[GHC] #5566: instance decls via TH: dropped methods and stack overflows

[GHC]

#5566: instance decls via TH: dropped methods and stack overflows
---------------------------------+------------------------------------------
    Reporter:  FSalad            |       Owner:                  
        Type:  bug               |      Status:  new             
    Priority:  normal            |   Component:  Template Haskell
     Version:  7.2.1             |    Keywords:                  
    Testcase:                    |   Blockedby:                  
          Os:  Unknown/Multiple  |    Blocking:                  
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
---------------------------------+------------------------------------------
 {{{
 {-# LANGUAGE TemplateHaskell #-}

 class C a where
     c :: a

 $([d| instance C Int where c = 0 |] )

 data D = D

 $([d| instance C D where c = D |] )

 $([d| instance Show D where show _ = "D" |] )
 }}}

 Loading this into GHCI:

 {{{
 /tmp/Foo.hs:6:3:
     Warning: No explicit method nor default method for `c'
     In the instance declaration for `C Int'

 /tmp/Foo.hs:10:3:
     Warning: No explicit method nor default method for `c'
     In the instance declaration for `C D'
 Ok, modules loaded: Main.
 ghci> c :: Int
 *** Exception: /tmp/Foo.hs:6:3-35: No instance nor default method for
 class operation Main.c

 ghci> c :: D
 *** Exception: stack overflow
 ghci> show D
 "*** Exception: stack overflow
 ghci>
 }}}

 I also tried putting C and/or D into separate modules, to no effect.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5566>
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