From: Dario Teixeira <darioteixeira@yahoo.com>
To: caml-list@inria.fr, oleg@okmij.org
Subject: Re: [Caml-list] GADTs in OCaml
Date: Sun, 12 Jul 2009 05:56:49 -0700 (PDT) [thread overview]
Message-ID: <468067.61779.qm@web111510.mail.gq1.yahoo.com> (raw)
In-Reply-To: <20090711030510.49092176DE@Adric.metnet.navy.mil>
Hi,
> We present a simple, pure, magic-free implementation of a form of
> GADTs in OCaml that is sufficient for the common applications of GADTs
> such as data structures with embedded invariants, typed printf/scanf,
> tagless interpreters. (...)
Very interesting -- clever, yet so simple! But note that as far as the
link-nodes-shall-not-be-ancestors-of-their-kind problem is concerned, there
is one problem with the presented implementation. Consider the following
declarations:
let t1 = text "ola"
let t2 = href "http"
let t3 = bold [t1; t2]
let t4 = mref "http" [t1]
This causes an error upon t4. The reason is that because of t3, t1 was
unified as "node_link node_t", whereas t4 requires it to be "node_nolink node_t". I think the solution is to revert to using polymorphic variants
for the phantom type, and take advantage of their open-ended nature.
(Though I'm guessing some extra massaging will be required -- it's Sunday
and I don't have much time to look into this).
Anyway, perhaps the Batteries folks will consider including both versions
of the Eq module? It will certainly prove useful for many people. (Am I
correct in assuming you are releasing the code into the public domain or
at least some open-source friendly license?)
Best regards,
Dario Teixeira
next prev parent reply other threads:[~2009-07-12 12:56 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-11 3:05 oleg
2009-07-12 12:56 ` Dario Teixeira [this message]
2009-07-13 12:45 ` [Caml-list] " Edgar Friendly
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