The attached tgz archive contains 4 files:
A.hs defines a type X and a type class Y
B.hs imports A and makes X an instance of Y
C.hs imports B and just exports everything again
D.hs imports C and tries to use the fact that X is an instance of Y.
If you compile this using
ghc -c [A/B/C/D].hs
then it should all go swimmingly (by the way, we are on Sparc-Solaris and using a
version
downloaded at the end of last week).
If however you compile it using
ghc -c [A/B/C/D].hs -i$PWD
(replace $PWD by the absolute path of directory containing A,B,C,D, if your shell
doesn't)
then it doesn't work. The reason is that C.hi now only contains the following:
__interface C 1 404 where
__export A X{FOO BAR} Y{p};
where it previously contained
__interface C 1 404 where
__export A X{FOO BAR} Y{p};
import A 1 ::;
import B 1 ! ::;
In other words it looks as if, because A and B were obtained from an absolute path,
ghc has decided to forget to add them to C's import list, so that the instance
declaration
in B gets lost.
This is really exceptionally confusing. I am not sure if it is intended or not, but I
certainly don't like it, and it doesn't seem to be documented. If the use of
absolute path names for interface files is deprecated then ITWSBT!
bug.tar.gz
