From: William Lovas <wlovas@stwing.upenn.edu>
To: caml-list <caml-list@inria.fr>
Subject: Re: [Caml-list] cyclic types
Date: Sun, 30 Jan 2005 02:19:23 -0500 [thread overview]
Message-ID: <20050130071922.GA2798@force.stwing.upenn.edu> (raw)
In-Reply-To: <7f8e92aa050129220540e72c6d@mail.gmail.com>
On Sun, Jan 30, 2005 at 08:05:23AM +0200, Radu Grigore wrote:
> Only one (small) problem remains. I do not understand this:
>
> # type t = t StringMap.t option;;
> The type abbreviation t is cyclic
> # type t = Some of t StringMap.t | None;;
> type t = Some of t StringMap.t | None
The first is a type abbreviation, while the second is a datatype
declaration. They both introduce a new type, in some sense: the first does
so by asserting its equality to some existing type, while the second does
so by defining one or more coercions from existing types to the new type
(i.e. constructors). Only the second can refer to the type being defined
on the right-hand side, for the reasons mentioned earlier.
cheers,
William
next prev parent reply other threads:[~2005-01-30 7:19 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-01-29 12:15 Radu Grigore
2005-01-29 12:34 ` Radu Grigore
2005-01-29 13:42 ` [Caml-list] " Remi Vanicat
2005-01-29 17:12 ` brogoff
2005-01-29 17:33 ` Radu Grigore
2005-01-29 23:47 ` Damien Doligez
2005-01-30 5:56 ` brogoff
2005-01-30 6:05 ` Radu Grigore
2005-01-30 7:19 ` William Lovas [this message]
2005-01-30 10:33 ` Xavier Leroy
2005-01-30 11:44 ` sejourne_kevin
2005-02-01 9:27 ` Christophe Raffalli
2005-01-29 21:02 ` skaller
2005-01-30 6:46 ` brogoff
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