Avoiding "No explicit method ..." warnings

[Simon Peyton-Jones]

Done!

| -----Original Message-----
| From: George Russell [mailto:ger@tzi.de]
| Sent: 21 January 2003 15:43
| To: Simon Peyton-Jones
| Cc: Dean Herington; glasgow-haskell-users@haskell.org
| Subject: Re: Avoiding "No explicit method ..." warnings
|=20
| Simon Peyton-Jones wrote:
| [snip]
| > One other idea though.  Suppose you say
| >
| >     class ComplicatedClass x where
| >         _simpleTitleFn :: x -> String
| >         muchMoreComplicatedTitleFn :: extra arguments -> x -> IO ...
| >
| > In general GHC doesn't report "warning unused" for variables whose
name
| > begin with an underscore.  In the case of class methods, I don't
think
| > it suppresses the warning, but that would be an easy change to make.
| > Indeed, it would arguably be more consistent to do so anyway
| >
| > > #-}) which compiles exactly as normal except that (1) no warning
is
| > > given for instances which don't define it; (2) a warning is given
| > > whenever anyone outside the class declaration *uses*
simpleTitleFn.
| >
| > The "_" idea would achieve (1).  You could get (2) by not exporting
the
| > "_" method from the module defining ComplicatedClasss.
| >
| > How would that be?
| [snip]
| Yes, this looks just as good as my original idea, if not better.
Especially
| as it "would be an easy change to make".
|=20
| In fact there are some cases where I might want to use "simpleTitleFn"
on a
| "Trust me, it's defined for this type" basis, but that could be
achieved by
| exporting an equivalent, but deprecated, function.