stream*: allow 1 argument

pkgs/racket-doc/scribblings/reference/sequences.scrbl

@@ -1073,8 +1073,8 @@ stream, but plain lists can be used as streams, and functions such as
   @racket[empty-stream].
 }
 
-@defform[(stream* expr ...)]{
-  A shorthand for nested @racket[stream-cons]es, but the final @racket[expr]
+@defform[(stream* expr ... rest-expr)]{
+  A shorthand for nested @racket[stream-cons]es, but the @racket[rest-expr]
   must be a stream, and it is used as the rest of the stream instead of
   @racket[empty-stream]. Similar to @racket[list*] but for streams.
 

pkgs/racket-test-core/tests/racket/stream.rktl

@@ -35,10 +35,14 @@
 (test 4 stream-ref one-to-four 3)
 (test 2 'stream (stream-length (stream 1 (/ 0))))
 (test 'a 'stream (stream-first (stream 'a (/ 0))))
+(test 1 'stream* (stream-first (stream* (stream 1))))
 (test 2 'stream* (stream-length (stream* 1 (stream (/ 0)))))
 (test 'a 'stream* (stream-first (stream* 'a (stream (/ 0)))))
 (test 4 'stream* (stream-length (stream* 'a 'b 'c (stream (/ 0)))))
 (test 'c 'stream* (stream-first (stream-rest (stream-rest (stream* 'a 'b 'c (stream (/ 0)))))))
+(err/rt-test (stream* 2) exn:fail:contract? "stream*")
+(test #true 'stream* (stream? (stream* 1 0)))
+(err/rt-test (stream-length (stream* 1 2)) exn:fail:contract? "stream*")
 
 ;; make sure stream operations work on lists
 (test #t stream-empty? '())

racket/collects/racket/stream.rkt

@@ -70,11 +70,16 @@
 
 (define-syntax stream*
   (syntax-rules ()
-    [(_ hd tl)
-     (stream-cons hd tl)]
+    [(_ tl)
+     (assert-stream? 'stream* tl)]
     [(_ hd tl ...)
      (stream-cons hd (stream* tl ...))]))
 
+(define (assert-stream? who st)
+  (if (stream? st)
+    st
+    (raise-argument-error who "stream?" st)))
+
 (define (stream->list s)
   (for/list ([v (in-stream s)]) v))