified. No indexes are pushed to the stack.

```
#1 #10 [ dup n:put sp n:inc ] times drop
```

There is also a indexed-times variation that provides access to the loop index (via I) and parent loop indexes (via J and K).

```
#10 [ I n:put sp ] indexed-times
```

These combinators exist to simplify stack usage in various circumstances.

Preserving

Preserving combinators execute code while preserving portions of the data stack.

dip takes a value and a quote, moves the value off the main stack temporarily, executes the quote, and then restores the value.

```
#10 #20 [ n:inc ] dip
```

Would yield the following on the stack:

```
11 20
```

sip is similar to dip, but leaves a copy of the original value on the stack during execution of the quote. So:

```
#10 [ n:inc ] sip
```

Leaves us with:

```
11 10
```

Cleave

Cleave combinators apply multiple quotations to a single value or set of values.

bi takes a value and two quotes, it then applies each quote to a copy of the value.

```
#100 [ n:inc ] [ n:dec ] bi
```

tri takes a value and three quotes. It then applies each quote to a copy of the value.

```
#100 [ n:inc ] [ n:dec ] [ dup * ] tri
```

Spread

Spread combinators apply multiple quotations to multiple values. The asterisk suffixed to these function names signifies that they are spread combinators.

bi* takes two values and two quotes. It applies the first quote to the first value and the second quote to the second value.

```
#1 #2 [ n:inc ] [ #2 * ] bi*
```

tri* takes three values and three quotes, applying the first quote to the first value, the second quote to the second value, and the third quote to the third value.

```
#1 #2 #3 [ n:inc ] [ #2 * ] [ n:dec ] tri*
```

Apply

Apply combinators apply a single quotation to multiple values. The @ sign suffixed to these function names signifies that they are apply combinators.

bi@ takes two values and a quote. It then applies the quote to each value.

```
#1 #2 [ n:inc ] bi@
```

tri@ takes three values and a quote. It then applies the quote to each value.

```
#1 #2 #3 [ n:inc ] tri@
```

RETRO also provides for-each combinators for various data structures. The exact usage of these varies; consult the Glossary and relevant chapters for more details on these.

Word classes are one of the two elements at the heart of RETRO's interpreter.

There are different types of words in a Forth system. At a minimum there are data words, regular words, and immediate words. There are numerous approaches to dealing with this.

In RETRO I define special words which receive a pointer and decide how to deal with it. These are grouped into a class: namespace.

When a word is found in the dictionary, RETRO will push a pointer to the definition (the d:xt field) to the stack and then call the word specified by the d:class field.

The word called is responsible for processing the pointer passed to it.

As a simple case, let's look at immediate words. These are words which will always be called when encountered. A common strategy is to have an immediacy bit which the interpreter will look at, but RETRO uses a class for this. The class is defined:

```
:class:immediate (a-)  call ;
```

Or a normal word. These should be called at interpret time or compiled into definitions. The handler for this can look like:

```
:class:word (a-) compiling? [ compile:call ] [ call ] choose ;
```

The ability to add new classes is useful. If I wanted to add a category of word that preserves an input value, I could do it with a class:

```
:class:duplicating (a-)
  compiling? [ &dup compile:call ] [ &dup dip ] choose
  class:word ;  

:duplicating &class:duplicating reclass ;

:. n:put nl ; duplicating
#100 . . .
```

RETRO releases add and change things. You can use the Version variable to determine the version in use and react accordingly.

```
@Version #201906 eq? [ 'Needs_2019.6! s:put nl bye ] if
```

This can be also be used to conditionally load compatibility files:

```
(If_newer_than_2016.6,_load_aliases_for_renamed_words)
@Version #201906 gt? [ 'Renamed_2019.6.forth include ] if
```

The version is a six digit number encoding the year and month of the release. So:

201901  is  2019.1 201906  is  2019.6 201911  is  2019.11

A #100 /mod will suffice to split these if needed.

Errors

RETRO does only minimal error checking.

Non-Fatal

A non-fatal error will be reported on word not found during interactive or compile time. Note that this only applies to calls: if you try to get a pointer to an undefined word, the returned pointer will be zero.

Fatal

A number of conditions are known to cause fatal errors. The main ones are stack overflow, stack underflow, and division by zero.

On these, RETRO will generally exit. For stack depth issues, the VM will attempt to display an error prior to exiting.

In some cases, the VM may get stuck in an endless loop. If this occurs, try using CTRL+C to kill the process, or kill it using whatever means your host system provides.

Rationale

Error checks are useful, but slow - especially on a minimal system like RETRO. The overhead of doing depth or other checks adds up quickly.

As an example, adding a depth check to drop increases the time to use it 250,000 times in a loop from 0.16 seconds to 1.69 seconds.

RETRO has a single dictionary, but does provide a means of using lexical scope to keep this dictionary clean.

Example

```
{{
  'A var
  :++A  &A v:inc ;
---reveal---
  :B ++A ++A @A n:put nl ;
}}
```

In this example, the lexical namespace is created with {{. A variable (A) and word (++A) are defined. Then a marker is set with ---reveal---. Another word (B) is defined, and the lexical area is closed with }}.

The headers between {{ and ---reveal--- are then hidden from the dictionary, leaving only the headers between ---reveal--- and }} exposed.

If you wish to hide all headers in a {{ ... }} block, leave out the ---reveal---.

```
{{
  :a #3 ;
  :b a dup * ;
}}
```

Notes

This only affects word visibility within the scoped area. As an example:

```
:a #1 ;

{{
  :a #2 ;
---reveal---
  :b 'a s:evaluate n:put ;
}}
```

In this, after }} closes the area, the :a #2 ; is hidden and the s:evaluate will find the :a #1 ; when b is run.

Use of these words can result in a corrupt dictionary and system crashes. Specifically, use of ---reveal--- with an empty private or public section will result in dictionary corruption.

If you don't need private words, don't put them in a scope. And if you don't need public words, don't include the ---reveal---.

The stacks are a defining feature of Forth. They are are used to pass data between words and to track return addresses for function calls.

RETRO always has two stacks, and optionally (if built with floating point support) a third.

This is the primary stack. Values are placed here, passed to words which consume them and then return results. When I refer to "the stack", this is the one I mean. Learning to use the stack is a crucial part to making effective use of RETRO.

Values can be placed on the stack directly.

| Example        | Action                                   | | -------------- | ---------------------------------------- | | `#300123`      | Push the number `300123` to the stack    | | `$h`           | Push the ASCII code for `h` to the stack | | `'hello_world` | Push a pointer to a string to the stack  | | `&fetch`       | Push the address of `fetch` to the stack |

RETRO provides a number of shufflers for reordering items on the stack.

Some of the most common ones are:

| Word    | Before   | After    | | ------- |--------- | -------- | | dup     | #1       | #1 #1    | | drop    | #1 #2    | #1       | | swap    | #1 #2    | #2 #1    | | over    | #1 #2    | #1 #2 #1 | | tuck    | #1 #2    | #2 #1 #2 | | nip     | #1 #2    | #2       | | rot     | #1 #2 #3 | #3 #1 #2 |

You can use push and pop to move values to and from the address stack. Make sure you pop them back before the word ends or RETRO will crash. These two words can not be used at the interpreter.

