Are there other editors with a GUI that are free, other than Emacs, for OS X that you can write SML codes in?
Wauv! Thanks for your help my frend she's all over! So I should say thank you very much from her! ;-)
Why don't you try Aquamacs? http://aquamacs.org/
I couldn't find any info about SML support in the common editors (Textmate, BBedit, Fraise, Kod,...) but maybe the following does the job for you