Re: [Caml-list] Type inference question

[Andreas Rossberg <rossberg@ps.uni-sb.de>]

Mark Shinwell wrote:
> 
> However, in the Marshal example above, we have
> 
> 	Marshal.from_channel stdin []
> 
> in the first part of the "let".  In the SML terminology, this is not a
> "nonexpansive expression"[*] (unlike "fun x -> x").  Therefore, I would
> have thought that the appearance of such an expression here would
> prohibit generalisation (in order to prevent possible unsoundness in the
> presence of mutable state).  This is presumably not the case in OCaml:
> can someone explain why?

Recent versions of OCaml employ a slightly relaxed variant of the value 
restriction that allows generalising of variables in covariant position, 
because that is always safe.

Cheers,

   - Andreas

-- 
Andreas Rossberg, rossberg@ps.uni-sb.de

Let's get rid of those possible thingies!  -- TB