#824: overlapping instances and separate compilation
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Reporter: [EMAIL PROTECTED] | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.5
Severity: normal | Keywords:
Os: Unknown | Difficulty: Unknown
Architecture: Unknown |
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There's three issues here that all seem to revolve around overlapping
instances
and separate compilation.
1) First, a documentation issue:
It is not clear whether it makes sense to set '-fallow-overlapping-
instances'
with different values per compilation unit or this flag should be
constant
across the whole build.
2) Secondly, I see that code that once worked fine in ghc 6.4 no longer
compiles with ghc 6.5. Note these files:
Makefile:
{{{
main: Main.hs Indexed.o
ghc -o main Main.hs Indexed.o
Indexed.o : Indexed.hs
ghc -fglasgow-exts -c $< # Fails
#ghc -fglasgow-exts -fallow-overlapping-instances -c $< # Works
}}}
Main.hs:
{{{
{-# OPTIONS -fglasgow-exts -fallow-overlapping-instances #-}
module Main where
import Indexed
instance Indexed [Int] Int where
xs @@ i = xs !! fromIntegral i
f :: [Int] -> Int
f ys = ys @@ (1 :: Int)
main = print (f [5..])
}}}
Indexed.hs:
{{{
module Indexed where
import Data.List
class Indexed f a where
(@@) :: Integral i => f -> i -> a
instance Indexed [a] a where
(@@) = genericIndex
}}}
I get the following:
{{{
$ make clean; make
rm *.hi *.o
ghc -fglasgow-exts -c Indexed.hs # Fails
#ghc -fglasgow-exts -fallow-overlapping-instances -c Indexed.hs # Works
ghc -o main Main.hs Indexed.o
Main.hs:9:7:
Overlapping instances for Indexed [Int] Int
arising from use of `@@' at Main.hs:9:7-22
Matching instances:
instance Indexed [a] a -- Imported from Indexed
instance [overlap ok] Indexed [Int] Int -- Defined at Main.hs:5:0
In the expression: ys @@ (1 :: Int)
In the definition of `f': f ys = ys @@ (1 :: Int)
make: *** [main] Error 1
$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.5.20060526
}}}
Is this a bug or a 6.5 feature? If it's a feature, then is there no way
to have a single object file
that can be used in one project that uses overlapping instances and
another which doesn't?
3) Thirdly, I've noticed that --make (in ghc and implicitly in ghci) seems
broken here. The recompilation checker doesn't seem to regenerate the .hi
files when pragmas such as the following come and go in the file:
{{{
{-# OPTIONS -fallow-overlapping-instances -#}
}}}
And it appears that in 6.5 the .hi should change here.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/824>
GHC <http://www.haskell.org/ghc/>
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