Re: [Haskell-cafe] Functions are first class values in C

On Sat, 22 Dec 2007, Cristian Baboi wrote:

On Sat, 22 Dec 2007 16:55:08 +0200, Miguel Mitrofanov wrote:

...

...

...

...

In Haskell I cannot pass a function to a function, only its expansion.

...

What do you mean by "expansion"? Can you clarify this?

f1=\x->x+1 f2=\x->2*x g=\x->x.f1 h=\x->x.(\x->x+1)

h is g

Not clear. Try starting with "function's expansion is..."

function's expansion is ... just like macro expansion.

No, it's not. Expanding variables (swapping f1 for \x->x+1) isn't the evaluation mechanism in haskell, g and h really are semantically equivalent values and we can't do actual computation just by expanding variables. Whereas expanding a macro is equivalent to beta-reduction (evaluating a function application), which isn't required before passing something in Haskell. We pass functions, not just their results. Here's a trivial example that does so: (\x -> x) (\x -> x) A lambda calculus classic that doesn't typecheck in Haskell: (\x -> x x) (\x -> x x) Feel free to try evaluating it! -- flippa@flippac.org "I think you mean Philippa. I believe Phillipa is the one from an alternate universe, who has a beard and programs in BASIC, using only gotos for control flow." -- Anton van Straaten on Lambda the Ultimate