DEV Community

Vee Satayamas
Vee Satayamas

Posted on

Compile-time type checking in Common Lisp: a small experiment

#commonlisp #type

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))
Enter fullscreen mode Exit fullscreen mode

Then I ran this command:

sbcl --noinform --eval '(compile-file "static1.lisp")' --quit
Enter fullscreen mode Exit fullscreen mode

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"
Enter fullscreen mode Exit fullscreen mode

So SBCL - a Common Lisp implementation, can check type in compile-time. Anyway, a programmer needs to read warnings.

Top comments (0)