There is also a special one, reorder, which allows for big stack restructuring. This is slow but can be very useful.

As an example, let's say we have four values:

#1 #2 #3 #4

And we want them to become:

#4 #3 #2 #1

Doing this with the basic shufflers is difficult. You could end up with something similar to:

swap rot push rot pop swap 

But with reorder, you can just express the before and after states:

'abcd 'dcba reorder

If you need to quickly empty the stack, use reset.

To find out how many items are on the stack, use depth.

You can display the stack by running dump-stack.

RETRO provides combinators for working with data order on the stack. These are covered in a later chapter and are worth learning to use as they can help provide a cleaner, more structured means of working.

Tips

The stack is not an array in addressable memory. Don't try to treat it like one.

This stack primarily holds return addresses for function calls. You normally won't need to directly interact with this stack, but you can use push and pop to move values between the data stack and this.

If you are using a build with floating point support a third stack will be present. Floating point values are kept and passed between words using this.

See the Floating Point chapter for more details on this.

Tips

I recommend keeping the data stack shallow. Don't try to juggle too much; it's better to factor definitions into shorter ones that deal with simpler parts of the stack values than to have a big definition with a lot of complex shuffling.

Notes

The standard system is configured with a very deep data stack (around 2,000 items) and an address stack that is 3x deeper. In actual use, your programs are unlikely to ever need this, but if you do, keep the limits in mind.

Nga has optional support for multiple virtual cores. These are not directly comparable to actual CPU cores, but do allow for a degree of multitasking.

Cores share a single address space for RAM, but each gets its own data and address stacks, as well as 24 internal registers for private data storage. The floating point stack is shared across all cores.

Execution is handled in a round-robin fashion. After an instruction bundle is processed, Nga will pass control to the next active core. Note that this means that execution will stall when an I/O operation is running.

Enabling

To make use of the multicore support, edit the Makefile and uncomment the lines reading:

# ENABLED += -DENABLE_MULTICORE # DEVICES += interface/multicore.retro

And rebuild.

Scheduling

Nga switches to the next active core after execution of an instruction bundle completes on the current core.

Initialization

To initialize a core, pass the core identifier (0 through 7) to core:init. This will zero out its internal registers and set it to.

Example:

#4 core:init

Initialization does not activate a core. To do this, you need to use core:start. Pass this the address of the word to run and the core number.

Example:

:a [ $a c:put ] forever ; &a #4 core:start

Two words are provided for suspending a core. The first is core:pause. Pass this the core number to pause.

Example:

#4 core:pause

The second option is intended if you need the currently active core to pause. This word is core:pause-current.

Example:

core:pause-current

To reactive a core, use core:resume. This takes the core number to activate.

Example:

#4 core:resume

Registers

Each core has 24 internal memory spaces. You can read these with core:rr and modify them with core:wr. (These are used identically to fetch and store). Registers are numbered as 0 through 23.

A core can not access the registers in another core.

Napia

The implementation here is based on the multicore model used in Napia, the virtual machine being written for the Retro on smaller targets. Code written to work with this will be usable on Retro/Napia with minimal changes.

The main differences are that under Nga, this is an optional extension, but in Napia, it is part of the standard system.

On startup, execution occurs on core 0, with only core 0 being initialized.

I/O is run on the currently active core. Since I/O is blocking, waiting for an interaction to occur will prevent other cores from running until the operation is complete.

Overview

At the heart of Retro is a simple MISC (minimal instruction set computer) processor for a dual stack architecture.

This is a very simple and straightforward system. There are 30 instructions. The memory is a linear array of signed 32 bit values. And there are two stacks: one for data and one for return addresses.

                                     |     Stacks      | | Opcode | Muri | Full Name          | Data  | Address | | ------ | ---- | ------------------ | ----- | ------- | |  0     | ..   | nop                |   -   |   -     | |  1     | li   | lit                |   -n  |   -     | |  2     | du   | dup                |  n-nn |   -     | |  3     | dr   | drop               |  n-   |   -     | |  4     | sw   | swap               | xy-yx |   -     | |  5     | pu   | push               |  n-   |   -n    | |  6     | po   | pop                |   -n  |  n-     | |  7     | ju   | jump               |  a-   |   -     | |  8     | ca   | call               |  a-   |   -A    | |  9     | cc   | conditional call   | af-   |   -A    | | 10     | re   | return             |   -   |  A-     | | 11     | eq   | equality           | xy-f  |   -     | | 12     | ne   | inequality         | xy-f  |   -     | | 13     | lt   | less than          | xy-f  |   -     | | 14     | gt   | greater than       | xy-f  |   -     | | 15     | fe   | fetch              |  a-n  |   -     | | 16     | st   | store              | na-   |   -     | | 17     | ad   | addition           | xy-n  |   -     | | 18     | su   | subtraction        | xy-n  |   -     | | 19     | mu   | multiplication     | xy-n  |   -     | | 20     | di   | divide & remainder | xy-rq |   -     | | 21     | an   | bitwise and        | xy-n  |   -     | | 22     | or   | bitwise or         | xy-n  |   -     | | 23     | xo   | bitwise xor        | xy-n  |   -     | | 24     | sh   | shift              | xy-n  |   -     | | 25     | zr   | zero return        |  n-?  |   -     | | 26     | ha   | halt               |   -   |   -     | | 27     | ie   | i/o enumerate      |   -n  |   -     | | 28     | iq   | i/o query          |  n-xy |   -     | | 29     | ii   | i/o invoke         | ...n- |   -     |

Encoding

Up to four instructions can be packed into each memory cell.

As an example,

Opcode 4 Opcode 3 Opcode 2 Opcode 1 00000000:00000000:00000000:00000000

If we have a bundle of duliswst, it would look like:

st       sw       li       du 00010000:00000100:00000001:00000010

Each li should have a value in the following cell(s). These values will be pushed to the stack. E.g., lili.... and 1, 2:

00000000:00000000:00000001:00000001 00000000 00000000 00000000 00000001 (1) 00000000 00000000 00000000 00000010 (2)

Shifts

sh performs a bitwise arithmetic shift operation.

This takes two values:

xy

And returns a single one:

z

If y is positive, this shifts x right by y bits. If negative, it shifts left.

The fe instruction allows queries of some data related to the Nga VM state. These are returned by reading from negative addresses:

| Address | Returns                | | ------- | ---------------------- | | -1      | Data stack depth       | | -2      | Address stack depth    | | -3      | Maximum Image Size     | | -4      | Minimum Integer Value  | | -5      | Maximum Integer Value  |

Nga provides three instructions for interacting with I/O devices. These are:

ie   i/o enumerate    returns the number of attached devices iq   i/o query        returns information about a device ii   i/o interact     invokes an interaction with a device

As an example, with an implementation providing an output source, a block storage system, and keyboard:

ie    will return `3` since there are three i/o devices 0 iq  will return 0 0, since the first device is a screen       (device class 0, version of 0) 1 iq  will return 1 3, since the second device is a block       storage (class 3), with a version of 1 2 iq  will return 0 1, since the third device is a keyboard       (class 1), with a version of 0

In this case, some interactions can be defined:

: c:put i liiire.. d 0

: c:get i liiire.. d 2

Setup the stack, push the device handle to the stack, and then use ii to invoke the interaction.

