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

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

Fernando Rodriguez wrote:

...

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.

Prelude> let f x y = 1 + x * ( y - 3 ) Prelude> let g = f 1 Prelude> let h = f 2 Prelude> g 1 -1 Prelude> g 2 0 Prelude> h 1 -3 Prelude> h 2 -1

or, a bit more confusing and possibly enlightening,

Prelude> let y f = f $ y f Prelude> :t y y :: (b -> b) -> b Prelude> let fixpoint f n = if n <= 1 then 1 else n * (f $ n - 1) Prelude> :t fixpoint fixpoint :: (Num b, Ord b) => (b -> b) -> b -> b Prelude> let fac = y fixpoint Prelude> :t fac fac :: Integer -> Integer Prelude> fac 10 3628800

Prelude> fac 100 9332621544394415268169923885626670049071596826438162146859296389521759999 3229915608941463976156518286253697920827223758251185210916864000000000000 000000000000

Note that "fixpoint 3" won't work, and that's good.