Solution exercises from P01 to P07

p04.el

@@ -0,0 +1,10 @@
+;; P04 (*) Find the number of element of a list
+(defun my-length (lst)
+  (defun my-length-rec (lst res)
+    (cond
+     ((eq lst '()) res)
+     (t
+      (my-length-rec (cdr lst) (+ 1 res)))))
+  (my-length-rec lst 0))
+
+(my-length '(a b c)) ; 3