A Retro system requires one I/O device (a generic output for a single character). This must be the first device, and must have a device class of 0.

All other devices are optional and can be specified in any order.

The currently supported and reserved device identifiers are:

| ID   | Device Type      | Notes                      | | ---- | ---------------- | -------------------------- | | 0000 | Generic Output   | Always present as device 0 | | 0001 | Keyboard         |                            | | 0002 | Floating Point   |                            | | 0003 | Block Storage    | Raw, 1024 cell blocks      | | 0004 | Filesystem       | Unix-style Files           | | 0005 | Network: Gopher  | Make gopher requests       | | 0006 | Network: HTTP    | Make HTTP requests         | | 0007 | Network: Sockets |                            | | 0008 | Syscalls: Unix   |                            | | 0009 | Scripting Hooks  |                            | | 0010 | Random Number    |                            |

This list may be revised in the future. The only guaranteed stable indentifier is 0000 for generic output.

Nga provides a virtual processor and an extensible way of adding I/O devices, but does not provide any I/O itself. Adding I/O is the responsability of the interface layer.

An interface layer will wrap Nga, providing at least one I/O device (a generic output target), and a means of interacting with the retro image.

It's expected that this layer will be host specific, adding any system interactions that are needed via the I/O instructions. The image will typically be extended with words to use these.

Retro provides three words for interacting with I/O. These are:

io:enumerate    returns the number of attached devices io:query        returns information about a device io:invoke       invokes an interaction with a device

As an example, with an implementation providing an output source, a block storage system, and keyboard:

io:enumerate    will return `3` since there are three                 i/o devices #0 io:query     will return 0 0, since the first device                 is a screen (device class 0) with a version                 of 0 #1 io:query     will return 1 3, since the second device is                 block storage (device class 3), with a version                 of 1 #2 io:query     will return 0 1, since the last device is a                 keyboard (device class 1), with a version                 of 0

In this case, some interactions can be defined:

:c:put #0 io:invoke ; :c:get #2 io:invoke ;

Setup the stack, push the device handle, and then use io:invoke to invoke the interaction.

A Retro system requires one I/O device (a generic output for a single character). This must be the first device, and must have a device class and handle of 0.

All other devices are optional and can be specified in any order.

I/O devices on Nga are exposed via three instructions:

ie  enumerate i/o devices iq  query i/o device for class and version ii  invoke i/o interaction

All devices are registered with the VM. How this occurs is implementation dependent.

Use the ie instruction to return the number of attached devices.

i ie......

Upon running, the stack will contain the number of devices. You can then query these by passing the device number to iq.

Use iq to query an attached device. This will return two values, a device class and a revision number.

The device class will be the top value on the stack.

You can trigger an I/O operation by passing the device handle to the ii instruction.

E.g., to display a character (ASCII code 98 in this case):

i liliii.. d 98 d 0

Be sure to pass the device handle, not the device class.

Ultimately devices are implementation-specific, but the standard system provides or reserves the following:

 ID  | Device Class     | Notes                      | -----+------------------+----------------------------+ 0000 | Generic Output   | Always present as handle 0 | 0001 | Keyboard         |                            | 0002 | Floating Point   |                            | 0003 | Block Storage    | Raw, 1024 cell blocks      | 0004 | Filesystem       | Unix-style Files           | 0005 | Clock            |                            | 0006 |                  |                            | 0007 | Network: Sockets |                            | 0008 | Syscalls: Unix   |                            | 0009 | Scripting Hooks  |                            | 0010 | Random Number    |                            | 1000 | Image Saving     |                            |

It must be noted here that nothing forces devices to use these class identifiers, and one must take care to use an Nga implementation that provides the devices they need.

Over time, the functionality a device provides may change. To allow detection of this, the query functionality provides a revision number. Your code can use this to ensure that the device provided supports the level of functionality you need.

Supported by all Nga implementations. This is required to be the first device, and is the only one guaranteed to be provided. It consumes a value from the stack, writing to to the host-specific output. (This does not need to be a screen).

Read and return a keypress.

Consumes no data, returns a single value representing the character that was read.

No subcommands are defined.

The current revision is 1.

It currently provides:

n:to-float  (n-_f:-n) s:to-float  (s-_f:-n) f:to-number (f:a-__-n) f:to-string (f:n-__-s) f:+     (f:ab-c) f:-     (f:ab-c) f:*     (f:ab-c) f:/     (f:ab-c) f:floor (f:ab-c) f:ceiling (f:f-f) f:sqrt  (f:f-f) f:eq?   (f:ab-c) f:-eq?  (f:ab-c) f:lt?   (f:ab-c) f:gt?   (f:ab-c) f:depth (-n) f:dup   (f:a-aa) f:drop  (f:a-) f:swap  (f:ab-ba) f:log   (f:ab-c) f:power (f:ab-c) f:sin   (f:f-f) f:cos   (f:f-f) f:tan   (f:f-f) f:asin  (f:f-f) f:acos  (f:f-f) f:atan  (f:f-f) f:push  (f:f-) f:pop   (f:-f) f:adepth  (-n)

Reserved for future use.

Currently at revision 0.

This implements a device providing traditional Unix-like files.

Takes a value indicating an operation, and each operation takes additional values.

| Operation | Stack | Action                           | | --------- | ----- | -------------------------------- | | 0         | sm-h  | Open a file                      | | 1         | h-    | Close a file                     | | 2         | h-c   | Read a byte from a file          | | 3         | ch-   | Write a byte to a file           | | 4         | h-n   | Return current pointer into file | | 5         | nh-   | Move pointer in a file           | | 6         | h-n   | Return the size of a file        | | 7         | s-    | Delete a file                    | | 8         | h-    | Flush pending writes             |

This is currently at revision 0.

On invocation, this returns a random number.

On the C implementation, each I/O device has the needed support functions defined, then a query function and invocation function defined.

As an example, to add a device that has two functions, I might do:

void one() {   stack_push(100); }

void two() {   stack_push(200); }

Handler device_actions[] = {   one, two }

void io_device() {   device_actions[stack_pop()](); }

void query_device() {   stack_push(0);    /* Revision     */   stack_push(1234); /* Device Class */ }

Then add pointers to io_device to IO_deviceHandlers and query_device to IO_queryHandlers and increase the NUM_DEVICES by one.

You will then need to write a set of Retro words to use the new device.

:device:one #1 #1234 io:scan-for io:invoke ; :device:two #2 #1234 io:scan-for io:invoke ;

Rebuild the VM, adding these to image.

The actual Retro language is stored as a memory image for Nga.

Format

The image file is a flat, linear sequence of signed 32-bit values. Each value is stored in little endian format. The size is not fixed. An interface should check when loading to ensure that the physical image is not larger than the emulated memory.

Header

The image will start with two cells. The first is a liju.... instruction, the second is the target address for the jump. This serves to skip over the rest of the data and reach the actual entry point.

This is followed by a pointer to the most recent dictionary header, a pointer to the next free address in memory, and then the Retro version number.

| Offset | Contains                    | | ------ | --------------------------- | | 0      | lit call nop nop            | | 1      | Pointer to main entry point | | 2      | Dictionary                  | | 3      | Heap                        | | 4      | Retro version               |

The actual code starts after this header.

