Re: [Caml-list] A strange typing error with polymorphic variants

[Vincent Aravantinos <vincent.aravantinos@gmail.com>]

Le 27 oct. 09 à 19:24, Jake Donham a écrit :

> On Tue, Oct 27, 2009 at 3:28 AM, Marc de Falco <marc@de-falco.fr>  
> wrote:
>> The following code :
>> type 'a p = R of 'a t | E of float
>>     and 'a t = { mutable p : 'a p; c : 'a }
>> let f =
>>     let x = sqrt(2.0) in
>>     fun () -> { c = `A; p = E 0.0 }
>>
>> generates the error :
>>   The type of this expression, unit -> _[> `A ] t,
>>   contains type variables that cannot be generalized
>>
>> but if I change the x definition to "let x = 2.0 in" then it works.
>
> I think this is just the value restriction. The type of f is
> generalized only if the right hand side is a value (rather than an
> expression needing some computation); in your examples the one that
> fails is not a value, the others are. It looks like there is a
> relaxation to allow let bindings which are themselves values.

With the -dlambda option, the "sqrt(2.0)" version gives:
   (let
     (f/92
        (let (x/93 (caml_sqrt_float 2.0))
          (function param/94 (makemutable 0 [1: 0.0] 65a))))

whereas the "2.0" version gives:
   (let (f/96 (let (x/97 2.0) (function param/98 (makemutable 0 [1:  
0.0] 65a))))

i.e. this last version is inlined.

I thought the yping was done before (??)

V.