Hello, what Reid says is exactly right---the issue is not really about what instances are present, the problem is that GHC can't determine how to instantiate `t0`. Perhaps a more direct way to describe this is as follows:
Failed to infer type `t0` while solving constraint `Data.String.IsString (t0 Char)` arising from the use of: elem :: a -> t0 a -> Bool -Iavor On Mon, Aug 3, 2015 at 9:47 AM, Brandon Allbery <allber...@gmail.com> wrote: > On Mon, Aug 3, 2015 at 12:45 PM, Daniel Bergey <ber...@teallabs.org> > wrote: > >> I thought GHC would infer the type when only one instance is in scope, >> at least in some cases, like IsString. But I could well be wrong about >> that. >> > > Typeclasses are open-world; this is not a safe assumption, since instances > are global and an instance added elsewhere at some point in the future > could therefore break your program. > > -- > brandon s allbery kf8nh sine nomine > associates > allber...@gmail.com > ballb...@sinenomine.net > unix, openafs, kerberos, infrastructure, xmonad > http://sinenomine.net > > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > >
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