The version number is the year and month. As an example, the 12.2019.6 release will have a version number of 201906.

Layout

Assuming an Nga built with 524287 cells of memory:

| RANGE           | CONTAINS                     | | --------------- | ---------------------------- | | 0 - 1024        | Retro Core kernel            | | 1025 - 1535     | token input buffer           | | 1536 +          | start of heap space          | | ............... | free memory for your use     | | 506879          | buffer for string evaluate   | | 507904          | temporary strings (32 * 512) | | 524287          | end of memory                |

The buffers at the end of memory will resize when specific variables related to them are altered.

The C implementation of Retro provides several functions for interacting with code written in Retro.

Dictionary

The dictionary is a linked list, with a pointer to the most recent entry stored in address 2.

You can access the fields for each entry using:

d_link d_xt d_class d_name

Each takes a dictionary header address (the "dictionary token") and returns a pointer to the Retro address for the desired data.

To find a dictionary token, use d_lookup. This takes the address of the dictionary to search (memory[2] in most cases) and the name of the word to find.

There is also d_xt_for() which takes a name and a dictionary pointer and returns the execution token for the specified word.

Strings

Like C, Retro uses NUL terminated strings. But, since all addressing is 32-bit (or 64-bit, depending on your configuration), some conversion is needed.

To get a C version of a string, use string_extract(). This takes a Retro address and returns a pointer to a C string.

Example:

// Get the name of the most recently defined word string_extract(d_name(memory[2]));

To push a C string into Retro memory, use string_inject(). This takes a C string and a Retro address.

// Copy a string to the TIB buffer string_inject("hello", 1024);

Stack

You can push values to the stack with stack_push() and pop them off with stack_pop().

Interacting

If you have a word named hello that you wish to run:

execute(d_xt_for("hello", memory[2]));

If you want to evaluate a token as if it was typed into a Retro listener:

string_inject("token", 1024); stack_push(1024); execute("interpret", memory[2]);

The interpret word handles things like sigils, so this is needed if you want to run something that needs those.

Taken from http://lists.tunes.org/archives/tunes-lll/1999-July/000121.html

On Fri, Jul 30, 1999 at 07:43:54PM -0400, Paul Dufresne wrote:

> My brother did found it funny that Retro is called like that. > For him retro means going back (generally in time) so this > does not looks like a name of a OS to come. So he'd like to > know from where the name came.

Heheh, here's the story: When I started playing with OS stuff last year (not seriously), I was reading about some old things like FORTH and ITS, dating back to the 1960's and 70's. The past few years in America, there's been a revival of disco music (along with bell bottoms, platform shoes, and all that crap) and they call it "retro". Now, my OS was named by musicians.. I was telling a fellow musician about my ideas, how it would be cool to have a small OS that isn't bloated and unmanageable like Windows... go back to the 70's and resurrect a line of software that died out. He goes "hmm.. sounds kinda retro.."

I think it sounds kinda rebellious, which is a Good Thing now that everybody hates the M$ empire. :) It seems like other people are as sick of the future as I am. Look at TUNES, the idea there isn't to make some great new invention, just take some decades-old ideas and combine them in one OS. The first time I saw Knuth's "Art of Computer Programming" in the library I thought "god that looks old.. 1973!!! nevermind.." Now it's my programming bible. Find me something better published in the 90's.. if such a thing exists, it'll be like a needle in a haystack. "Newer" doesn't necessarily mean "better".

New cars = flimsier New farming methods = more devastating New version of Netscape = more bloat, more bullshit

One thing is better now: computer hardware. Give me 70's software on 90's and 00's hardware :)

• Tom Novelli <tcn@tunes.org>

Computer software is a technology in its infancy, a mere fifty years old. The last 25 years in particular have seen an explosion in the software business. However, software has seen little innovation while hardware technology has improved phenomenally (notwithstanding the advent of lousy slave-made parts). Proven software techniques of forty years ago have yet to reach widespread use, in deference to the "latest and greatest" proprietary solutions of dubious value. Thanks to agressive marketing, we make huge investments in these dead-end technologies (through our businesses and governments, if not personally) and we end up with a reliance on a heap of complicated, error-prone, poorly understood junk software.

Complexity will dominate the software industry for the foreseeable future. The Retro philosophy is a simple alternative for those willing to make a clean break with legacy software. A Retro system can communicate with other systems, but it won't run much legacy software, especially proprietary software without source code. An emulation layer could be added, but doing so would defeat the purpose of a simple operating system. I think TCP/IP support is all the compatibility that's needed.

At first Retro will appeal to computer hobbyists and electronic engineers. Once the rough edges are smoothed out, it could catch on with ordinary folks who don't like waiting five minutes just to check their email (not to mention the long hours of setup and maintenance). Game programmers who take their craft seriously may also be interested. Businesses might even see a use for it, if the managers decide it's more cost-effective to carefully design software for specific needs, rather than buying off-the-shelf crap and spending countless manhours working around the bugs. Since it's not practical for businesses to make a clean break, my advice is to run Retro (and its ilk) on separate machines connected by a network. Retro is efficient enough to run on older machines that would otherwise sit idle, being too slow for the latest Microsoft bloatware (or Linux, for that matter).

I strive to avoid the extraneous. That applies even to proven technologies, if I don't need them. If my computer isn't set up for people to log in over the network, I don't want security features; they just get in the way. If I'm only running programs I wrote, I should be able to run them with full access to the hardware; I don't need protection from viruses. If I download something I don't trust, then I can run it in an isolated process, which is customary with Unix and kin. But that's not core functionality. All that's needed is the flexibility to add things like security, graphical interfaces, and distributed processing - if the need ever arises.

In programming languagues, I was misled. It's the Tower of Babel all over again. The thousands of languages in existence all fall into a handful of archetypes: Assembler, LISP, FORTRAN and FORTH represent the earliest descendants of nearly all languages. I hesitate to name a definitive "object-oriented" language, and here's why: Object-Oriented programming is just a technique, and any language will suffice, even Assembler. The complexites of fancy languages like Ada and C++ are a departure from reality -- the reality of the actual physical machine. When it all boils down, even LISP, FORTRAN and FORTH are only extensions of the machine.

I chose FORTH as the "native tongue" of Retro. LISP, FORTRAN, and other languages can be efficiently implemented as extensions of FORTH, but the reverse isn't so efficient. Theoretically all languages are equivalent, but when design time, compilation time, and complexity are accounted for, FORTH is most efficient. FORTH also translates most directly to the hardware. (In fact, FORTH has been implemented in hardware; these "stack machines" are extremely efficient.) FORTH is also the easiest language to implement from scratch - a major concern when you're trying to make a clean break. So with simplicity in mind, FORTH was the obvious choice.

I'm perfectly happy working with text only, and I go to great lengths to avoid using the standard graphical environments, which have major problems: windows, pulldown menus, and mice. Windows can't share the screen nicely; that idea is hopeless. Pulldowns are tedious. Mice get in the way of typing without reducing the need for it; all they give me is tendonitis. Their main use is for drawing.

Some of my favorite interfaces: Telix, Telegard BBS, Pine, Pico, Lynx, and ScreamTracker. All "hotkey" interfaces where you press a key or two to perform an action. Usually the important commands are listed at the bottom of the screen, or at least on a help screen. The same principles apply to graphical interfaces: use the full screen, except for a status and menu area on one edge. Resist the temptation to clutter up the screen.

