From: Keith Wansbrough <Keith.Wansbrough@cl.cam.ac.uk>
To: Alex Baretta <alex@barettadeit.com>
Cc: Ocaml <caml-list@inria.fr>
Subject: Re: [Caml-list] Fragile pattern matching?!
Date: Mon, 28 Feb 2005 10:32:26 +0000 [thread overview]
Message-ID: <E1D5iCQ-0001qB-00@mta1.cl.cam.ac.uk> (raw)
In-Reply-To: Your message of "Mon, 28 Feb 2005 11:17:02 +0100." <4222EF9E.1030106@barettadeit.com>
Alex Baretta writes:
> let to_int value = match value with
> | Int x -> x
> | _ -> raise Some_exception
>
> The compiler signals a warning for a fragile pattern matching at the "_"
> character.
>
> Why in the world should this code signal such a warning?
The reason is to do with code maintenance. When in future you add
another constructor to the value type, the type checker will tell you
the locations of all matches that have now become incomplete, so that
you can fix them. But the match in "to_int" above will never become
incomplete. If the type checker passed this silently, then a bug
could easily be introduced. Hence the warning.
HTH.
--KW 8-)
next prev parent reply other threads:[~2005-02-28 10:32 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-02-28 10:17 Alex Baretta
2005-02-28 10:32 ` Keith Wansbrough [this message]
2005-02-28 10:35 ` [Caml-list] " Alex Baretta
2005-02-28 10:39 ` Luc Maranget
2005-02-28 10:49 ` Alex Baretta
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