It seems I can't compile Rts.h as C++ on Linux. Curiously it compiles OK on Darwin. $ gcc -x c -c /usr/lib/ghc-5.04/include/Rts.h $ gcc -x c++ -c /usr/lib/ghc-5.04/include/Rts.h In file included from /usr/lib/ghc-5.04/include/Stg.h:210, from /usr/lib/ghc-5.04/include/Rts.h:20: /usr/lib/ghc-5.04/include/gmp.h:1970: declaration of C function `class ostream & operator <<(ostream &, const __mpq_struct *)' conflicts with /usr/lib/ghc-5.04/include/gmp.h:1969: previous declaration `class ostream & operator <<(ostream &, const __mpz_struct *)' here /usr/lib/ghc-5.04/include/gmp.h:1971: declaration of C function `class ostream & operator <<(ostream &, const __mpf_struct *)' conflicts with /usr/lib/ghc-5.04/include/gmp.h:1970: previous declaration `class ostream & operator <<(ostream &, const __mpq_struct *)' here /usr/lib/ghc-5.04/include/gmp.h:1973: declaration of C function `class istream & operator >>(istream &, __mpq_struct *)' conflicts with /usr/lib/ghc-5.04/include/gmp.h:1972: previous declaration `class istream & operator >>(istream &, __mpz_struct *)' here /usr/lib/ghc-5.04/include/gmp.h:1974: declaration of C function `class istream & operator >>(istream &, __mpf_struct *)' conflicts with /usr/lib/ghc-5.04/include/gmp.h:1973: previous declaration `class istream & operator >>(istream &, __mpq_struct *)' here $ gcc --version 2.95.4 $ ghc --version The Glorious Glasgow Haskell Compilation System, version 5.04 $ uname -a Linux server 2.4.18-686 #1 Sun Apr 14 11:32:47 EST 2002 i686 unknown $ -- Ashley Yakeley, Seattle WA