added a nullary case to compose

svn: r14697

collects/scheme/private/list.ss

@@ -232,7 +232,7 @@
 
   (define compose
     (case-lambda
-      [(f) (if (procedure? f) 
+      [(f) (if (procedure? f)
                f
                (raise-type-error 'compose "procedure" f))]
       [(f g)
@@ -247,6 +247,7 @@
                    (call-with-values (lambda () (g a)) f))
                  (lambda args
                    (call-with-values (lambda () (apply g args)) f)))))]
+      [() values]
       [(f . more)
        (if (procedure? f)
            (let ([m (apply compose more)])

collects/scribblings/reference/procedures.scrbl

@@ -38,7 +38,8 @@ Returns a procedure that composes the given functions, applying the
 last @scheme[proc] first and the first @scheme[proc] last. The
 composed functions can consume and produce any number of values, as
 long as each function produces as many values as the preceding
-function consumes.
+function consumes.  When no @scheme[proc] arguments are given, the
+result is @scheme[values].
 
 @mz-examples[
 ((compose - sqrt) 10)

collects/tests/mzscheme/function.ss

@@ -14,6 +14,7 @@
 (test 'hi (compose (case-lambda [(x) 'bye][(y z) 'hi]) (lambda () (values 1 2))))
 (test 'ok (compose (lambda () 'ok) (lambda () (values))))
 (test 'ok (compose (lambda () 'ok) (lambda (w) (values))) 5)
+(test 0 (compose) 0)
 (test-values '(1 2 3) (lambda () ((compose (lambda (x) (values x (add1 x) (+ x 2))) (lambda (y) y)) 1)))
 
 (err/rt-test (compose 5))