[Haskell-cafe] Re: Currying and Partial Evaluation
Achim Schneider
barsoap at web.de
Tue Jan 8 18:51:55 EST 2008
Fernando Rodriguez <frr149 at easyjob.net> 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:
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.
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