In static1.lisp:
(defpackage static1
(:use #:cl))
(in-package :static1)
(declaim (ftype (function (string string) string) concat-strings))
(defun concat-strings (a b)
(format nil "~A --- ~A" a b))
(declaim (ftype (function (fixnum fixnum) string) concat-nums))
(defun concat-nums (a b)
(concat-strings a b))
Then I ran this command:
sbcl --noinform --eval '(compile-file "static1.lisp")' --quit
SBCL showed this warning:
; caught WARNING:
; Derived type of STATIC1::A is
; (VALUES FIXNUM &OPTIONAL),
; conflicting with its asserted type
; STRING.
; See also:
; The SBCL Manual, Node "Handling of Types"
So SBCL - a Common Lisp implementation, can check type in compile-time. Anyway, a programmer needs to read warnings.
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