As for switching between programs, the Windows methods suck; the only thing worse is Unix job control (jobs, fg, and such). The Linux method is tolerable: Alt-Arrows, Alt-F1, Alt-F2, etc. Still, things could be better: F11 and F12 cycle back and forth through all open programs; Alt-F1 assigns the currently selected program to F1, and likewise for the other function keys. Programs just won't use function keys - Control and Alt combinations are less awkward and easier to remember, besides. I'll also want a "last channel" key and a "task list" key; maybe I'll borrow those stupid Win95 keys. The Pause key will do like it says - pause the current program - and Ctrl-Pause (Break) will kill it.

One more thing: consistency. I like programs to look different so I can tell them apart, but the keys should be the same as much as possible. Keys should be configured in one place, for all programs. Finally, remember the most consistent interface, one of the few constants throughout the history of computing - the text screen and keyboard, and the teletypewriter before that. Don't overlook it.

More to come, maybe... :)

"If it's on line, it's a work in progress."

Tom Novelli, 3/4/2000

Retro 10 and 11 were written in themselves using a metacompiler. I had been fascinated by this idea for a long time and was able to explore it heavily. While I still find it to be a good idea, the way I ended up doing it was problematic.

The biggest issue I faced was that I wanted to do this in one step, where loading the Retro source would create a new image in place of the old one, switch to the new one, and then load the higher level parts of the language over this. In retrospect, this was a really bad idea.

My earlier design for Retro was very flexible. I allowed almost everything to be swapped out or extended at any time. This made it extremely easy to customize the language and environment, but made it crucial to keep track of what was in memory and what had been patched so that the metacompiler wouldn't refer to anything in the old image during the relocation and control change. It was far too easy to make a mistake, discover that elements of the new image were broken, and then have to go and revert many changes to try to figure out what went wrong.

This was also complicated by the fact that I built new images as I worked, and, while a new image could be built from the last built one, it wasn't always possible to build a new image from the prior release version. (Actually, it was often worse - I failed to check in every change as I went, so often even the prior commits couldn't rebuild the latest images).

For Retro 12 I wanted to avoid this problem, so I decided to go back to writing the kernel ("Rx") in assembly. I actually wrote a Machine Forth dialect to generate the initial assembly, before eventually hand tuning the final results to its current state.

I could (and likely will eventually) write the assembler in Retro, but the current one is in C, and is built as part of the standard toolchain.

My VM actually has two assemblers. The older one is Naje. This was intended to be fairly friendly to work with, and handles many of the details of packing instructions for the user. Here is an example of a small program in it:

:square   dup   mul   ret :main   lit 35   lit &square   call   end

The other assembler is Muri. This is a far more minimalistic assembler, but I've actually grown to prefer it. The above example in Muri would become:

i liju.... r main : square i dumure.. : main i lilica.. d 35 r square i en......

In Muri, each instruction is reduced to two characters, and the bundlings are listed as part of an instruction bundle (lines starting with i). This is less readable if you aren't very familiar with Nga's assembly and packing rules, but allows a very quick, efficient way of writing assembly for those who are.

I eventually rewrote the kernel in the Muri style as it's what I prefer, and since there's not much need to make changes in it.

Retro is an image based Forth system running on a lightweight virtual machine. This is the story of how that image is made.

The first Retro to use an image based approach was Retro 10. The earliest images were built using a compiler written in Toka, an earlier experimental stack language I had written. It didn't take long to want to drop the dependency on Toka, so I rewrote the image compiler in Retro and then began development at a faster pace.

Retro 11 was built using the last Retro 10 image and an evolved version of the metacompiler. This worked well, but I eventually found it to be problematic.

One of the issues I faced was the inability to make a new image from the prior stable release. Since I develop and test changes incrementally, I reached a point where the current metacompiler and image required each other. This wasn't a fatal flaw, but it was annoying.

Perhaps more critical was the fragility of the system. In R11 small mistakes could result in a corrupt image. The test suite helped identify some of these, but there were a few times I was forced to dig back through the version control history to recover a working image.

The fragile nature was amplified by some design decisions. In R11, after the initial kernel was built, it would be moved to memory address 0, then control would jump into the new kernel to finish building the higher level parts.

Handling this was a tricky task. In R11 almost everything could be revectored, so the metacompiler had to ensure that it didn't rely on anything in the old image during the move. This caused a large number of issues over R11's life.

So on to Retro 12. I decided that this would be different. First, the kernel would be assembly, with an external tool to generate the core image. The kernel is in image/retro.muri and the assembler is Muri. To load the standard library, I wrote a second tool, Retro-extend. This separation has allowed me many fewer headaches as I can make changes more easily and rebuild from scratch when necessary.

But I miss self-hosting. So last fall I decided to resolve this. And today I'm pleased to say that it is now done.

There are a few parts to this.

Unu. I use a Markdown variation with fenced code blocks. The tool I wrote in C to extract these is called unu. For a self hosting Retro, I rewrote this as a combinator that reads in a file and runs another word against each line in the file. So I could display the code block contents by doing:

'filename [ s:put nl ] unu

This made it easier to implement the other tools.

Muri. This is my assembler. It's minimalistic, fast, and works really well for my purposes. Retro includes a runtime version of this (using as{, }as, i, d, and r), so all I needed for this was to write a few words to parse the lines and run the corresponding runtime words. As with the C version, this is a two pass assembler.

Muri generates a new ngaImage with the kernel. To create a full image I needed a way to load in the standard library and I/O extensions.

This is handled by retro-extend. This is where it gets more complex. I implemented the Nga virtual machine in Retro to allow this to run the new image in isolation from the host image. The new ngaImage is loaded, the interpreter is located, and each token is passed to the interpreter. Once done, the new image is written to disk.

So at this point I'm pleased to say that I can now develop Retro using only an existing copy of Retro (VM+image) and tools (unu, muri, retro-extend, and a line oriented text editor) written in Retro.

This project has delivered some additional side benefits. During the testing I was able to use it to identify a few bugs in the I/O extensions, and the Nga-in-Retro will replace the older attempt at this in the debugger, allowing a safer testing environment.

What issues remain?

The extend process is slow. On my main development server (Linode 1024, OpenBSD 6.4, 64-bit) it takes a bit over five minutes to complete loading the standard library, and a few additional depending on the I/O drivers selected.

Most of the performance issues come from running Nga-in-Retro to isolate the new image from the host one. It'd be possible to do something a bit more clever (e.g., running a Retro instance using the new image via a subprocess and piping in the source, or doing relocations of the data), but this is less error prone and will work on all systems that I plan to support (including, with a few minor adjustments, the native hardware versions [assuming the existance of mass storage]).

Sources:

Unu

• http://forth.works/c8820f85e0c52d32c7f9f64c28f435c0
• gopher://forth.works/0/c8820f85e0c52d32c7f9f64c28f435c0

Muri

• http://forth.works/09d6c4f3f8ab484a31107dca780058e3
• gopher://forth.works/0/09d6c4f3f8ab484a31107dca780058e3

retro-extend

• http://forth.works/c812416f397af11db58e97388a3238f2
• gopher://forth.works/0/c812416f397af11db58e97388a3238f2

A big change in Retro 12 was the elimination of the traditional parser from the language. This was a sacrifice due to the lack of an I/O model. Retro has no way to know how input is given to the interpret word, or whether anything else will ever be passed into it.

