Add vector-empty? (#2695)

* Add vector-empty?

* Add tests for vector-empty?

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

@@ -30,6 +30,9 @@ a number between the @litchar{#} and
 
 Returns @racket[#t] if @racket[v] is a vector, @racket[#f] otherwise.}
 
+@defproc[(vector-empty? [v vector?]) boolean?]{
+
+Returns @racket[#t] if @racket[v] is empty (i.e. its length is 0), @racket[#f] otherwise.}
 
 @defproc[(make-vector [size exact-nonnegative-integer?]
                       [v any/c 0]) vector?]{

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

@@ -61,6 +61,12 @@
 (err/rt-test (vector-fill! '(1 2 3) 0))
 
 
+;; ---------- vector-empty? ----------
+(test #f vector-empty? '#(a))
+(test #f vector-empty? '#(()))
+(test #f vector-empty? '#(#()))
+(test #t vector-empty? '#())
+
 
 ;; ---------- vector-take/drop[-right] ----------
 (let ()

racket/collects/racket/vector.rkt

@@ -1,6 +1,7 @@
 #lang racket/base
 
-(provide vector-set*! vector-copy vector-map vector-map! vector-append
+(provide vector-empty? vector-set*! vector-copy
+         vector-map vector-map! vector-append
          vector-take vector-drop vector-split-at
          vector-take-right vector-drop-right vector-split-at-right
          vector-filter vector-filter-not
@@ -11,7 +12,12 @@
          (for-syntax racket/base)
          (rename-in (except-in "private/sort.rkt" sort)
                     [vector-sort! raw-vector-sort!]
-                    [vector-sort raw-vector-sort])) 
+                    [vector-sort raw-vector-sort]))
+
+(define (vector-empty? v)
+  (unless (vector? v)
+    (raise-argument-error 'vector-empty? "vector?" v))
+  (zero? (vector-length v)))
 
 (define (vector-set*! v . pairs)
   (unless (even? (length pairs))