From be7032ad2b30e9b868bbec039ccdb743dc901fdc Mon Sep 17 00:00:00 2001
From: Jichao Ouyang <oyanglulu@gmail.com>
Date: Wed, 11 May 2016 23:23:44 +0800
Subject: [PATCH] A handy ListOf Type

simple ListOf[T] Type as mention in #32

validate it is a Array and each element type to be T
---
 test/index.js | 12 ++++++++++++
 union-type.js | 15 +++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/test/index.js b/test/index.js
index d3f83d1..1abd32a 100644
--- a/test/index.js
+++ b/test/index.js
@@ -61,6 +61,18 @@ describe('union type', function() {
       }, /wrong value/);
     });
   });
+  it('array of types', function() {
+    var Point = Type({Point: [Number, Number]});
+    var Shape = Type({Shape: [Type.ListOf(Point)]}).Shape;
+    assert.throws(function(){
+      Shape([1,Point.Point(1,2),3]);
+    }, /wrong value/);
+    assert.throws(function(){
+      Shape([Point.Point(1,2), Point.Point('3',1)]);
+    }, /wrong value/)
+    Shape([Point.Point(1,2), Point.Point(1,2), Point.Point(1,2)]);
+    Shape([]);
+  });
   it('nest types', function() {
     var Point = Type({Point: [isNumber, isNumber]});
     var Shape = Type({Circle: [Number, Point],
diff --git a/union-type.js b/union-type.js
index 76b59e0..5449faf 100644
--- a/union-type.js
+++ b/union-type.js
@@ -127,4 +127,19 @@ function Type(desc) {
 
 Type.check = true;
 
+Type.ListOf = function (T) {
+  var ListOf = Type({List:[Array], HeadTail:[T, Array]});
+  var validate = ListOf.case({
+    List: function (array) {
+      return array.length == 0 || validate(ListOf.HeadTail(array[0],array.slice(1)));
+    },
+    HeadTail: function (head, tail) {
+      return tail.slice(1).length == 0 || validate(ListOf.HeadTail(tail[0], tail.slice(1)));
+    }
+  });
+  return function(array) {
+    return validate(ListOf.List(array));
+  }
+}
+
 module.exports = Type;