English version
Accueil     À propos     Téléchargement     Ressources     Contactez-nous    

Ce site est rarement mis à jour. Pour les informations les plus récentes, rendez-vous sur le nouveau site OCaml à l'adresse ocaml.org.

Browse thread
[Caml-list] 'should have type unit' warning in 'let _ =' ?
[ Home ] [ Index: by date | by threads ]
[ Search: ]

[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
Date: -- (:)
From: Jacques Garrigue <garrigue@k...>
Subject: Re: [Caml-list] 'should have type unit' warning in 'let _ =' ?
From: Richard Jones <rich@annexia.org>
> On Tue, Jul 15, 2003 at 10:04:36AM +0900, Jacques Garrigue wrote:
> > By the way, there is a reason "let _ =" produces no warning: this is
> > the only way to do a partial application without warning.
> > "expr; ..." and even "ignore (expr); ..." will produce a warning.
> Interesting ... what's the use of a partial application which is
> then ignored?

The same as all application whose result is ignored: side effects.
I know this is quite rare. (I can remember using this only once.)
But it would be disturbing to make it completely impossible.

Or is it not so important?
Actually I wonder whether it would not be safer to simply warn for all
unused partial applications in a compiled program. This is a bit
subtle, as one has to keep track of unused variables too (functions
defined by partial application which are never used).

A middle ground would be to only warn when the wild pattern matches a
function type, assuming that when you name something you know what
you are doing. This would be mostly compatible: you just have to name
the pattern when you want to discard a function. As a nice aside, it
would avoid most uses of "ignore".

By the way, my personal approach would be to let programers declare what
they want: remove the "should be unit" warning (it can be easily
enforced by "let () = ... in"), and remove all warnings on "ignore",
since you could then write "let _ = ... in" if you want the partial
application warning. But this is maybe expecting too much from


Jacques Garrigue

To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners