id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
3823,GHC 6.12 breaks combination of records and mutually recursive modules,mboes,igloo,"Take the following code for two mutually recursive modules A and B:
{{{
module A where

import B

data A = X { x :: Bool } | Y

y :: A -> A
y = \_ -> Y

-- A.hs-boot
module A where

data A = X { x :: Bool } | Y

y :: A -> A

module B where

import {-# SOURCE #-} A

data B = A A

a = x (X True)
b = y a
}}}
Compiling this code with ghc --make or ghci gives:
{{{
[1 of 3] Compiling A[boot]          ( A.hs-boot, A.o-boot )
[2 of 3] Compiling B                ( B.hs, B.o )

B.hs:7:4:
    Can't find interface-file declaration for variable x
      Probable cause: bug in .hi-boot file, or inconsistent .hi file
      Use -ddump-if-trace to get an idea of which file caused the error
    In the expression: x (X True)
    In the definition of `a': a = x (X True)
}}}
This code used to work in GHC 6.10.

Note that this issue breaks the build of the hmk package on Hackage. Doubtless other packages making use of mutually recursive modules hit this snag too.",merge,closed,high,6.12.2,Compiler,6.12.1,fixed,,,Unknown/Multiple,Unknown/Multiple,GHC rejects valid program,,T3823,,,