And so interpret operates only on the current token. The core language does not track what came before or attempt to guess at what might come in the future.

This leads into the sigils. Retro 11 had a complicated system for sigils, with different types of sigilss for words that parsed ahead (e.g., strings) and words that operated on the current token (e.g., @). Retro 12 eliminates all of these in favor of just having a single sigil model.

The first thing interpret does is look to see if the first character in a token matches a sigil: word. If it does, it passes the rest of the token as a string pointer to the sigil specific handler to deal with. If there is no valid sigil found, it tries to find it in the dictionary. Assuming that it finds the words, it passes the d:xt field to the handler that d:class points to. Otherwise it calls err:notfound.

This has an important implication: words can not reliably have names that start with a sigil character.

It also simplifies things. Anything that would normally parse becomes a sigil handler. So creating a new word? Use the : sigil. Strings? Use '. Pointers? Try &. And so on. E.g.,

In ANS                  | In Retro : foo ... ;             | :foo ... ; ' foo                   | &foo : bar ... ['] foo ;     | :bar ... &foo ; s" hello world!"        | 'hello_world!

If you are familiar with ColorForth, sigils are a similar idea to colors, but can be defined by the user as normal words.

After doing this for quite a while I rather like it. I can see why Chuck Moore eventually went towards ColorForth as using color (or sigils in my case) does simplify the implementation in many ways.

In implementing the Retro 12 kernel (called Retro Core, and defined in image/retro.muri) I had to decide on what functionality would be needed. It was important to me that this be kept clean and minimalistic, as I didn't want to spend a lot of time changing it as time progressed. It's far nicer to code at the higher level, where the Retro language is fully functional, as opposed to writing more assembly code.

So what made it in?

Primitives

These are words that map directly to Nga instructions.

dup      drop     swap   call   eq?   -eq?   lt?   gt? fetch    store    +      -      *     /mod   and   or xor      shift    push   pop    0;

Memory

fetch-next    store-next    ,    s,

Strings

s:to-number    s:eq?    s:length

Flow Control

choose    if    -if    repeat    again

Compiler & Interpreter

Compiler    Heap        ;       [    ]      Dictionary d:link      d:class     d:xt    d:name      d:add-header class:word  class:primitive     class:data  class:macro sigil::     sigil:#     sigil:& sigil:$ interpret   d:lookup    err:notfound

Assembler

i           d           r

I could slightly reduce this. The $ sigil could be defined in higher level code, and I don't strictly need to expose the fetch-next and store-next here. But since the are already implemented as dependencies of the words in the kernel, it would be a bit wasteful to redefine them later in higher level code.

A recent change was the addition of the assembler into the kernel. This allows the higher levels to use assembly as needed, which gives more flexibility and allows for more optimal code in the standard library.

With these words the rest of the language can be built up. Note that the Retro kernel does not provide any I/O words. It's assumed that the Retro interfaces will add these as best suited for the systems they run on.

There is another small bit. All images start with a few key pointers in fixed offsets of memory. These are:

| Offset | Contains                    | | ------ | --------------------------- | | 0      | lit call nop nop            | | 1      | Pointer to main entry point | | 2      | Dictionary                  | | 3      | Heap                        | | 4      | Retro version identifier    |

An interface can use the dictionary pointer and knowledge of the dictionary format for a specific Retro version to identify the location of essential words like interpret and err:notfound when implementing the user facing interface.

When I decided to begin work on what became Retro 12, I knew the process would involve updating Ngaro, the virtual machine that Retro 10 and 11 ran on.

Ngaro rose out of an earlier experimental virtual machine I had written back in 2005-2006. This earlier VM, called Maunga, was very close to what Ngaro ended up being, though it had a very different approach to I/O. (All I/O in Maunga was intended to be memory mapped; Ngaro adopted a port based I/O system).

Ngaro itself evolved along with Retro, gaining features like automated skipping of NOPs and a LOOP opcode to help improve performance. But the I/O model proved to be a problem. When I created Ngaro, I had the idea that I would always be able to assume a console/terminal style environment. The assumption was that all code would be entered via the keyboard (or maybe a block editor), and that proved to be the fundamental flaw as time went on.

As Retro grew it was evident that the model had some serious problems. Need to load code from a file? The VM and language had functionality to pretend it was being typed in. Want to run on something like a browser, Android, or iOS? The VM would need to be implemented in a way that simulates input being typed into the VM via a simulated keyboard. And Retro was built around this. I couldn't change it because of a promise to maintain, as much as possible, source compatibility for a period of at least five years.

When the time came to fix this, I decided at the start to keep the I/O model separate from the core VM. I also decided that the core Retro language would provide some means of interpreting code without requiring an assumption that a traditional terminal was being used.

So Nga began. I took the opportunity to simplify the instruction set to just 26 essential instructions, add support for packing multiple instructions per memory location (allowing a long due reduction in memory footprint), and to generally just make a far simpler design.

I've been pleased with Nga. On its own it really isn't useful though. So with Retro I embed it into a larger framework that adds some basic I/O functionality. The interfaces handle the details of passing tokens into the language and capturing any output. They are free to do this in whatever model makes most sense on a given platform.

So far I've implemented:

- a scripting interface, reading input from a file and   offering file i/o, gopher, and reading from stdin, and   sending output to stdout. - an interactive interface, built around ncurses, reading   input from stdin, and displaying output to a scrolling   buffer. - an iOS interface, built around a text editor, directing   output to a separate interface pane. - an interactive block editor, using a gopher-based block   data store. Output is displayed to stdout, and input is   done via the blocks being evaluated or by reading from   stdin.

In all cases, the only common I/O word that has to map to an exposed instruction is putc, to display a single character to some output device. There is no requirement for a traditional keyboard input model.

By doing this I was able to solve the biggest portability issue with the Retro 10/11 model, and make a much simpler, cleaner language in the end.

So it's now been about five years since the last release of Retro 11. While I still see some people obtaining and using it, I've moved on to the twelth generation of Retro. It's time for me to finally retire Retro 11.

As I prepare to do so, I thought I'd take a brief look back.

Retro 11 began life in 2011. It grew out of Retro 10, which was the first version of Retro to not be written in x86 assembly language. For R10 and R11, I wrote a portable virtual machine (with numerous implementations) and the Forth dialect was kept in an image file which ran on the VM.

Retro 10 worked, but was always a bit too sloppy and changed drastically between releases. The major goal of Retro 11 was to provide a stable base for a five year period. In retrospect, this was mostly achieved. Code from earlier releases normally needed only minor adjustments to run on later releases, though newer releases added significantly to the language.

There were seven releases.

• Release 11.0: 2011, July
• Release 11.1: 2011, November
• Release 11.2: 2012, January
• Release 11.3: 2012, March
• Release 11.4: 2012, July
• Release 11.5: 2013, March
• Release 11.6: 2014, August

Development was fast until 11.4. This was the point at which I had to slow down due to RSI problems. It was also the point which I started experiencing some problems with the metacompiler (as discussed previously).

