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Panic on a context with additional variable

    • Closed Issue created by Krzysztof Gogolewski @monoidal

    File:

    {-# LANGUAGE GADTs #-}
data X a where
  N :: (a ~ b) => X a

k :: X a -> X b
k N = N

    Result with HEAD:

    X.hs:6:7:
    Couldn't match type ‛b’ with ‛b1’
      ‛b’ is untouchable
        inside the constraints (a ~ b)
        bound by a pattern with constructor
                   N :: forall a. a ~ b => X a,
                 in an equation for ‛k’
        at X.hs:6:3ghc: panic! (the 'impossible' happened)
  (GHC version 7.7.20130608 for x86_64-unknown-linux):
	No skolem info: b{tv ae1} [sk]

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

    I got it by attempting to compile data-category with HEAD.

    Trac metadata
    Trac field Value
    Version 7.7
    Type Bug
    TypeOfFailure OtherFailure
    Priority normal
    Resolution Unresolved
    Component Compiler
    Test case
    Differential revisions
    BlockedBy
    Related
    Blocking
    CC
    Operating system
    Architecture
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