proposal #2254: have Control.Arrow re-export (>>>) and (<<<)

[Simon Peyton-Jones]

Aha.  So now it's unclear what the desired behaviour is.  Do we want a warning for import statements that can be deleted altogether?  If not, I can easily remove it!  Or is it just the wording of the warning that is bad?

S

| -----Original Message-----
| From: libraries-bounces at haskell.org [mailto:libraries-bounces at haskell.org] On Behalf Of Ross Paterson
| Sent: 02 May 2008 09:10
| To: libraries at haskell.org
| Subject: Re: proposal #2254: have Control.Arrow re-export (>>>) and (<<<)
|
| On Fri, May 02, 2008 at 08:30:03AM +0100, Simon Peyton-Jones wrote:
| > | Generally, if module A exports foo, module B imports A and re-exports
| > | foo, and module C imports both A and B, there should be no ambiguity.
| > | Not even if it reexports all of modules A and B. Why would e.g. GHC
| > | need to warn in that case?
| >
| > Perhaps Niklas can say whether #1148 is the bug he is describing, and if not file a new one?
|
| Niklas's example:
|
|         module A where
|         foo x = x
|
|         module B(foo) where
|         import A
|
|         module C where
|         import A
|         import B
|         c = foo 'a'
|
| ghc -W says
|
| C.hs:2:0:
|     Warning: Module `A' is imported, but nothing from it is used,
|                except perhaps instances visible in `A'
|              To suppress this warning, use: import A()
|
| It's true that the import can be deleted, but not that "nothing from it
| is used".
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