Function Application is not Currying

Jon Harrop jon at ffconsultancy.com
Fri Jan 30 20:12:49 CET 2009


I had hoped someone else would correct you but they haven't. So...

Xah Lee wrote:
> Here are some examples of a function that returns a function as
> result, but is not currying.
> 
> Mathematica example:
> 
> f[n_]:=Function[n^#];
> f[7][2]
> (* returns 49 *)
> 
> Emacs lisp example:
> 
> (defmacro f (n) (list 'lambda (list 'x) (list 'expt n 'x) ) )
> (funcall (f 7) 2)
> 
> Perl example:
> 
> sub f {$n=$_[0]; sub { $n ** $_[0]} };
> print &{ f(7) } (2);
> 
> Javascript example:
> 
> function f(n) {return function (x) {return Math.pow(x,n);}; }
> alert (f(7) (2));
> 
> However, the above are not languages that support currying,

That is incorrect. Mathematica, Lisp, Perl and Javascript all support
currying.

> which is a feature that Haskell & Ocaml has.

That is correct. Here is an OCaml equivalent:

  let f =
    fun n ->
      fun m ->
        n ** m

> To be more concrete, in the context of a given computer language, to
> say that it support curring, is to mean that the compiler understand
> the concept to certain degree. More to the point, the language is
> inherently able to take a function of more than one arg and
> deconstruct it to several functions of single arg.

That is incorrect. You only need a language with first-class functions.

I believe you are confusing the syntactic support in OCaml and Haskell for
something more. It simply allows you to rewrite the above as:

  let f n m = n ** m

or:

  let f = fun n m -> n ** n

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/?u



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