Retro 11 was flexible. All colon definitions were setup as hooks, allowing new functionality to be layered in easily. This allowed the later releases to add things like vocabularies, search order, tab completion, and keyboard remapping. This all came at a cost though: later things could use the hooks to alter behavior of existing words, so it was necessary to use a lot of caution to ensure that the layers didn't break the earlier code.

The biggest issue was the I/O model. Retro 11 and the Ngaro VM assumed the existence of a console environment. All input was required to be input at the keyboard, and all output was to be shown on screen. This caused some problems. Including code from a file required some tricks, temporarily rewriting the keyboard input function to read from the file. It also became a major issue when I wrote the iOS version. The need to simulate the keyboard and console complicated everything and I had to spend a considerable amount of effort to deal with battery performance resulting from the I/O polling and wait states.

But on the whole it worked well. I used Retro 11.6 until I started work on Retro 12 in late 2016, and continued running some tools written in R11 until the first quarter of last year.

The final image file was 23,137 cells (92,548 bytes). This was bloated by keeping some documentation (stack comments and short descriptions) in the image, which started in 11.4. This contained 269 words.

I used Retro 11 for a wide variety of tasks. A small selection of things that were written includes:

• a pastebin
• front end to ii (irc client)
• small explorations of interactive fiction
• irc log viewer
• tool to create html from templates
• tool to automate creation of an SVCD from a set of photos
• tools to generate reports from data sets for my employer

In the end, I'm happy with how Retro 11 turned out. I made some mistakes in embracing too much complexity, but despite this it was a successful system for many years.

The standard Retro is not a good choice for applications needing to be highly secure.

The Retro system performs only minimal checks. It will not load an image larger than the max set at build time. And stack over/underflow are checked for as code executes.

The system does not attempt to validate anything else, it's quite easy to crash.

Isolation

The VM itself and the core code is self contained. Nga does not make use of malloc/free, and uses only standard system libraries. It's possible for buffer overruns within the image (overwriting Nga code), but the Retro image shouldn't leak into the C portions.

I/O presents a bigger issue. Anything involving I/O, especially with the unix: words, may be a vector for attacks.

I'm not planning to add anything to the image side as, for me, the performance hit due to added checks is bigger than the benefits.

The story is different on the VM side. I've already begun taking steps to address some of the issues, using functions that check for overruns with strings and doing some minor testing for these conditions. I will be gradually addressing the various I/O related extensions, though it's unlikely to ever be fully guarded against attacks.

Rationale

Retro is, primarily, a personal system. I'm running code I wrote to solve problems I face. On the occasions where I run code sent to me by others, I read it carefully first and then run inside a sandboxed environment if I'm worried about anything in it.

In brief: don't use underscores in word names.

There is a good reason for this, and it has to do with how Retro processes strings. By default, underscores in strings are replaced by spaces. This is problematic when dealing with words like var, const, and d:create which take word names as strings.

Consider:

:hello_msg 'hello_user ; 'test_name var #188 !test_name

In the first case, the : sigil handles the token, so the underscore is not remapped to a space, creating a word name as hello_msg. But in the second, the ' sigil remaps the underscore to a space, giving a variable name of test name. In the third line, the name lookup will fail as test_name is not defined, so the store will be done to an incorrect address.

Because of this, it's best to avoid underscores in names.

