vector-copy now works for empty vectors

svn: r16930

collects/scheme/vector.ss

@@ -20,6 +20,16 @@
   (unless (exact-nonnegative-integer? start)
     (raise-type-error 'vector-copy "non-negative exact integer" 1 start))
   (let ([len (vector-length v)])
+    (cond
+      [(= len 0)
+       (unless (and (= start 0)
+                    (= end 0))
+         (raise-mismatch-error
+          'vector-copy
+          (format "start index and end index must both be 0 for empty vectors, got ~e and ~e"
+                  start len)))
+       (vector)]
+      [else
        (unless (and (<= 0 start) (< start len))
          (raise-mismatch-error
           'vector-copy
@@ -32,7 +42,7 @@
           (format "end index ~e out of range [~e, ~e] for vector ~e"
                   end start len v)
           v))
-    (vector-copy* v start end)))
+       (vector-copy* v start end)])))
 
 ;; do vector-map, putting the result in `target'
 ;; length is passed to save the computation