Add isEmpty to Sequence.

Thanks, Michel and Thorbjørn!

builtin/core.wren

@@ -52,6 +52,8 @@ class Sequence {
     }
   }
 
+  isEmpty { iterate(null) ? false : true }
+
   map(transformation) { new MapSequence(this, transformation) }
 
   where(predicate) { new WhereSequence(this, predicate) }

doc/site/core/sequence.markdown

@@ -61,6 +61,13 @@ Iterates over the sequence, passing each element to the given `function`.
     :::dart
     ["one", "two", "three"].each {|word| IO.print(word) }
 
+### **isEmpty**
+
+Returns whether the sequence contains any elements.
+
+This can be more efficient that `count == 0` because this does not iterate over
+the entire sequence.
+
 ### **join**(sep)
 
 Returns a string representation of the sequence. The string representations of

src/vm/wren_core.c

@@ -66,6 +66,8 @@ static const char* coreLibSource =
 "    }\n"
 "  }\n"
 "\n"
+"  isEmpty { iterate(null) ? false : true }\n"
+"\n"
 "  map(transformation) { new MapSequence(this, transformation) }\n"
 "\n"
 "  where(predicate) { new WhereSequence(this, predicate) }\n"

test/core/sequence/is_empty.wren

@@ -0,0 +1,10 @@
+IO.print([].isEmpty) // expect: true
+IO.print([1].isEmpty) // expect: false
+
+class InfiniteSequence is Sequence {
+  iterate(iterator) { true }
+  iteratorValue(iterator) { iterator }
+}
+
+// Should not try to iterate the whole sequence.
+IO.print((new InfiniteSequence).isEmpty) // expect: false