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Date: Wed, 6 Jul 2011 09:11:09 +0400 (MSD)
From: malc <av1474@comtv.ru>
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To: Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>
cc: caml-list@inria.fr
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Subject: Re: [Caml-list] Type inference and marshalling

On Wed, 6 Jul 2011, Jacques Garrigue wrote:

> On 2011/07/05, at 22:59, malc wrote:
> 
> > Perhaps someone could explain why following behaves the way it does:
> > 
> > ~$ ocaml
> >        Objective Caml version 3.11.2
> > 
> > # let f ic = let i = input_value ic in let j = i + 1 in LargeFile.seek_in ic i;;
> > Warning Y: unused variable j.
> > val f : in_channel -> unit = <fun>
> 
> The return type of input_value being 'a, which gets generalized by the
> relaxed value restriction, i gets the polymorphic type "forall 'a. 'a".
> So you can use it both as an int and an int64.
> ==> input_value is an unsafe function, you should always write a type
> 	annotation on its return type.

Sure i'm well aware of that, but to me "let j = i + 1" means that i has
type int and after that "LargeFile.seek ic i" makes no sense yet is
accepted by the type checker.

> 
> > # let f ic = let i = input_value ic in let j = i + 1 in LargeFile.seek_in ic j;;
> > Error: This expression has type int but an expression was expected of type
> >         int64
> 
> j being the result of an integer addition, it has type int, and cannot be used
> as int64.
> 
> Jacques
> 
> 

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