CL already has strong types, it's static typing that it lacks. Though some compilers do make use of the information present to varying degrees, they'll emit warnings typically, not errors, for things like
(+ 1 "hello") ;; SBCL should emit a warning, but will let this run and you'll get a runtime type error
If it was not strongly typed then you'd be able to do the silly things you can do in JS and Perl like:
