Add MAP and FLAT-MAP functions

lisp/lang/functions.lisp

@@ -10,6 +10,33 @@
    (t (cons (funcall function-name the-list)
        (maplist function-name (rest the-list))))))
 
+(defun map (function the-list)
+  (reverse (map-tail function the-list nil)))
+
+(defun map-tail (function the-list accumulator)
+  (if the-list
+    (recur
+      function
+      (rest the-list)
+      (cons (call function (first the-list)) accumulator))
+    accumulator))
+
+(defun flat-map (function the-list)
+  (reverse (flat-map-tail function the-list nil)))
+
+(defun flat-map-tail (function the-list accumulator)
+  (if the-list
+    (recur
+      function
+      (rest the-list)
+      (append
+        (let ((result (call function (first the-list))))
+          (if (list? result)
+            (reverse result)
+            (list result)))
+        accumulator))
+    accumulator))
+
 (defun append (list-one list-two)
   (append-tail (reverse list-one) list-two))