#3423: (Standalone deriving + tyfamilies + recursive instance cxt +
UndecidableInstances + ghc >= 6.10.2) No match in record selector
Var.tcTyVarDetails
-----------------------------+----------------------------------------------
Reporter: morrow | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.10.4 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
-----------------------------+----------------------------------------------
This seems to have been introduced in 6.10.2:
{{{
{-# OPTIONS_GHC -fglasgow-exts #-}
{-# LANGUAGE UndecidableInstances #-}
module Bug where
newtype Trie m k a = Trie (Maybe a, m (SubKey k) (Trie m k a))
type family SubKey k
type instance SubKey [k] = k
deriving instance (Eq (m k (Trie m [k] a))
,Eq a) => Eq (Trie m [k] a)
}}}
which fails with:
{{{
[...@monire ~]$ ghc -O2 -c --make Bug.hs
[1 of 1] Compiling Bug ( Bug.hs, Bug.o )
ghc: panic! (the 'impossible' happened)
(GHC version 6.10.3 for x86_64-unknown-linux):
No match in record selector Var.tcTyVarDetails
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
}}}
Matt
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3423>
GHC <http://www.haskell.org/ghc/>
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