Having covered this, if you do need to use them for some reason, you can replace d:add-header with a version that remaps spaces back to underscores before creating the header. The following will allow for this.

~~~ {{   :fields        @Dictionary , (link) , (xt) , (class) ;   :invalid-name? dup ASCII:SPACE s:contains/char? ;   :rewrite       [ ASCII:SPACE [ $_ ] case ] s:map ;   :entry         here &call dip !Dictionary ;   [ [ fields invalid-name? &rewrite if s, (name) ] entry ] }}

#1793 &d:add-header store &d:add-header n:inc store ~~~

Additional Note:

Some version of Retro have included the above patch. The last release that will include this by default is 2020.4 as it is not needed by the majority of users. If you want to keep it in your system, you will need to load it yourself or add it to your package/list.forth (for Unix users) before building.

We use software for our everyday needs because we want to get something done. We have goals to achieve and things to do.

The software we use is coded by brave programmers that have their own goals. Most of the time there is an overlap between their goals and ours.

Over time these will diverge.

This means that the tools we depend on grow features we don't use or understand. There will be bugs in these code parts which will prevent us from reaching our goals.

So we are at a fork in the road:

• We have the choice of trying to understand the code and
fix it. • We have the choice of trying another program, whose
creator's goals are closer to ours. • We also have the choice of coding the software ourself.

All but the last path mean endless seeking, evaluating and further deviation from our goals. Therefore we replace programs we do not understand fully with our own implementation.

The followers of the Code It Yourself Manifesto believe in these things:

• We implement it according to our own goals.
• We make mistakes and learn from them.
• We learn how our tools we depend on need to work.
• We gain a deep understanding of our problem domain.
• We still embrace sharing of ideas and code.

Sharing is only possible if we are excellent developers to each other. The next developer reading our code will be us in a not so distant future. Coding It Ourselves means we will document our code, clearly stating the goal of the software we write.

Together we enjoy the diversity of implementations and ideas.

We encourage our colleagues to

Code It Yourself.

Written by Christian Kellermann on 2016-01-12, licensed under a CreativeCommonsAttribution-ShareAlike3.0UnportedLicense.

Original text taken from http://pestilenz.org/~ckeen/blog/posts/ciy-manifesto.html

As Retro evolves, some words will become obsolete and no longer be needed. In each release, these will be marked as deprecated in the glossary. Any deprecated words will be removed in the next quarterly release.

E.g., if 2020.1 had deprecated words, these would be removed in the 2020.4 release. Any words made deprecated in between 2020.1 and 2020.4 would be removed in the 2020.7 release.

The text in these files is Copyright (c) 2018-2020 by Charles Childers.

To the extent possible under law, Charles Childers has waived all copyright and related or neighboring rights to the Retro Documentation. This work is published from: United States.

The historical papers are Copyright (c) 1999-2000 by Tom Novelli.

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• to Distribute and Publicly Perform the Work including as incorporated in
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• to Distribute and Publicly Perform Adaptations.

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You may Distribute or Publicly Perform the Work only under the terms of this License. You must include a copy of, or the Uniform Resource Identifier (URI) for, this License with every copy of the Work You Distribute or Publicly Perform. You may not offer or impose any terms on the Work that restrict the terms of this License or the ability of the recipient of the Work to exercise the rights granted to that recipient under the terms of the License. You may not sublicense the Work. You must keep intact all notices that refer to this License and to the disclaimer of warranties with every copy of the Work You Distribute or Publicly Perform. When You Distribute or Publicly Perform the Work, You may not impose any effective technological measures on the Work that restrict the ability of a recipient of the Work from You to exercise the rights granted to that recipient under the terms of the License. This Section 4(a) applies to the Work as incorporated in a Collection, but this does not require the Collection apart from the Work itself to be made subject to the terms of this License. If You create a Collection, upon notice from any Licensor You must, to the extent practicable, remove from the Collection any credit as required by Section 4(c), as requested. If You create an Adaptation, upon notice from any Licensor You must, to the extent practicable, remove from the Adaptation any credit as required by Section 4(c), as requested.

You may Distribute or Publicly Perform an Adaptation only under the terms of: (i) this License; (ii) a later version of this License with the same License Elements as this License; (iii) a Creative Commons jurisdiction license (either this or a later license version) that contains the same License Elements as this License (e.g., Attribution-ShareAlike 3.0 US)); (iv) a Creative Commons Compatible License. If you license the Adaptation under one of the licenses mentioned in (iv), you must comply with the terms of that license. If you license the Adaptation under the terms of any of the licenses mentioned in (i), (ii) or (iii) (the "Applicable License"), you must comply with the terms of the Applicable License generally and the following provisions: (I) You must include a copy of, or the URI for, the Applicable License with every copy of each Adaptation You Distribute or Publicly Perform; (II) You may not offer or impose any terms on the Adaptation that restrict the terms of the Applicable License or the ability of the recipient of the Adaptation to exercise the rights granted to that recipient under the terms of the Applicable License; (III) You must keep intact all notices that refer to the Applicable License and to the disclaimer of warranties with every copy of the Work as included in the Adaptation You Distribute or Publicly Perform; (IV) when You Distribute or Publicly Perform the Adaptation, You may not impose any effective technological measures on the Adaptation that restrict the ability of a recipient of the Adaptation from You to exercise the rights granted to that recipient under the terms of the Applicable License. This Section 4(b) applies to the Adaptation as incorporated in a Collection, but this does not require the Collection apart from the Adaptation itself to be made subject to the terms of the Applicable License.

If You Distribute, or Publicly Perform the Work or any Adaptations or Collections, You must, unless a request has been made pursuant to Section 4(a), keep intact all copyright notices for the Work and provide, reasonable to the medium or means You are utilizing: (i) the name of the Original Author (or pseudonym, if applicable) if supplied, and/or if the Original Author and/or Licensor designate another party or parties (e.g., a sponsor institute, publishing entity, journal) for attribution ("Attribution Parties") in Licensor's copyright notice, terms of service or by other reasonable means, the name of such party or parties; (ii) the title of the Work if supplied; (iii) to the extent reasonably practicable, the URI, if any, that Licensor specifies to be associated with the Work, unless such URI does not refer to the copyright notice or licensing information for the Work; and (iv) , consistent with Ssection 3(b), in the case of an Adaptation, a credit identifying the use of the Work in the Adaptation (e.g., "French translation of the Work by Original Author," or "Screenplay based on original Work by Original Author"). The credit required by this Section 4(c) may be implemented in any reasonable manner; provided, however, that in the case of a Adaptation or Collection, at a minimum such credit will appear, if a credit for all contributing authors of the Adaptation or Collection appears, then as part of these credits and in a manner at least as prominent as the credits for the other contributing authors. For the avoidance of doubt, You may only use the credit required by this Section for the purpose of attribution in the manner set out above and, by exercising Your rights under this License, You may not implicitly or explicitly assert or imply any connection with, sponsorship or endorsement by the Original Author, Licensor and/or Attribution Parties, as appropriate, of You or Your use of the Work, without the separate, express prior written permission of the Original Author, Licensor and/or Attribution Parties.

Except as otherwise agreed in writing by the Licensor or as may be otherwise permitted by applicable law, if You Reproduce, Distribute or Publicly Perform the Work either by itself or as part of any Adaptations or Collections, You must not distort, mutilate, modify or take other derogatory action in relation to the Work which would be prejudicial to the Original Author's honor or reputation. Licensor agrees that in those jurisdictions (e.g. Japan), in which any exercise of the right granted in Section 3(b) of this License (the right to make Adaptations) would be deemed to be a distortion, mutilation, modification or other derogatory action prejudicial to the Original Author's honor and reputation, the Licensor will waive or not assert, as appropriate, this Section, to the fullest extent permitted by the applicable national law, to enable You to reasonably exercise Your right under Section 3(b) of this License (right to make Adaptations) but not otherwise.

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UNLESS OTHERWISE MUTUALLY AGREED TO BY THE PARTIES IN WRITING, LICENSOR OFFERS THE WORK AS-IS AND MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND CONCERNING THE WORK, EXPRESS, IMPLIED, STATUTORY OR OTHERWISE, INCLUDING, WITHOUT LIMITATION, WARRANTIES OF TITLE, MERCHANTIBILITY, FITNESS FOR A PARTICULAR PURPOSE, NONINFRINGEMENT, OR THE ABSENCE OF LATENT OR OTHER DEFECTS, ACCURACY, OR THE PRESENCE OF ABSENCE OF ERRORS, WHETHER OR NOT DISCOVERABLE. SOME JURISDICTIONS DO NOT ALLOW THE EXCLUSION OF IMPLIED WARRANTIES, SO SUCH EXCLUSION MAY NOT APPLY TO YOU.

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7. Termination

This License and the rights granted hereunder will terminate automatically upon any breach by You of the terms of this License. Individuals or entities who have received Adaptations or Collections from You under this License, however, will not have their licenses terminated provided such individuals or entities remain in full compliance with those licenses. Sections 1, 2, 5, 6, 7, and 8 will survive any termination of this License. Subject to the above terms and conditions, the license granted here is perpetual (for the duration of the applicable copyright in the Work). Notwithstanding the above, Licensor reserves the right to release the Work under different license terms or to stop distributing the Work at any time; provided, however that any such election will not serve to withdraw this License (or any other license that has been, or is required to be, granted under the terms of this License), and this License will continue in full force and effect unless terminated as stated above. 8. Miscellaneous

Each time You Distribute or Publicly Perform the Work or a Collection, the Licensor offers to the recipient a license to the Work on the same terms and conditions as the license granted to You under this License.

Each time You Distribute or Publicly Perform an Adaptation, Licensor offers to the recipient a license to the original Work on the same terms and conditions as the license granted to You under this License.

If any provision of this License is invalid or unenforceable under applicable law, it shall not affect the validity or enforceability of the remainder of the terms of this License, and without further action by the parties to this agreement, such provision shall be reformed to the minimum extent necessary to make such provision valid and enforceable.

No term or provision of this License shall be deemed waived and no breach consented to unless such waiver or consent shall be in writing and signed by the party to be charged with such waiver or consent.

This License constitutes the entire agreement between the parties with respect to the Work licensed here. There are no understandings, agreements or representations with respect to the Work not specified here. Licensor shall not be bound by any additional provisions that may appear in any communication from You. This License may not be modified without the mutual written agreement of the Licensor and You.

The rights granted under, and the subject matter referenced, in this License were drafted utilizing the terminology of the Berne Convention for the Protection of Literary and Artistic Works (as amended on September 28, 1979), the Rome Convention of 1961, the WIPO Copyright Treaty of 1996, the WIPO Performances and Phonograms Treaty of 1996 and the Universal Copyright Convention (as revised on July 24, 1971). These rights and subject matter take effect in the relevant jurisdiction in which the License terms are sought to be enforced according to the corresponding provisions of the implementation of those treaty provisions in the applicable national law. If the standard suite of rights granted under applicable copyright law includes additional rights not granted under this License, such additional rights are deemed to be included in the License; this License is not intended to restrict the license of any rights under applicable law.