ghc-3.02-i386-unknown-bin... taken from
dcs.gla.ac.uk..../glasgow/3.02
runs into a bug (?) when compiling the program
--------------------------------------------------------------------
module T where
type Cp a = a -> a -> Ordering
m :: Eq a => Cp a -> [a] -> a
m _ [x,y,z] = if x==y then x else z
cpPairs :: Cp [j] -> (a,[j]) -> (a,[j]) -> Ordering
cpPairs cp (_,p) (_,q) = cp p q
mp :: (Eq i,Eq j) => Cp [j] -> [(i,[j])] -> (i,[j])
mp cp dD =
let minInRow = m (cpPairs cp)
in minInRow dD
-- m (cpPairs cp) dD
------------------------------------------------------------------
ghc -c -v T.hs
gives
The Glorious Glasgow Haskell Compilation System, version 3.02,
patchlevel 0
Effective command line: -c -v
Ineffective C pre-processor:
echo '{-# LINE 1 "T.hs" -}' > /tmp/ghc582.cpp && cat T.hs >>
/tmp/ghc582.cpp
real 0m0.001s
user 0m0.000s
sys 0m0.000s
ghc:recompile:Input file T.hs newer than T.o
Haskell compiler:
/usr/ghc/3.02/lib/ghc-3.02/hsc ,-W ,/tmp/ghc582.cpp
-fignore-interface-pragmas -fomit-interface-pragmas -fsimplify
[ -ffloat-lets-exposing-whnf -ffloat-primops-ok -fcase-of-case
-fdo-case-elim -freuse-con -fpedantic-bottoms -fmax-simplifier-iterations4 ]
-fwarn-overlapping-patterns -fwarn-missing-methods -fwarn-duplicate-exports
-himap=.%.hi:/usr/ghc/3.02/lib/ghc-3.02/imports/std%.hi -v
-hifile=/tmp/ghc582.hi -C=/tmp/ghc582.hc +RTS -H6000000 -K1000000
Glasgow Haskell Compiler, version 3.02, for Haskell 1.4
T.hs:24:
Ambiguous type variable(s)
`j' in the constraint `Eq (aYD, [j])'
arising from use of `m' at T.hs:24
In an equation for function `mp':
mp cp dD = let minInRow = m (cpPairs cp) in minInRow dD
T.hs:24:
Ambiguous type variable(s)
`j' in the constraint `Eq (aYD, [j])'
arising from use of `m' at T.hs:24
In an equation for function `mp':
mp cp dD = let minInRow = m (cpPairs cp) in minInRow dD
Compilation had errors
real 0m1.550s
user 0m1.480s
sys 0m0.070s
deleting... /tmp/ghc582.cpp /tmp/ghc582.hi /tmp/ghc582.hc
rm -f /tmp/ghc582*
------------------------------------------------------------------
A slight change mp ... = m (cpPairs cp) dD improves it.
Also, very probably, ghc-3.01 is free of this bug.
Sadly, i cannot guess so far what to change in my real program,
because there the things are more complex.
Please, advise.
------------------
Sergey Mechveliani
[EMAIL PROTECTED]
