1 files changed, 17 insertions, 0 deletions
diff --git a/lazybones.lisp b/lazybones.lisp
index 2b28be7..5ccbf6f 100644
--- a/lazybones.lisp
+++ b/lazybones.lisp
@@ -379,6 +379,23 @@ of each NAME, or NIL if there is no such parameter."
                   collect `(,name (cdr (assoc ,string-name ,params :test #'string-equal))))
         ,@body))))
 
+(defmacro map-parameters ((&rest params) &body body)
+  "PARAMS is a list of pairs (NAME PARSER).  MAP-PARAMETERS behaves
+exactly like LET-PARAMETERS except that the values boudn to NAMEs are
+first mapped with the PARSER function."
+  (assert (loop for (name parser) in params
+                always (and (symbolp name)
+                            (or (symbolp parser) (functionp parser))))
+          ()
+          "Malformed PARAMS in MAP-PARAMETERS macro")
+
+  (let ((names (mapcar #'car params)))
+    `(let-parameters ,names
+       (let ,(loop for name in names
+                   collect `(,name (when ,name (funcall ',(second (assoc name params)) ,name))))
+         ,@body))))
+
+
 (defun http-ok (content)
   "Content should be a string, a byte-vector, or a pathname to a local
 file.  CONTENT-TYPE should be a MIME type string."