One great thing about sbcl is you can put (declare (optimize (speed 3))) at the top of a function and the compiler will give useful feedback when it can’t optim

One great thing about sbcl is you can put (declare (optimize (speed 3))) at the top of a function and the compiler will give useful feedback when it can’t optimize something and suggest type hints to improve performance. I’m not a optimization wizard, but I’ve been able to get some very impressive speed ups this way, in combination with some attention to how my code is written.