Added apply-if-exists

darcs-hash:20080526151359-3cc5d-643a522cb11ca8928d27fc9c7c0f8d620fbb4c81.gz

dev/l0-utils.lisp

@@ -247,9 +247,15 @@ not sticky."
    ((ensure (not (dotted-pair-p '(a b . c)))))
    ((ensure (not (dotted-pair-p nil))))))
 
-
-
-
-
-
-
+(defun apply-if-exists (function package &rest args)
+  "If the function `function` can be found in `package`, then call it 
+with `args`.
+
+Returns nil if `package` does not exist or if `function` does not name a 
+function in `package`. Otherwise, returns whatever `function` returns."
+  (let ((package (find-package package)))
+    (when package
+      (let ((symbol (find-symbol function package)))
+	(when (and symbol (fboundp symbol))
+	  (apply symbol args))))))
+

dev/package.lisp

@@ -35,6 +35,9 @@
 
                 #:without-interrupts)
 
+  (:export
+   #:apply-if-exists)
+
   (:export
    #:defclass-property
    #:deprecated