fix typo, stream-empty? -> set-empty? (#2191)

* fix typo, stream-empty? -> set-empty?

* add a regression test for the set->stream fallback

pkgs/racket-test-extra/tests/racket/set-regression.rkt

@@ -0,0 +1,28 @@
+#lang racket/base
+
+(require racket/generic racket/set racket/stream rackunit)
+
+(define-syntax-rule (delegate method params input wrap-output)
+  (begin
+    (define/generic generic-method method)
+    (define (method . params) (wrap-output (generic-method . input)))))
+
+(struct mask (s)
+  #:methods gen:set
+  [(delegate set-empty?  [m]   [(mask-s m)]   values)
+   (delegate set-member? [m v] [(mask-s m) v] values)
+   (delegate set-add     [m v] [(mask-s m) v] mask)
+   (delegate set-remove  [m v] [(mask-s m) v] mask)
+   (delegate set-first   [m]   [(mask-s m)]   values)
+   (delegate set-rest    [m]   [(mask-s m)]   mask)])
+
+;; ---
+
+(check set=?
+       (list 3 5 8)
+       (stream->list (set->stream (mask (set 3 5 8)))))
+
+(check set=?
+       (list 2 4 8)
+       (set->list (mask (set 2 4 8))))
+

racket/collects/racket/private/set.rkt

@@ -125,13 +125,13 @@
     [(set-implements? s 'set-empty? 'set-first 'set-rest)
      (let loop ([s s])
        (cond
-         [(stream-empty? s) empty-stream]
+         [(set-empty? s) empty-stream]
          [else (stream-cons (set-first s)
                             (loop (set-rest s)))]))]
     [(set-implements? s 'set-empty? 'set-first 'set-remove)
      (let loop ([s s])
        (cond
-         [(stream-empty? s) empty-stream]
+         [(set-empty? s) empty-stream]
          [else (stream-cons (set-first s)
                             (loop (set-remove s (set-first s))))]))]
     [(set-implements? s 'set-count 'set-first 'set-rest)