From: Jean-Christophe Filliatre <filliatr@lri.fr>
To: aXl <krauth@fmi.uni-passau.de>
Cc: caml-list@inria.fr
Subject: Re: Typing-problem
Date: Mon, 31 May 1999 12:37:39 +0200 (MEST) [thread overview]
Message-ID: <14162.26227.300552.10117@pc89.lri.fr> (raw)
In-Reply-To: <Pine.GSO.3.96.990530171304.16161A-100000@kosh>
> why is in the following example b of type "string -> string" ?
>
> let a = id id;;
> let b = a;;
> a "foo";;
> (* until here it's covered by the faq's *)
> b;;
It is because:
1. the type variable is not generalized is the type of a;
(it is '_a -> '_a)
2. that type variable is shared between the types of a and b
Therefore when applying a to "foo", that type variable is instanciated
by string, which instanciates also the type of b.
A more detailed explanation is given here :
http://caml.inria.fr/FAQ/FAQ_EXPERT-eng.html#polymorphisme
Best regards,
--
Jean-Christophe FILLIATRE
mailto:Jean-Christophe.Filliatre@lri.fr
http://www.lri.fr/~filliatr
next prev parent reply other threads:[~1999-06-01 15:13 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-05-30 15:24 Typing-problem aXl
1999-05-31 10:37 ` Jean-Christophe Filliatre [this message]
1999-05-31 12:42 ` Typing-problem hubert.fauque
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