Comment by sehugg

I've implemented Atari 2600 library support for both LLVM-MOS and CC65, but there are too many compromises to make it suitable for writing a game.

The lack of RAM is a major factor; stack usage must be kept to a minimum and you can forget any kind of heap. RAM can be extended with a special mapper, but due to the lack of a R/W pin on the cartridge, reads and writes use different address ranges, and C does not handle this without a hacky macro solution.

Not to mention the timing constraints with 2600 display kernels and page-crossing limitations, bank switching, inefficient pointer chasing, etc. etc. My intuition is you'd need a SMT solver to write a language that compiles for this system without needing inline assembly.