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RE: [Caml-list] Haskell features in O'Caml
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Date: -- (:)
From: Remi VANICAT <vanicat@l...>
Subject: Re: [Caml-list] Haskell features in O'Caml
Christian.Schaller@cert.siemens.de writes:

> > The correct answer might have been a reference to the module system.
> > You can specify the type of a function either in a separate *.mli-file
> > or in an explicit module declaration:
> > 
> > # module M : sig                 
> >     val mul : int -> int -> int  
> >   end = struct                   
> >     let mul a b = a * b          
> >   end;;                          
> > module M : sig val mul : int -> int -> int end
> > # M.mul 2 3;;
> > - : int = 6
> > # module N : sig               
> >     val mul : int -> int -> int
> >   end = struct                 
> >     let mul a b = a *. b (* Arithmetic is monomorphic - no 
> > type classes *)
> >   end;;                        
> > Signature mismatch:
> > Modules do not match:
> > [...]
> > 
> 
>   Unfortunately there seems to be a difference between explicit module
> declaration as seen above and the separation of interface and
> implementation.
> 
>   Since implementation is not automatically checked against the interface
> (or did I get something wrong?),

yes, you do:

test.ml :

let f x = x

test.mli :

val f : int -> float

$ ocamlc -c test.ml
I/O error: test.cmi: No such file or directory
$ ocamlc -c test.mli
$ ocamlc -c test.ml
The implementation test.ml does not match the interface test.cmi:
Values do not match: val f : 'a -> 'a is not included in val f : int -> float



> you just load you implementation (or
> compile it) without using (or compiling) the appropriate interface and there
> will be no complaint about mismatch in signature and structure.
> 
>   I'd prefer the compiler/desktop automatically look for interface
> definition while compiling/loading.
> 
>   One more or less off-topic question about interfaces: is there a way to
> see the all what's inside a module when I'm opening it using "open" (like
> "module M : sig val mul : int -> int -> int end" in above example)?

yes :

$ Module T = List
module T :
  sig
    external length : string -> int = "%string_length"
    external get : string -> int -> char = "%string_safe_get"
    external set : string -> int -> char -> unit = "%string_safe_set"
[...]
    external unsafe_fill : string -> pos:int -> len:int -> char -> unit
      = "fill_string" "noalloc"
  end



-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat
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