compiling libraries with ghc

hi, i wrote some utilities to make my coding a little easier and i put them in some libraries. then to use them i made a package conf file and added it with ghc-pkg -a. i then tried compiling them with ghc -package-name extensions -c Foo.hs but i am not sure i am compiling it right as i get linker errors of the form /usr/libexec/elf/ld: cannot find -lDirectoryAndExtensions whenever i try to compile a program that uses my libraries. i can fix this by copying all the .o files to libFoo.a files. what is the right way to compile libraries? sincerly, chris moline