Re: [Caml-list] Function call with a list of parameters

[Bruce Hoult <bruce@hoult.org>]

At 2:59 PM -0800 11/12/01, Chris Hecker wrote:
>  >I'm trying to construct a function which take two arguments :
>>                 Arg1 : a function, Arg2 : a list of parameters for the Arg1.
>>This function will call the function in Arg1 with Arg2 as parameters.
>
>This is slightly related to a feature I'd like that's easy to do in 
>lisp, but I don't think there's a way to do it in ML-style languages:
>
>I have a function that returns a tuple, and a function that takes 
>two curried parameters.  I'd like to pass the results of the first 
>to the second, without having to break up the tuple with fst and snd 
>(or pattern matching).
>
>let f () = (1,2)
>let g x y = x + y
>
>g (? f ())
>
>vs.
>
>let x,y = f () in
>g x y
>
>With lisp you can just "apply" and it works.  There's no way in caml 
>to spread the arguments into a curried function application, however.

No, that's not the case.  "Apply" needs a list, but multiple valued 
function result is NOT a list.  It will be treated by "apply" as 
being just the first value.

bruce@k7:~ > cmucl
CMU Common Lisp 18c, running on k7
Send questions and bug reports to your local CMU CL maintainer,
or to cmucl-help@cons.org. and cmucl-imp@cons.org. respectively.
Loaded subsystems:
     Python 1.0, target Intel x86
     CLOS based on PCL version:  September 16 92 PCL (f)
* (defun f () (values 1 2))

F
* (defun g (x y) (+ x y))

G
* (apply #'g '(1 2))

3
* (apply #'g (f))

Type-error in KERNEL::OBJECT-NOT-LIST-ERROR-HANDLER:  1 is not of type LIST


I'm not quite sure off the top of my head the correct thing to do in 
Common Lisp, but it will be similar to the Dylan:

    define function f() values(1, 2) end;
    define function g(x, y) x + y end;

    let (#rest results) = f();
    apply(g, results);


Ah, here we go, in Common Lisp.  Either...

    (apply #'g (multiple-value-list (f)))

... or ...

    (multiple-value-call #'g (f))


Hope this helps.

-- Bruce
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