[plt-scheme] (no subject)

I'm having a slight problem with mzc on my Mac OS X.  This is the  
order of what I did:
mzc -c first_scheme.scm
mzc --cc first_scheme.c
gcc first_scheme.o -o first_scheme -framework PLT_MzScheme
That last command gives me this error:
/usr/bin/ld: Undefined symbols:
_main
collect2: ld returned 1 exit status
So I looked through the code and sure enough there is no main  
function.  How is it supposed to compile?  Am I missing something here?