Hi, On Mon, 14 Feb 2005 14:40:56 +0100, Daniel Fischer wrote:
\f g h x y -> f (g x) (h y) ((flip . ((.) .)) .) . (.)
Cool!
But I must say, I find the pointed version easier to read (and define). It certainly is. In fact, I transformed it automatically using a toy lambdabot plugin, i've recently been writing.
So back to the question before this one, is there a definite advantage of point-free style?
I tend to use semi-point-free style, but I might be argued away from that. Yes, me too. I think obscure point-free style should only be used if a type signature makes it obvious what is going on. Occasionally, the obscure style is useful, though, if it is clear there is exactly one function with a specific type, but tiresome to work out the details using lambda expressions. For example to define a map function for the continuation monad cmap :: (a -> b) -> Cont r a -> Cont r b One knows that it must look like cmap f = Cont . foo . runCont where foo is some twisted composition with f, so successively trying the usual suspects ((f.).), ((.f).), ... will finally lead to the only type-checking and thus correct version (.(.f)), even though I can't tell what exactly that does without looking at the type or eta-expanding it.
Thomas