By all means make the proposal -- I like this idea. > On Oct 3, 2016, at 4:29 AM, Herbert Valerio Riedel <hvrie...@gmail.com> wrote: > > Hi *, > > I seem to recall this was already suggested in the past, but I can't > seem to find it in the archives. For simplicity I'll restate the idea: > > > foo :: Int -> Int -> (Int,Int) > foo x y = (bar x, bar y) > where > bar x = x+x > > results merely in a name-shadowing warning (for -Wall): > > foo.hs:4:9: warning: [-Wname-shadowing] > This binding for ‘x’ shadows the existing binding > bound at foo.hs:2:5 > > > However, > > import Data.Monoid > > (<>) :: String -> String -> String > (<>) = (++) > > main :: IO () > main = putStrLn ("Hi" <> "There") > > doesn't allow to shadow (<>), but rather complains about ambiguity: > > bar.hs:7:23: error: > Ambiguous occurrence ‘<>’ > It could refer to either ‘Data.Monoid.<>’, > imported from ‘Data.Monoid’ at bar.hs:1:1-18 > or ‘Main.<>’, defined at bar.hs:4:1 > > > This is of course in line with the Haskell Report, which says in > https://www.haskell.org/onlinereport/haskell2010/haskellch5.html#x11-1010005.3 > > | The entities exported by a module may be brought into scope in another > | module with an import declaration at the beginning of the module. The > | import declaration names the module to be imported and optionally > | specifies the entities to be imported. A single module may be imported > | by more than one import declaration. Imported names serve as top level > | declarations: they scope over the entire body of the module but may be > | shadowed by *local non-top-level bindings.* > > > However, why don't we allow this to be relaxed via a new language > extensions, to allow top-level bindings to shadow imported names (and > of course emit a warning)? > > Unless I'm missing something, this would help to keep existing and > working code compiling if new versions of libraries start exporting new > symbols (which happen to clash with local top-level defs), rather than > resulting in a fatal name-clash; and have no major downsides. > > If this sounds like a good idea, I'll happily promote this into a proper > proposal over at https://github.com/ghc-proposals/ghc-proposals; I > mostly wanted to get early feedback here (and possibly find out if and > where this was proposed before), before investing more time turning > this into a fully fledged GHC proposal. > > Cheers, > HVR > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
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