for ,new = (cdr ,old)
until (eq ,old (setf ,old ,cas-form))
finally (return (car ,old))))))
+
+(defun split-version-string (string)
+ (loop with subversion and start = 0
+ with end = (length string)
+ when (setf (values subversion start)
+ (parse-integer string :start start :junk-allowed t))
+ collect it
+ while (and subversion
+ (< start end)
+ (char= (char string start) #\.))
+ do (incf start)))
+
+(defun version>= (x y)
+ (unless (or x y)
+ (return-from version>= t))
+ (let ((head-x (or (first x) 0))
+ (head-y (or (first y) 0)))
+ (or (> head-x head-y)
+ (and (= head-x head-y)
+ (version>= (rest x) (rest y))))))
+
+(defun assert-version->= (&rest subversions)
+ #!+sb-doc
+ "Asserts that the current SBCL is of version equal to or greater than
+the version specified in the arguments. A continuable error is signaled
+otherwise.
+
+The arguments specify a sequence of subversion numbers in big endian order.
+They are compared lexicographically with the runtime version, and versions
+are treated as though trailed by an unbounded number of 0s.
+
+For example, (assert-version->= 1 1 4) asserts that the current SBCL is
+version 1.1.4[.0.0...] or greater, and (assert-version->= 1) that it is
+version 1[.0.0...] or greater."
+ (let ((version (split-version-string (lisp-implementation-version))))
+ (unless (version>= version subversions)
+ (cerror "Disregard this version requirement."
+ "SBCL ~A is too old for this program (version ~{~A~^.~} ~
+ or later is required)."
+ (lisp-implementation-version)
+ subversions))))