Re: [stack] language hierarchy

John Nowak <[email protected]> wrote:
> William Tanksley, Jr wrote:

> > Hmm. Okay, I think I get it. Review: composable means that function
> > composition is available and capable of forming interesting programs.
> > Concatenative means that function composition is the default operation
> > (performed by merely concatenating functions).

> No, not quite. Composable means composing functions is the only way to
> write programs.

Okay, sorry. You might want to choose a different word form then...
the suffix "-able" means that the action is possible, not that it's
mandatory. Perhaps "compository" or "compositional"?
http://plato.stanford.edu/entries/compositionality/ (already taken,
but not in programming).

> Joy works this way. Concatenative languages are
> composable languages with Joy-style syntax. I do not know of any
> language that is composable and not also concatenative; It's the
> obvious syntax to use. However, you can imagine such languages fairly
> easily.

So "concatenative" in your definition refers ONLY to the syntax of a
composable language! Interesting. Perhaps Chris is right, and your
definition of "concatenative" could apply to non-composable languages
as well.

> >> I don't think there's anything composable about Haskell, strictly
> >> speaking. The compose operator in Haskell is really just a function
> >> with infix syntax that operates on functions /as values/ via function
> >> application.

> > Perhaps, but the language supports that composition on such a
> > fundamental level that it's hard to identify it as NOT part of its
> > syntax.

> It isn't any more part of the syntax than 'apply' is part of Cat's
> syntax.

Apply doesn't have special syntax support in Cat. The composition
operator has special syntax support in Haskell.

> > A number of different subsets of Haskell can be constructed
> > that form a composable language -- for example, consider a stack
> > monad. At least if I'm reading your definition of 'composable'
> > correctly.

> No, I don't think you are. The compose function in haskell operates on
> values via application, not on functions directly as it does in Joy.
> Haskell is a functional language, not a function-level language like FL.

When you're looking at a Haskell program which uses composition
exclusively, can you tell it's not actually "composable"? I would say
that there are subsets of Haskell which are composable, just as there
are subsets of Joy which are not (for example, function definition).

> >> This is something you can add to most any vaguely
> >> functional language:
> >>        (define (compose f g) (lambda args (f (apply g args))))

> > Sure; and if you can define that as infix, your language has
> > superficial support for composability.

> Neither infixness, nor any other syntax-related feature, has anything
> to do with my definition of 'composable'.

All features of a language are syntax-related.

> - John

-Wm