Peter Hawkins <hawki...@cs.stanford.edu> writes:
> Hi...
>
> I have a quick question. I want to extend the List module with various
> functions that I want that aren't present in the standard library,
> much as the Batteries ExtList library does.
>
> I might write the following code in "mylibrary.ml":
> module MyList = struct
> include List
> let foo x = ... code here
> let bar y = ... code here
> end
>
> That's ok so far, but now suppose I want to write a "mylibrary.mli"
> interface file corresponding to "mylibrary.ml". Ideally I'd write
> something like this in "mylibrary.mli":
> module MyList : sig
> include List (* unknown module type List *)
> val foo : ...
> val bar : ...
> end
>
> Unfortunately I can't include "List" here since it is a structure, not
> a signature. I don't think there is a way to say "include the
> signature associated with List".
>
> I can think of three solutions:
> a) Copy the complete signature of List into MyList. This is a bad idea
> since the List module might change in the future. This is what the
> Batteries ExtList module does.
> b) Alter the List module to define a signature, say List.S, in
> addition to its other contents. I can't easily do this since I didn't
> write the List module.
> c) Don't write a .mli file at all.
>
> Are there any other alternatives?
Something like :
module MyList = struct
include List
module M : sig val foo : int -> unit end = struct
let foo x = ()
let bar y = y
end
include M
end
and no .mli file. The module M is there to alow you to give (or hide)
the signature of just your extra functions.
> Cheers,
> Peter
MfG
Goswin
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