Re: [Caml-list] optional functions in modules

[Gabriel Scherer <gabriel.scherer@gmail.com>]

You can regain that polymorphism at a moderate efficiency cost by eta-expanding:

   let mmap2 f = match mmap with | None -> failwith "Nope" | Some x -> x f;;
   val mmap2 : ('a -> 'b) -> 'a list -> 'b list = <fun>

On Fri, May 18, 2012 at 5:24 PM, David Rajchenbach-Teller
<David.Teller@ens-lyon.org> wrote:
> On 5/17/12 7:43 PM, Yitzhak Mandelbaum wrote:
>> Thanks to everyone who responded.  FWIW, I found the argument in favor of options most compelling as a general approach.
>>
>> Yitzhak
>>
>
> Note that there is a drawback to that approach: loss of polymorphism.
>
> # let mmap = Some List.map;;
> val mmap : (('a -> 'b) -> 'a list -> 'b list) option = Some <fun>
>
> # let mmap2 = match mmap with | None -> failwith "Nope" | Some x -> x;;
> val mmap2 : ('_a -> '_b) -> '_a list -> '_b list = <fun>
>
> I suspect that first-class modules can help here, but I have not really
> had time to toy with them yet.
>
> Cheers,
>  David
>