A strange typing error with polymorphic variants

Marc de Falco

Jake Donham
 Vincent Aravantinos

Jake Donham
[
Home
]
[ Index:
by date

by threads
]
[ Message by date: previous  next ] [ Message in thread: previous  next ] [ Thread: previous  next ]
[ Message by date: previous  next ] [ Message in thread: previous  next ] [ Thread: previous  next ]
Date:  20091027 (18:38) 
From:  Vincent Aravantinos <vincent.aravantinos@g...> 
Subject:  Re: [Camllist] A strange typing error with polymorphic variants 
Le 27 oct. 09 à 19:24, Jake Donham a écrit : > On Tue, Oct 27, 2009 at 3:28 AM, Marc de Falco <marc@defalco.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.