Ported helpers.rkt to #lang whalesong

whalesong/selfhost/helpers.rkt

@@ -0,0 +1,58 @@
+#lang whalesong (require "selfhost-lang.rkt") (require whalesong/lang/for)
+; #lang typed/racket/base
+(require racket/list)
+(provide list-union list-difference list-intersection unique/eq? unique/equal?)
+
+
+(: list-union ((Listof Symbol) (Listof Symbol) -> (Listof Symbol)))
+(define (list-union s1 s2)
+  (cond [(null? s1) s2]
+        [(memq (car s1) s2)
+         (list-union (cdr s1) s2)]
+        [else (cons (car s1) (list-union (cdr s1) s2))]))
+
+
+(: list-difference ((Listof Symbol) (Listof Symbol) -> (Listof Symbol)))
+(define (list-difference s1 s2)
+  (cond [(null? s1) '()]
+        [(memq (car s1) s2)
+         (list-difference (cdr s1) s2)]
+        [else
+         (cons (car s1) (list-difference (cdr s1) s2))]))
+
+(: list-intersection ((Listof Symbol) (Listof Symbol) -> (Listof Symbol)))
+(define (list-intersection s1 s2)
+  (cond [(null? s1) '()]
+        [(memq (car s1) s2)
+         (cons (car s1) (list-intersection (cdr s1) s2))]
+        [else
+         (list-intersection (cdr s1) s2)]))
+
+
+;; Trying to work around what looks like a bug in typed racket:
+(define string-sort (inst sort String String))
+
+(: unique/eq? ((Listof Symbol) -> (Listof Symbol)))
+(define (unique/eq? los)
+  (let ([ht ; : (HashTable Symbol Boolean) 
+            (make-hasheq)])
+    (for ([l los])
+      (hash-set! ht l #t))
+    (map string->symbol
+         (string-sort
+          (hash-map ht (lambda (k v) ;  ([k : Symbol] [v : Boolean]) 
+                                (symbol->string k)))
+          string<?))))
+
+
+
+(: unique/equal? (All (A) ((Listof A) -> (Listof A))))
+(define (unique/equal? lst)
+  (cond
+    [(empty? lst)
+     empty]
+    [(member (first lst) (rest lst))
+     (unique/equal? (rest lst))]
+    [else
+     (cons (first lst)
+           (unique/equal? (rest lst)))]))