class instance lost during re-export & packaging

The package TV defines an instance OFun (in module Interface.TV.OFun, source here) for a type class FunArr in the package DeepArrow. The module Interface.TV (source here) re-exports Interface.TV.OFun in its entirety.

When I compile a test program that imports Interface.TV, under ghc-6.6, the OFun instance of !FunArr is not found. If the test module also says "import Interface.TV.OFun()", the instance is found. I get this behavior with ghc, ghc --make, and ghci.

The test program:

module Bug where

import Interface.TV.UI

-- Required to pick up the FunArr instance for OFun.  GHC bug?
import Interface.TV.OFun()

reverseT :: TV KIO (String -> String)
reverseT = tv (oTitle "reverse" defaultOut) reverse

revTwice :: TV KIO (String -> String)
revTwice = reverseT ->| reverseT

Test compile:

bash-3.2$ ghc -c Bug.hs
bash-3.2$ 

If I comment out the second import line, the problem surfaces:

ghc -c Bug.hs

Bug.hs:12:11:
    No instance for (FunArr ar (Output KIO))
      arising from use of `->|' at Bug.hs:12:11-31
    Possible fix:
      add an instance declaration for (FunArr ar (Output KIO))
    In the expression: reverseT ->| reverseT
    In the definition of `revTwice': revTwice = reverseT ->| reverseT
bash-3.2$ 

More details:

bash-3.2$ uname -a
CYGWIN_NT-5.1 Compy 1.5.24(0.156/4/2) 2007-01-31 10:57 i686 Cygwin

bash-3.2$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.6

bash-3.2$ ghc -v -c Bug.hs
Glasgow Haskell Compiler, Version 6.6, for Haskell 98, compiled by GHC version 6.6
Using package config file: c:\ghc\ghc-6.6\package.conf
wired-in package base mapped to base-2.0
wired-in package rts mapped to rts-1.0
wired-in package haskell98 mapped to haskell98-1.0
wired-in package template-haskell mapped to template-haskell-2.0
Hsc static flags: -static
Created temporary directory: c:/tmp/ghc3880_0
*** Checking old interface for main:Bug:
*** Parser:
*** Renamer/typechecker:

Bug.hs:12:11:
    No instance for (FunArr ar (Output KIO))
      arising from use of `->|' at Bug.hs:12:11-31
    Possible fix:
      add an instance declaration for (FunArr ar (Output KIO))
    In the expression: reverseT ->| reverseT
    In the definition of `revTwice': revTwice = reverseT ->| reverseT
*** Deleting temp files:
Deleting: c:/tmp/ghc3880_0/ghc3880_0.s
Warning: deleting non-existent c:/tmp/ghc3880_0/ghc3880_0.s
*** Deleting temp dirs:
Deleting: c:/tmp/ghc3880_0
bash-3.2$ 

Trac metadata

Trac field	Value
Version	6.6
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown