Incorrect Outputable instance for InstDecl

The pretty-printer produces trash output for instance declarations. This is how the Outputable instance is defined in compiler/hsSyn/HsDecls.lhs:

instance (OutputableBndr name) => Outputable (InstDecl name) where

    ppr (InstDecl inst_ty binds uprags ats)
      = vcat [hsep [ptext SLIT("instance"), ppr inst_ty, ptext SLIT("where")],
              nest 4 (ppr ats),
              nest 4 (ppr uprags),
              nest 4 (pprLHsBinds binds) ]

Notice that 'ats' and 'uprags' are lists, so they are being printed as such, i.e., with braces and commas. This produces output that looks like this:

instance Monad Maybe where
    []
    []
    return = Just
    fail _ = Nothing
    ...

The correct (I think) definition is this:

instance (OutputableBndr name) => Outputable (InstDecl name) where
    ppr (InstDecl inst_ty binds uprags ats)
      = vcat ([hsep [ptext SLIT("instance"), ppr inst_ty, ptext SLIT("where")]] ++
	      [ nest 4 (ppr at) | at <- ats ] ++ 
	      [ nest 4 (ppr uprag) | uprag <- uprags ] ++ 
	      [ nest 4 (pprLHsBinds binds) ])

Trac metadata

Trac field	Value
Version	6.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	df@dfranke.us
Operating system	Multiple
Architecture	Multiple