Question aboutthe use of an inner forall
Mon, 19 Aug 2002 04:09:24 +0200
Still some question: Ok a is a type and Integer is a type . But a can be
instantiated to integer. This comes pretty close to call a therefore a type
----- Original Message -----
From: "Jon Cast" <firstname.lastname@example.org>
To: "Scott J." <email@example.com>
Cc: "Ashley Yakeley" <firstname.lastname@example.org>; <email@example.com>
Sent: Monday, August 19, 2002 3:48 AM
Subject: Re: Question aboutthe use of an inner forall
> "Scott J." <firstname.lastname@example.org> wrote:
> > A question: s is not a type variable as a isn't it? I mean a can be
> > of type Integer while s cannot.
> Guessing at your question:
> a has no type (and neither does s); it /is/ a type. In Haskell, types
> have kinds. And, both a and s have kind *.
> Now then, the user can instantiate a to Integer, yes. And the user
> cannot instantiate s to anything---that's what the `forall' is for.
> runST will (theoretically) instantiate s to something. That could be
> Integer if the language implementors felt like it. The user of runST
> certainly has to be prepared for the possibility.
> Does that come close to answering your question?
> > Regards,
> > Scott
> Jon Cast
> Haskell-Cafe mailing list