Re: [Haskell-cafe] Re: Currying and Partial Evaluation

On Wed, 2008-01-09 at 03:37 +0100, Achim Schneider wrote:

Derek Elkins wrote:

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On Wed, 2008-01-09 at 00:51 +0100, Achim Schneider wrote:

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Fernando Rodriguez wrote:

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Hi,

Is currying in Haskell the same thing as Partial Evaluation (http://en.wikipedia.org/wiki/Partial_evaluation)? Am I getting partial evaluation for free just by using Haskell?

No, currying is this:

No, it is not. This is partial application. See the wiki page Neil referenced.

Which works because of the functions being curried...

and therefore partial application can't be currying. Currying is the operation of turning (a,b) -> c into a -> b -> c. Nothing more.

of course, the usage is to "partly" apply a function, which is not possible, as all Haskell functions are, by default, curried, and thus only have one parameter, which can either be applied or not.

Indeed. Partial application is a fuzzy term. I give a potential objective definition here: http://lambda-the-ultimate.org/node/2266#comment-33620

Partial evaluation, OTOH, goes into the direction of laziness vs. eagerness: Iff the compiler sees that a thunk is only dependent on data known at compile-time, it may choose to evaluate this thunk already at compile-time, if you're lucky and the compiler isn't lazy,

Partial evaluation has little to do with lazy v. eager evaluation.

main = putStrLn $ show $ 1 + 2

might end up being

main = putStrLn "3"

in the object file.