Unnecessary constraints in inferred type
Carter Schonwald reports: 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
- 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.
Here are 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?