Message-Id: <v01520c01acd67e5be62c@[194.51.75.132]>
Date: Mon, 20 Nov 1995 20:51:56 +0200
To: caml-list@margaux.inria.fr
From: cheno@micronet.fr (Laurent CHENO)
Subject: Re: curried fns
Jocelyn Serot wrote :
>>Hello,
>>
>>Could someone please explain the difference(s) between:
>>
>> let f x =3D function y -> y + x;;
>>
>>and
>>
>> let f x y =3D y + x;;
>>
>>Both have the same type (int -> int -> int) but they seem to behave
>>distinctly wrt evaluation strategy.
>>
>>For instance, if i use the 1st form and write:
>>
>> let h x =3D let z =3D fact x in fun y -> y + z;;
>> map (h 30) [1;2;3];; (* note 1 *)
>>
>>fact 30 gets evaluated only once (partial evaluation), while
>>the use of the 2nd form for the h function:
>>
>> let h x y =3D let z =3D fact x in y + z;;
>> map (h 30) [1;2;3];;
>>
>>causes fact 30 to be evaluated _for each_ element of the list.
>>
>>Is this normal or do i misunderstand sth about curryfied fns ?..
>>
>>Thanks for any help
1. excuse my poor english, thank's
2. I think this can help (I hope so !)
=46or my example :
#let fact x =3D print_int x ; print_newline() ; x ;;
fact : int -> int =3D <fun>
first version
#let h1 x =3D
let z =3D fact x
in
function y -> y + z ;;
h1 : int -> int -> int =3D <fun>
NB : the result of h1 30 is a function, which has been evaluated in a
environment where
z yields for the result of fact 30
So, we can see the result of print_int in *this* call !
#let a1 =3D h1 30 ;;
30
a1 : int -> int =3D <fun>
Now, a1 is all defined : no more print ... the function a1 don't print anyth=
ing
#map a1 [1 ; 2 ; 3] ;;
- : int list =3D [31; 32; 33]
second version
#let h2 x y =3D
let z =3D fact x
in
y + z ;;
h2 : int -> int -> int =3D <fun>
there is no call for fact : you have specialized the first (and not last)
argument of h2
#let a2 =3D h2 30 ;;
a2 : int -> int =3D <fun>
now the evaluation is complete, and there is calls for print_int
#map a2 [1 ; 2 ; 3] ;;
30
30
30
- : int list =3D [31; 32; 33]
#
Laurent Ch=E9no
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