adding implementation of sets

sets.rkt

@@ -0,0 +1,40 @@
+#lang typed/racket/base
+
+(define-struct: (A) set ([ht : (HashTable A Boolean)]))
+(define-type (Setof A) (set A))
+
+(: new-set (All (A) (->  (Setof A))))
+(define (new-set)
+  (make-set ((inst make-hash A Boolean))))
+
+(: new-seteq (All (A) (->  (Setof A))))
+(define (new-seteq)
+  (make-set ((inst make-hasheq A Boolean))))
+
+(: set-insert! (All (A) ((Setof A) A -> Void)))
+(define (set-insert! s elt)
+  (hash-set! (set-ht s) elt #t)
+  (void))
+  
+(: set-remove! (All (A) ((Setof A) A -> Void)))
+(define (set-remove! s elt)
+  ((inst hash-remove! A Boolean) (set-ht s) elt)
+  (void))
+
+(: set-contains? (All (A) ((Setof A) A -> Boolean)))
+(define (set-contains? s elt)
+  (hash-has-key? (set-ht s) elt))
+
+(: set-for-each (All (A) ((A -> Any) (Setof A) -> Void)))
+(define (set-for-each f s)
+  ((inst hash-for-each A Boolean Any)
+   (set-ht s)
+   (lambda: ([k : A] [v : Boolean])
+            (f k)))
+  (void))
+
+
+(: set-map (All (A B) ((A -> B) (Setof A) -> (Listof B))))
+(define (set-map f s)
+  ((inst hash-map A Boolean B) (set-ht s) (lambda: ([k : A] [v : Boolean])
+                                                   (f k))))