[Haskell-cafe] Re: Currying and Partial Evaluation

Derek Elkins wrote:

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

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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.

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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

Yes, it seems kind of obvious that eating a chicken isn't the same as currying a chicken, but then there's a difference between eating a grilled and a curried chicken... and cooking is always more complex than eating. And you just can't have a curried chicken when there's no one around that curries them. So, currying can also be the operation of turning (define (foo x y) (+ x y)) into foo x y = x + y or, mere syntactically, foo x y = x + y into foo = \x -> \y -> x + y

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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.

Well, enough for a thunk to be a reasonable metaphor for a candidate partial evaluation. The compiler is eager, so that the result is memoized before it is used... or not, but then that may not be deducible for the compiler. It's a bit like stop and go traffic. "Opportunistic evaluation" probably fits the concept better than "eager". Can we stop nit-picking, please? -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited.