Re: [Caml-list] How to add a hook to Stream.junk?

[Francois Berenger <berenger@riken.jp>]

On 11/21/2012 10:35 AM, Wojciech Meyer wrote:
> bob zhang <bobzhang1988@gmail.com> writes:
>
>> Hi List,
>>     Does anyone know any trick to add a hook to Stream.junk,  I have
>> tried different ways,  but did not find any solution, yet
>> I want to trigger an action each time when I junk a token from the
>> stream. (copy the whole file from stdlib is fine, but I don't
>> know how to make the type checker happy :-()
>> --
>> Regards
>> -- Bob
>
> You can parametrise the Stream.t type with your desired type and the
> hook.
>
> Then you can substitute type using destructive substitution of a type:
>
> module Stream : module type of Stream with type 'elt t := ('hook, 'elt)
> CustomStream.t = Stream
>
> Finally you can implement your own CustomStream.junk function that
> operates on the parametrised type and include the CustomStream module.

Why the need for module type of and all?

Why not simply:

module MyStream = struct
   include Stream
   let junk =
     failwith "put your code here"
end;;

Which I can read as "MyStream is a Stream where I redefined the junk 
operation".

> This should work, but I've not tested or compiled it.
> --
> Wojciech Meyer
> http://danmey.org
>