SBCL (the implementation) gives us pretty useful type errors and warnings. It is not "fully typed" (see Coalton for a Haskell-in-Lisp) but very useful anyways:

SBCL (the implementation) gives us pretty useful type errors and warnings. It is not "fully typed" (see Coalton for a Haskell-in-Lisp) but very useful anyways: it warns on a function arguments not having the right types, stuff like this. The nice part is that we get these warnings instantly, since we compile the code function by function. We can add type declarations, that help the compiler further infer types, throw more warnings, and optimize code.