Generator/Exponential: Difference between revisions

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 =={{header|Racket}}==
-Racket has (potentially infinite) sequences, which handle most use cases of generators. First-class generators are also available in a library.
 <lang racket>
 #lang racket
 (require racket/generator)
-;; a generator using Racket's sequences
+;; this is a function that returns a powers generator, not a generator
-(define (powers n)
+(define (powers m)
+  (generator ()
-  (sequence-map (λ (x) (expt x n)) (in-naturals)))
+    (for ([n (in-naturals)]) (yield (expt n m)))))
 (define squares (powers 2))
-(define cubes (powers 3))
+(define cubes   (powers 3))
+;; same here
-;; using explicit generators
-(define (filter s1 s2)
+(define (filtered g1 g2)
+  (generator ()
-  (define g1 (sequence->generator s1))
-  (define g2 (sequence->generator s2))
-  (in-generator
     (let loop ([n1 (g1)] [n2 (g2)])
       (cond [(< n1 n2) (yield n1) (loop (g1) n2)]
@@ Line 1,439: / Line 1,437: @@
             [else (loop (g1) (g2))]))))
-(define filtered (filter squares cubes))
+(for/list ([x (in-producer (filtered squares cubes) (lambda (_) #f))]
+           [i 30] #:when (>= i 20))
-(for/list ([x (sequence-tail filtered 20)]
-           [_ 10])
   x)
 </lang>