From e077b87d503969029deee6f3cd8094d567c8b438 Mon Sep 17 00:00:00 2001
From: Jon Rafkind <rafkind@racket-lang.org>
Date: Tue, 24 Aug 2010 00:11:22 -0600
Subject: [PATCH] fix PR 11123: 0-ary generator yield

---
 collects/racket/generator.rkt   |  3 +++
 collects/racket/private/for.rkt | 26 ++++++++++++++++++++++++++
 collects/tests/racket/for.rktl  |  7 +++++++
 3 files changed, 36 insertions(+)

diff --git a/collects/racket/generator.rkt b/collects/racket/generator.rkt
index 1ce50ac7e4..8932b797ac 100644
--- a/collects/racket/generator.rkt
+++ b/collects/racket/generator.rkt
@@ -112,6 +112,9 @@
      (in-producer (generator () body0 body ... stop-value) stop-value)])
   (lambda (stx)
     (syntax-case stx ()
+      [(() (_ body0 body ...))
+       #'[()
+          (in-producer (generator () body0 body ... stop-value) stop-value)]]
       [((id ...) (_ body0 body ...))
        (with-syntax ([(stops ...) (syntax-case #'((id stop-value) ...) ()
                                     [((x v) ...) #'(v ...)])])
diff --git a/collects/racket/private/for.rkt b/collects/racket/private/for.rkt
index 5cd17719bd..925878d06b 100644
--- a/collects/racket/private/for.rkt
+++ b/collects/racket/private/for.rkt
@@ -1281,6 +1281,32 @@
                #t
                ;; loop args
                ())])]
+        [[() (_ producer stop more ...)]
+         (with-syntax ([(more* ...) (generate-temporaries #'(more ...))])
+           #'[()
+              (:do-in
+                ([(producer*) producer] [(more*) more] ...
+                 [(stop?) (let ([s stop])
+                           (if (procedure? s)
+                             s
+                             (lambda (args)
+                               (and (not (null? args))
+                                    (eq? (car args) s)))))])
+               ;; outer check
+               #t
+               ;; loop bindings
+               ()
+               ;; pos check
+               #t
+               ;; inner bindings
+               ([(check) (call-with-values (lambda () (producer* more* ...))
+                                           (lambda vs vs))])
+               ;; pre guard
+               (not (stop? check))
+               ;; post guard
+               #t
+               ;; loop args
+               ())])]
         ;; multiple-values version
         [[(id ...) (_ producer stop more ...)]
          (with-syntax ([(more* ...) (generate-temporaries #'(more ...))])
diff --git a/collects/tests/racket/for.rktl b/collects/tests/racket/for.rktl
index cd0ed75a4a..9123a7cfd6 100644
--- a/collects/tests/racket/for.rktl
+++ b/collects/tests/racket/for.rktl
@@ -242,6 +242,7 @@
       (for/list ([(x i) (in-indexed (in-generator (yield 1) (yield 2) (yield 3)))])
         (list x i)))
 
+;; test multiple values for in-generator
 (test '[(1 2) (3 4)] 'for*-generator
       (for*/list ([(n after)
               (in-generator
@@ -249,6 +250,12 @@
                 (yield 3 4))])
             (list n after)))
 
+;; test 0-ary yields
+(test '(0 1 2) 'no-bind-in-generator
+   (for/list ([() (in-generator (yield) (yield) (yield))]
+              [i (in-naturals)])
+     i))
+
 (let ([helper (lambda (i)
                 (yield (add1 i)))])
   (test '(1 2 3) 'parameterized-yield