That's where a dynamically typed language with optional typing gets handy, when a compiler supports it... In Common Lisp, the SBCL compiler would be such an e

That's where a dynamically typed language with optional typing gets handy, when a compiler supports it... In Common Lisp, the SBCL compiler would be such an example: * (defun foo () (let ((i 10) (s "20")) (concatenate 'string s i))) ; in: DEFUN FOO ; (CONCATENATE 'STRING S I) ; ; caught WARNING: ; Derived type of I is ; (VALUES (INTEGER 10 10) &OPTIONAL), ; conflicting with its asserted type ; SEQUENCE. ; See also: ; The SBCL Manual, Node "Handling of Types" ; ; compilation unit finished ; caught 1 WARNING condition FOO *