Maybe BBEdit, if it is still a free download, Peter and Gale know more about it than I do. Also, I am working on CodeWarrior integration (which has in my humble opinion the friendliest text editor (I have been working with it for over ten years now, day and night)). You can also try Apple's ProjectBuilder, which is included with the above ADC downloads.
BBEdit is good, but no longer free (& hasn't been for a while). Its now $US179. There is a demo, but this run for 'x' number of days... (I forget what x is!)
I have good memories of the CodeWarrior editor too, but you pay for that too, but at least they have (had?!) a student version.
You can of course edit in ProjectBuilder (comes free on the developer's CD), but I think that all you can do with GPC and ProjectBuilder thus far... kind-of a heavy-weight solution and I feel BBEdit is the better editor. I does seem to "know" Pascal syntax either (either that, or its generic guesses are good enough).
Grant