Re: curried fns
 cheno@m...
[
Home
]
[ Index:
by date

by threads
]
[ Message by date: previous  next ] [ Message in thread: previous  next ] [ Thread: previous  next ]
[ Message by date: previous  next ] [ Message in thread: previous  next ] [ Thread: previous  next ]
Date:  19951121 (10:50) 
From:  cheno@m... 
Subject:  Re: curried fns 
Jocelyn Serot wrote : >>Hello, >> >>Could someone please explain the difference(s) between: >> >> let f x = function y > y + x;; >> >>and >> >> let f x y = 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 = let z = 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 = let z = 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 !) For my example : #let fact x = print_int x ; print_newline() ; x ;; fact : int > int = <fun> first version #let h1 x = let z = fact x in function y > y + z ;; h1 : int > int > int = <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 = h1 30 ;; 30 a1 : int > int = <fun> Now, a1 is all defined : no more print ... the function a1 don't print anything #map a1 [1 ; 2 ; 3] ;;  : int list = [31; 32; 33] second version #let h2 x y = let z = fact x in y + z ;; h2 : int > int > int = <fun> there is no call for fact : you have specialized the first (and not last) argument of h2 #let a2 = h2 30 ;; a2 : int > int = <fun> now the evaluation is complete, and there is calls for print_int #map a2 [1 ; 2 ; 3] ;; 30 30 30  : int list = [31; 32; 33] # Laurent Chéno  Laurent CHENO teaching at / enseignant au Lycée LouisleGrand  123 rue SaintJacques 75231 PARIS CEDEX 05  FRANCE personal phone (33) 1 48 05 16 04  fax (33) 1 48 07 80 18 