implicit parameters and type synonyms

I wouldn't call this a bug. But we have various pieces of code at Galois that rely on this undocumented (AFAIK) feature of GHC:

Allow implicit parameter constraints in type synonyms and float the constraints out when the synonym is used.

So, given the following program:

{-# OPTIONS -fglasgow-exts -fimplicit-params #-}
module TestIP where

type PPEnv = Int
type Doc   = Char
    
type PPDoc = (?env :: PPEnv) => Doc

f :: Char -> PPDoc
f = succ    

In ghc 6.4.1 and 6.2.1 it compiles fine. In ghc 6.5.20060526 I get this:

src $ ghci ~/TestIP.hs 
   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 6.5.20060526, for Haskell 98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.

Loading package base-1.0 ... linking ... done.
[1 of 1] Compiling TestIP           ( /Users/tullsen/TestIP.hs, interpreted )

/Users/tullsen/TestIP.hs:10:4:
    Couldn't match expected type `PPDoc' against inferred type `Char'
    Probable cause: `succ' is applied to too many arguments
    In the expression: succ
    In the definition of `f': f = succ
Failed, modules loaded: none.
Prelude> 

So, my question is Is this a bug or the removing of an undocumented 'feature'?

Thanks,

Mark

Trac metadata

Trac field	Value
Version	6.5
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
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Blocking
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Operating system	Unknown
Architecture	Unknown