tasks a-s

Task/Parametric-polymorphism/Racket/parametric-polymorphism.rkt

@@ -0,0 +1,20 @@
+#lang typed/racket
+
+(define-type (Tree A) (U False (Node A)))
+
+(struct: (A) Node
+  ([val : A] [left : (Tree A)] [right : (Tree A)])
+  #:transparent)
+
+(: tree-map (All (A B) (A -> B) (Tree A) -> (Tree B)))
+(define (tree-map f tree)
+  (match tree
+    [#f #f]
+    [(Node val left right)
+     (Node (f val) (tree-map f left) (tree-map f right))]))
+
+;; unit tests
+(require typed/rackunit)
+(check-equal?
+ (tree-map add1 (Node 5 (Node 3 #f #f) #f))
+ (Node 6 (Node 4 #f #f) #f))