ghc warnings messed up in 6.01

[Simon Peyton-Jones]

Done, I believe.  It'll be in the next release (6.3/6.4).

Simon

| -----Original Message-----
| From: glasgow-haskell-users-bounces at haskell.org
[mailto:glasgow-haskell-users-
| bounces at haskell.org] On Behalf Of Mike Gunter
| Sent: 07 December 2003 16:50
| To: glasgow-haskell-users at haskell.org
| Subject: Re: ghc warnings messed up in 6.01
| 
| 
| Simon seems to have agreed that The Right Thing is to treat bindings
| with names beginning with an underscore as if they are used w.r.t. to
| the bindings they use (they're already treated as used w.r.t. warnings
| for themselves.)  With this enhancement (and the other warning fixes
| apparently already in HEAD), you should be able to change "ds" to
| "_ds" and get no warnings.
| 
| BTW (here's the real point of my message :-)), is this enchancement
| planned?  For when?  Thanks.
| 
| 	mike
| 
| 
| > has anyone else noticed that the warnings generated by ghc appear to
| > have become quite incorrect in many cases?
| >
| > in particular, the 'defined but not used' warning is generated
| > spuriously a lot. almost as if it is being checked after dead code
| > elimination and desugaring of some sort..
| >
| > here is an example which touches all the reproducable bugs I have
found.
| >
| >> module Main(main) where
| >> import List(nub)
| >> import Monad()
| >>
| >> as = repeat 'a'
| >> bs = repeat 'b'
| >> ds = nub as
| >>
| >> cs = [(a,b) | a <- as | b <- bs]
| >>
| >> main = print $ take 10 cs
| >
| >
| > ;ghc -W -fglasgow-exts  Foo.hs
| >
| > Foo.hs:1:
| >     Warning: Module `List' is imported, but nothing from it is used
| >              (except perhaps instances visible in `List')
| >
| > Foo.hs:1:
| >     Warning: Module `Monad' is imported, but nothing from it is used
| >              (except perhaps instances visible in `Monad')
| >
| > Foo.hs:7: Warning: Defined but not used: ds
| >
| > Foo.hs:9: Warning: Defined but not used: b
| >
| > Foo.hs:9: Warning: Defined but not used: a
| >
| >
| > notice:
| >
| > 1) it claims nothing is used by List, when 'nub' definatly is being
| > used. (technically true, since ds is not used, but this warning is
more
| > confusing than anything. my first inclination is to delete the
import
| > line, causing the program to fail to compile, the only fix seems to
be
| > to track down the root by hand)
| >
| > 2) it claims Monad is unused, when I specifically imported it with
()
| > meaning I don't want any names from it. (i.e., I just want
instances)
| >
| > 3) defined but not used 'ds': yay! the only valid warning.
| >
| > 4,5) variables bound in parallel list comprehensions always seem to
| > generate warnings.
| >
| >
| > AFAIK, none of these were problems in earlier versions of ghc, they
are
| > quite anoying as they obscure valid warnings. my guess is some
| > desugarings and warning passes were accidentally switched around..
| > problem 1 is particularly bad, since a single unused toplevel could
| > cascade to generating a ton of warnings, all of which must be sorted
| > through to find the actual cause. the others are just anoying as
there
| > doesn't seem to be a workaround short of disabling warnings.
| >
| >         John
| > --
| >
------------------------------------------------------------------------
---
| > John Meacham - California Institute of Technology, Alum. -
john at foo.net
| >
------------------------------------------------------------------------
---
| > _______________________________________________
| > Glasgow-haskell-users mailing list
| > Glasgow-haskell-users at haskell.org
| > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
| _______________________________________________
| Glasgow-haskell-users mailing list
| Glasgow-haskell-users at haskell.org
| http://www.haskell.org/mailman/listinfo/glasgow-haskell-users