Re: [stack] Barebone implementation of concatenative language in c or c++

On Wed, 19 May 2010 11:57:21 -0500, <[email protected]> wrote:

> Even if your language is eager and you're not considering parallel
> combinators, there are still benefits to the applicative approach. In
> particular, you can reduce and transform 'f x' in strictness-preserving
> ways without worrying about the arity of 'g x'. This is useful when
doing
> algebraic manipulation of programs regardless of your evaluation
mechanism.

Final clarification. I mean you can apply rules like this without
consideration for arity and coarity:

  cross f g . bi h i  ==  cross (f . h) (g . i)
    where bi f g x = (f x, g x)
          cross f g x y = (f x, g y)

This is equivalent to a rule like the following in Joy except for the fact
that, of course, this rule isn't remotely valid:

  [H] [I] bi [F] [G] bi*  ==  [H F] [I G] bi*
    where [F] [G] bi = [keep] dip i
          [F] [G] bi* = [dip] dip i

It is, however, valid if all functions have a stack effect of ( x -- x ).
Because the functions in the applicative version aren't lifted to operate
on a stack, you don't have this issue.

- jn