That does seem odd. Can you give instructions for how to reproduce this? The fewer dependencies the better :-)
Simon From: [email protected] [mailto:[email protected]] On Behalf Of Carter Schonwald Sent: 17 August 2012 19:01 To: GHC Users List Subject: funny type inference error with ghc7.6rc1 Hey All, When playing with the current hackage versions of Epic and Idris to make them play nice with ghc7.6rc1 http://hackage.haskell.org/package/idris-0.9.2.1 and http://hackage.haskell.org/package/epic-0.9.3 (current version on github now builds on ghc 7.6, https://github.com/edwinb/EpiVM) I ran into some funny type inference problems. Namely, using the idris-0.9.2.1 source and iteratively seeing how ghc complains, I repeated found that ghc would infer extraneous class constraints with variables that don't appear in the function type! eg (Num a, Ord a) => PArg -> Doc, when the correct type to infer would be PArg -> Doc. heres some gists with links to more info https://gist.github.com/3365312 https://gist.github.com/3365073 https://gist.github.com/3364775 Anyways, I'm not sure what to make of this, is this a reasonable artifact of type inference getting confused on functions with a large number of case analyses when various typeclass extensions are enabled? Or Is this a bug in terms of what inference should be able to handle? Just to be clear, when I add the infererred type ascriptions without the type class constraint, everything type checks in those modules. So my confusion is why the inference adding those unused class constraint variables! thanks all, -Carter
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