If you still have a problem after consulting this section,
then you may have found a bug—please
report it! See Section 1.2 for details on how to
report a bug and a list of things we'd like to know about your bug.
If in doubt, send a report—we love mail from irate users
(Section 12.1, which describes Glasgow
Haskell's shortcomings vs. the Haskell language definition, may
also be of interest.)
These events are always bugs in
the GHC system—please report them.
“This is a terrible error message.”
If you think that GHC could have produced a better
error message, please report it as a bug.
“What about this warning from the C
For example: “…warning: `Foo' declared
`static' but never defined.” Unsightly, but shouldn't
be a problem.
Sensitivity to .hi interface files:
GHC is very sensitive about interface files. For
example, if it picks up a non-standard
Prelude.hi file, pretty terrible things
will happen. If you turn on
-fno-implicit-prelude, the compiler will almost
surely die, unless you know what you are doing.
Furthermore, as sketched below, you may have big
problems running programs compiled using unstable
“I think GHC is producing incorrect code”:
Unlikely :-) A useful be-more-paranoid option to give
to GHC is
-dcore-lint; this causes a
“lint” pass to check for errors (notably type
errors) after each Core-to-Core transformation pass. We run
with -dcore-lint on all the time; it costs
about 5% in compile time.
“Why did I get a link error?”
If the linker complains about not finding
then something is inconsistent: you probably didn't compile
modules in the proper dependency order.
“Is this line number right?”
On this score, GHC usually does pretty well,
especially if you “allow” it to be off by one or
two. In the case of an instance or class declaration, the
line number may only point you to the declaration, not to a
Please report line-number errors that you find