Re: [stack] map fusion

John Nowak <[email protected]> wrote:
> Unfortunately, this is not valid because 'F' and 'G' can access more
> than one value on the stack. Here is a counterexample to the above rule:

Okay, I think I get this. (I certainly agree.)

> This seems to be yet another argument against n-ary combinators where
> the quotation is not called a fixed number of times.

_This_ I don't understand. What does that mean?

I would have said "this is an argument against combinators which
repeatedly call function inputs that do not have a statically known
stack effect." Am I being too restrictive? Are you being too
restrictive?

> It seems the solution is to offer two versions of certain combinators.
> The restricted versions ('map, 'each', etc) will be easier to reason
> about and optimize, while the unrestricted versions ('map*', 'each*',
> etc) will remain useful in a way only possible in stack-based
> languages. I think this would be worthwhile to adopt in both typed and
> untyped languages.

I definitely like this; although of course in Factor the asterisk
prefix is already taken.

> - John

-Wm