OK, I'm trying to get a more-recent GHC working that has that #ifdef that you mentioned. Specifically, 6.10.4. I've said: ./configure --build=x86_64-apple-darwin --host=x86_64-apple-darwin -- target=x86_64-apple-darwin --with-gmp-includes='/sw/include' --with- gmp-libraries='/sw/lib' make and it fails, saying it can't find libgmp, even though I've just told it where gmp is. I've copied my mk/build.mk straight from my 6.8.3 build, and it says ReadlineIncludePath=/sw/include SRC_CC_OPTS += -I/sw/include -L/sw/lib SRC_HC_OPTS += -I/sw/include -L/sw/lib EXTRA_HSC2HS_OPTS += -I/sw/include EXTRA_LD_OPTS += -L/sw/lib The resulting error message is: [51 of 51] Compiling Distribution.Simple ( Distribution/Simple.hs, dist-bootstrapping/build/Distribution/Simple.o ) ar: creating archive dist-bootstrapping/build/libHSCabal-1.6.0.3.a cd Cabal && /Users/bjs/Desktop/GHC_Build/ghc-6.10.4/libraries/cabal- bin /Users/bjs/Desktop/GHC_Build/install/bin/ghc /Users/bjs/Desktop/ GHC_Build/ghc-6.10.4/libraries/bootstrapping.conf 1.6.0.3 install -- distpref=dist-bootstrapping --inplace Installing library in /Users/bjs/Desktop/GHC_Build/ghc-6.10.4/libraries/Cabal/dist- bootstrapping/install/usr/local/lib/Cabal-1.6.0.3/ghc-6.8.3 Registering Cabal-1.6.0.3... Reading package info from "dist-bootstrapping/inplace-pkg-config" ... done. Saving old package config file... done. Writing new package config file... done. cd hpc && /Users/bjs/Desktop/GHC_Build/ghc-6.10.4/libraries/cabal- bin /Users/bjs/Desktop/GHC_Build/install/bin/ghc /Users/bjs/Desktop/ GHC_Build/ghc-6.10.4/libraries/bootstrapping.conf 1.6.0.3 clean -- distpref=dist-bootstrapping cleaning... cd hpc && /Users/bjs/Desktop/GHC_Build/ghc-6.10.4/libraries/cabal- bin /Users/bjs/Desktop/GHC_Build/install/bin/ghc /Users/bjs/Desktop/ GHC_Build/ghc-6.10.4/libraries/bootstrapping.conf 1.6.0.3 configure -- distpref=dist-bootstrapping --with-compiler=/Users/bjs/Desktop/ GHC_Build/install/bin/ghc --with-hc-pkg=/Users/bjs/Desktop/GHC_Build/ install/bin/ghc-pkg --package-db=/Users/bjs/Desktop/GHC_Build/ ghc-6.10.4/libraries/bootstrapping.conf.tmp Configuring hpc-0.5.0.3... <command-line>: warning: "__PIC__" redefined <built-in>: warning: this is the location of the previous definition cd hpc && /Users/bjs/Desktop/GHC_Build/ghc-6.10.4/libraries/cabal- bin /Users/bjs/Desktop/GHC_Build/install/bin/ghc /Users/bjs/Desktop/ GHC_Build/ghc-6.10.4/libraries/bootstrapping.conf 1.6.0.3 build -- distpref=dist-bootstrapping Preprocessing library hpc-0.5.0.3... ld: library not found for -lgmp collect2: ld returned 1 exit status linking dist-bootstrapping/build/Trace/Hpc/Reflect_hsc_make.o failed command was: /usr/bin/gcc -L/Users/bjs/Desktop/GHC_Build/install/lib/ ghc-6.8.3/lib/directory-1.0.0.1 -L/Users/bjs/Desktop/GHC_Build/install/ lib/ghc-6.8.3/lib/filepath-1.1.0.0 -L/Users/bjs/Desktop/GHC_Build/ install/lib/ghc-6.8.3/lib/old-time-1.0.0.0 -L/Users/bjs/Desktop/ GHC_Build/install/lib/ghc-6.8.3/lib/old-locale-1.0.0.0 -L/Users/bjs/ Desktop/GHC_Build/install/lib/ghc-6.8.3/lib/containers-0.1.0.2 -L/ Users/bjs/Desktop/GHC_Build/install/lib/ghc-6.8.3/lib/array-0.1.0.0 -L/ Users/bjs/Desktop/GHC_Build/install/lib/ghc-6.8.3/lib/base-3.0.2.0 -L/ Users/bjs/Desktop/GHC_Build/install/lib/ghc-6.8.3 -lm -lgmp -ldl dist- bootstrapping/build/Trace/Hpc/Reflect_hsc_make.o -o dist-bootstrapping/ build/Trace/Hpc/Reflect_hsc_make make[1]: *** [bootstrapping.conf] Error 1 make: *** [stage1] Error 2 [~/Desktop/GHC_Build/ghc-6.10.4] bjs$ As you can see, it doesn't even attempt to tell gcc where to find libgmp. This has the feeling of an RTM question, and if it is then I apologise. I've not seen anything about this in the M, though. Cheers, Barney.