The runghc commandline looks like:

runghc [runghc flags] [GHC flags] module [program args]

The only runghc flag currently is -f /path/to/ghc, which tells runghc which GHC to use to run the program. If it is not given then runghc will search for GHC in the directories in the system search path.

runghc will try to work out where the boundaries between [runghc flags] and [GHC flags], and [GHC flags] and module are, but you can use a -- flag if it doesn't get it right. For example, runghc -- -fglasgow-exts Foo means runghc won't try to use glasgow-exts as the path to GHC, but instead will pass the flag to GHC. If a GHC flag doesn't start with a dash then you need to prefix it with --ghc-arg= or runghc will think that it is the program to run, e.g. runghc -package-conf --ghc-arg=foo.conf Main.hs.