This is a pretty easy problem.

Using the file:for-each-line to iterate over each line, I increment a variable for each increase. I also leave the most recently read value on the stack for the next comparison.

The variable is initialized to -1. My initial comparison value is 0, so the first data from the file will be greater than this. Using an initial -1 value ensures that the needed adjustment is factored in.

~~~#-1 'Increased var-n 
 
:process (ns-n) s:to-number tuck lt? [ &Increased v:inc ] if ; 
#0 'day1.input [ process ] file:for-each-line drop 
 
@Increased n:put nl 
~~~

The introduction of a three value sliding window makes this a little trickier. I chose to use only a single accumulator variable, keeping the values for the window and the latest sum on the stack.

I use reorder to update the stack orderings when adjusting the values for the sliding window and when moving the newest sum to the bottom.

I'm using the same trick with a negative starting value (-3 in this case) for my count, to allow for the initial non-existant entries of zero.

~~~#-3 'Increased var-n 
 
:slide   'abcde 'cdeacde reorder ; 
:sum     + + ; 
:check   [ lt? [ &Increased v:inc ] if ] sip ; 
:update  'abcd 'dabc reorder ; 
:process s:to-number slide sum check update ; 
 
#0 #0 #0 #0 'day1.input [ process ] file:for-each-line 
drop-pair drop-pair 
 
@Increased n:put nl 
~~~