Think of porting to a new CPU architecture. If you have your compiler written in its own language, then when you add support for the new CPU target you can com

Think of porting to a new CPU architecture. If you have your compiler written in its own language, then when you add support for the new CPU target you can compiler your compiler using your compiler and target the new CPU. Now you have a compiler that not only produces code for the new CPU, but you have one that also runs on that CPU. The alternative would be to port your Haskell compiler to the new CPU too in order to set up a self hosting toolchain. Much more work involved, because you not only have to be proficient in Haskell, but you need to have Haskell compiler implementation skills in addition to your own compiler.