Add array-empty?

Closes #969.

Author: ashinn

lib/srfi/231.sld

@@ -37,6 +37,7 @@
    storage-class-data? storage-class-data->body
    ;; Arrays
    make-array array? array-domain array-getter array-dimension
+   array-empty?
    mutable-array? array-setter specialized-array-default-safe?
    specialized-array-default-mutable? make-specialized-array
    make-specialized-array-from-data

lib/srfi/231/base.scm

@@ -311,6 +311,9 @@
 (define (array-dimension a)
   (interval-dimension (array-domain a)))
 
+(define (array-empty? a)
+  (interval-empty? (array-domain a)))
+
 (define (mutable-array? x)
   (and (array? x) (array-setter x) #t))
 

lib/srfi/231/base.sld

@@ -37,7 +37,7 @@
    ;; Arrays
    make-array array? array-domain array-getter array-dimension
    mutable-array? array-setter specialized-array-default-safe?
-   specialized-array-default-mutable?
+   specialized-array-default-mutable? array-empty?
    make-specialized-array make-specialized-array-from-data
    specialized-array? array-storage-class array-indexer array-body
    array-safe? array-coeffs array-adjacent? array-packed?