Re: [Haskell-cafe] Re: The Worker/Wrapper Transformation

On Jan 3, 2008 6:08 AM, Achim Schneider wrote:

Achim Schneider wrote:

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[...]

I'm trying to grok that

[] = id ++ = .

in the context of Hughes lists.

I guess it would stop to slip away if I knew what : corresponds to.

Well, (:) has type a -> [a] -> [a], so a function corresponding to (:) for Hughes lists should have type foo :: a -> H a -> H a that is, foo :: a -> ([a] -> [a]) -> [a] -> [a] so it can be written foo x h = (x:) . h which lambdabot informs me can also be written as (.) . (:). But in the end I'm not sure how helpful that is for understanding Hughes lists! I think the key sentence from the paper is this: "by representing a list xs as the function (xs ++) that appends this list to another list that has still to be supplied." If you understand that sentence, then you can understand why [] is id and (++) is (.). -Brent