I'm on Mac OS 10.4.2, using ghc 6.4 (from the haskell.org .dmg) and gcc 4.0.0. Other wxHaskell programs (the samples and my own experiments) compile without tripping over this.
GHC 6.4 is incompatible with gcc 4.0.0 when -O or -via-C is used. You can work around this problem by either not using -via-C and always adding -fasm *after* -O, or by setting your default compiler to gcc-3.3 using sudo gcc_select 3.3 ... but be aware that this also affects other C compilations; switch back using sudo gcc_select 4.0 I suspect that you compiled the program with -O before, and then switched to -O0 without removing your .o files. If you compiled wxHaskell yourself, then the problem might also be in wxHaskell (you'd have to recompile it then). The upcoming GHC 6.4.1 will of course fix this problem. Cheers, Wolfgang