In addition to argv[0]

http://hackage.haskell.org/packages/archive/system-argv0/0.1/doc/html/System-Argv0.html

There is also this package:

http://hackage.haskell.org/packages/archive/FindBin/0.0.5/doc/html/System-Environment-FindBin.html

System-Argv0 has special cases for windows- FindBin may not work there.