#2334: panic using type families and type classes
---------------------------+------------------------------------------------
Reporter: pgavin | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.9
Severity: normal | Resolution:
Keywords: type families | Difficulty: Unknown
Testcase: | Architecture: x86
Os: MacOS X |
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Comment (by simonmar):
The following smaller example elicits the "Data.List.head: empty list"
panic:
{{{
{-# LANGUAGE TypeFamilies,EmptyDataDecls,MultiParamTypeClasses #-}
module Test where
data family F r
newtype instance F () = F deriving Eq
}}}
and it seems to happen during Renamer/Typechecker. Removing "deriving
(Eq)" makes the error go away.
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2334#comment:2>
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