Hello,
I've been working with alternative versions of these combinators:
each
map
find
subset
When using the "static stack" style, I noticed some common items in
the stack:
( value index seq length )
Another thing in common was words that do these:
Check if the index is out of bounds
Increment the index
Get the ith item in seq and put it at the 'value' location in
the stack.
So I now have a separate vocabulary called 'iter' which has these
words:
----------------------------------------------------------------------
: iter-done? ( value index seq length -- value index seq length ? )
3 npick over >= ; inline
: iter-increment ( value index seq length -- value index seq length )
>r >r 1+ r> r> ; inline
: iter-get ( value index seq length -- value index seq length )
>r rot drop 2dup >r >r nth-unsafe r> r> r> ; inline
----------------------------------------------------------------------
I then rewrote the combinators in terms of these. In each case I have
a "run" word which is the workhorse word. It's also the
self-documenting sweet-spot word. Here are the run words for the
combinators:
----------------------------------------------------------------------
: each-run ( pred val i seq len -- )
iter-done? [ each-done ] [ iter-get each-call iter-increment each-run ]
if ; inline
: map-run ( newseq q val i seq len -- newseq )
iter-done? [ map-done ] [ iter-get map-call map-set iter-increment map-run ]
if ; inline
: find-run ( quot value i seq len -- i value )
{ { [ iter-done? ] [ find-not-found ] }
{ [ iter-get find-test ] [ find-found ] }
{ [ t ] [ iter-increment find-run ] } } cond ; inline
: subset-run ( acc quot value i seq len -- subseq )
{ { [ iter-done? ] [ subset-done ] }
{ [ iter-get subset-match? ] [ subset-push iter-increment subset-run ] }
{ [ t ] [ iter-increment subset-run ] } } cond ; inline
----------------------------------------------------------------------
All of these words have good performance.
Of course, each combinator has it's own helper words and a "setup"
word which sets up the static stack.
Stack masters recommend keeping the stack short. The reason is because
long stacks can be hard to think about. However, a long but static
stack, is easy to deal with.
There are a few guidelines put forth by the masters of stack
programming. I claim that long but static stacks are an exception
to the guideline of short stacks.
Ed
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