id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
2775,Type Family panic,camio,chak,"The following code produces the ghc panic below.
{{{
{-# LANGUAGE RankNTypes, TypeFamilies #-}
import Data.VectorSpace 

data I  = I { integral :: (VectorSpace v, Scalar v ~ Double) => v
            }

-- This works
-- integral :: (VectorSpace v, Scalar v ~ Double) => v
-- integral = undefined

-- type BallAnim = Input -> Behavior Ball

followMouse i = integral undefined undefined
}}}

{{{
ff>ghci GhcBug.hs
GHCi, version 6.10.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main             ( GhcBug.hs, interpreted )
: panic! (the 'impossible' happened)
  (GHC version 6.10.1 for i386-unknown-mingw32):
        applyTypeToArgs
    ipv{v B4} [lid]
      @ (a{tv arL} [sk] -> t_arM{tv} [sk])
      $dVectorSpace{v arP} [lid]
      (base:GHC.Err.undefined{v rdH} [gid] @ a{tv arL} [sk])
    (vector-space-0.5:Data.VectorSpace.Scalar{tc rgl}
       (a{tv arL} [sk] -> t_arM{tv} [sk])
       ~
     ghc-prim:GHC.Types.Double{(w) tc 3u}) =>
    a{tv arL} [sk] -> t_arM{tv} [sk]

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
}}}",bug,closed,normal,6.12.1,Compiler,6.10.1,fixed,,ganesh,Unknown/Multiple,Unknown/Multiple,,Unknown,,,,