From: Radu Grigore <radugrigore@gmail.com>
To: Goswin von Brederlow <goswin-v-b@web.de>
Cc: Andreas Rossberg <rossberg@mpi-sws.org>, caml-list@yquem.inria.fr
Subject: Re: [Caml-list] mutable and polymorphism
Date: Wed, 15 Sep 2010 20:38:12 +0100 [thread overview]
Message-ID: <AANLkTimdJ7De5FhG=EsG=Tv83msUzMkV_AYhnCHjx=4x@mail.gmail.com> (raw)
In-Reply-To: <878w32g6wh.fsf@frosties.localdomain>
On Wed, Sep 15, 2010 at 8:10 PM, Goswin von Brederlow <goswin-v-b@web.de> wrote:
> In your original a.ml you didn't use the [...]
Let me rephrase. IMO, both the modified a.ml and the modified c.ml
fail for the same reason: polymorphic references. Therefore, just as
you can't infer from "modified a.ml fails" that "original a.ml should
fail" you can also *not* infer from "modified c.ml fails" that
"original c.ml should fail".
> Because the compiler is stupid and things with a ref can't
> polymorphic.
The compiler isn't stupid: Polymorphic references are unsound. See for
example Section 2.2.3 here:
http://caml.inria.fr/pub/docs/u3-ocaml/ocaml-core.html#toc8
> let f y = let x = ref () in (fun y -> ()) y in f 1; f 'a'
This has different semantics. Consider
let f y = let x = ref 0 in (fun y -> incr x) y in f 1; f 'a'
In any case, I'm more interested in an explanation of what happens,
since in practice I'm quite happy with a.ml (together with hiding the
reference from outside by not putting it in mli).
regards,
radu
next prev parent reply other threads:[~2010-09-15 19:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-15 17:10 Radu Grigore
2010-09-15 17:40 ` [Caml-list] " Andreas Rossberg
2010-09-15 17:59 ` Radu Grigore
2010-09-15 19:10 ` Goswin von Brederlow
2010-09-15 19:38 ` Radu Grigore [this message]
2010-09-15 20:44 ` Kaustuv Chaudhuri
2010-09-17 7:31 ` Goswin von Brederlow
2010-09-17 14:04 ` Radu Grigore
2010-09-17 14:08 ` Radu Grigore
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