(For advice about overly slow or memory-hungry Haskell programs, please see Chapter 7, Advice on: sooner, faster, smaller, thriftier).
If your program has no foreign calls in it, and no
calls to known-unsafe functions (such as
unsafePerformIO) then a crash is always a
BUG in the GHC system, except in one case: If your program
is made of several modules, each module must have been
compiled after any modules on which it depends (unless you
.hi-boot files, in which case these
must be correct with respect to the
For example, if an interface is lying about the type of an imported value then GHC may well generate duff code for the importing module. This applies to pragmas inside interfaces too! If the pragma is lying (e.g., about the “arity” of a value), then duff code may result. Furthermore, arities may change even if types do not.
In short, if you compile a module and its interface changes, then all the modules that import that interface must be re-compiled.
If you are using make, GHC can automatically generate the dependencies required in order to make sure that every module is up-to-date with respect to its imported interfaces. Please see Section 5.6.11, “Dependency generation”.
If you are down to your
last-compile-before-a-bug-report, we would recommend that
you add a
-dcore-lint option (for extra
checking) to your compilation options.
So, before you report a bug because of a core dump, you should probably:
% rm *.o # scrub your object files % make my_prog # re-make your program; use -hi-diffs to highlight changes; # as mentioned above, use -dcore-lint to be more paranoid % ./my_prog ... # retry...
Of course, if you have foreign calls in your program then all bets are off, because you can trash the heap, the stack, or whatever.
This is definitely caused by a bug in GHC. Please report it (see Section 1.2, “Reporting bugs in GHC”).
Double arithmetic is
unchecked. Overflows, underflows and
loss of precision are either silent or reported as an
exception by the operating system (depending on the
platform). Divide-by-zero may cause an
untrapped exception (please report it if it does).