I never had to use the compiler back in my early Mac programming days, as I got into Mac programming starting with Lightspeed C (later THINK C). Some of my friends used MPW, though. MPW was much more expensive. I do remember having to use it years later when I was trying to compile an C library for use on the Newton. I discovered that it was pretty far from an ANSI/ISO compliant C - for example, it didn't accept the question mark (ternary) operator at all. But the MPW toolset was very cool, including the Worksheet concept. I still use the Worksheet concept in BBEdit on MacOS X and it is wonderful; I use it to handle the workflow for producing podcast episodes.