Data commit

Task/Queue-Definition/E/queue-definition.e

@@ -0,0 +1,27 @@
+def makeQueue() {
+  def [var head, var tail] := Ref.promise()
+
+  def writer {
+    to enqueue(value) {
+      def [nh, nt] := Ref.promise()
+      tail.resolve([value, nh])
+      tail := nt
+    }
+  }
+
+  def reader {
+    to empty() { return !Ref.isResolved(head) }
+
+    to dequeue(whenEmpty) {
+      if (Ref.isResolved(head)) {
+        def [value, next] := head
+        head := next
+        return value
+      } else {
+        throw.eject(whenEmpty, "pop() of empty queue")
+      }
+    }
+  }
+
+  return [reader, writer]
+}