From: Andreas Rossberg <rossberg@ps.uni-sb.de>
To: John Skaller <skaller@maxtal.com.au>
Cc: caml-list@inria.fr
Subject: Re: Constructor/reference bug?
Date: Thu, 12 Aug 1999 13:25:53 +0200 [thread overview]
Message-ID: <37B2AF41.3894ABCE@ps.uni-sb.de> (raw)
In-Reply-To: <3.0.6.32.19990811180530.00985e40@mail.triode.net.au>
John Skaller wrote:
>
> let g x =
> let lineno = ref (1,"") in
> let rec f x' = match x' with
> | NEWLINE p :: t -> lineno := p; f t
> | COLON :: t -> CTRL !lineno :: f t
> | h :: t -> h :: f t
> | [] -> []
> in f x;;
>
> The code doesn't work as I expected: every
> CTRL value refers to the same lineno, the last one.
Evaluation order of application is not specified in OCaml: arguments may
be evaluated in any order (in fact, byte code does it right-to-left,
native code left-to-right, if I remember correctly). That seems to be
what's happening here: (f t), the second argument to ::, is evaluated
before (CTRL !lineno). Using let eliminates this problem.
HTH,
- Andreas
--
Andreas Rossberg, rossberg@ps.uni-sb.de
:: be declarative. be functional. just be. ::
next prev parent reply other threads:[~1999-08-12 14:42 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-08-11 8:05 John Skaller
1999-08-12 10:51 ` Nicolas Ollinger
1999-08-12 11:22 ` Jean-Christophe Filliatre
1999-08-12 11:25 ` Andreas Rossberg [this message]
1999-08-12 12:16 ` Markus Mottl
1999-08-12 12:05 Damien Doligez
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