add predicates is[Something] for union type

paldepind · Nov 16, 2016 · 3eb4315 · 3eb4315
1 parent 6c3c3c9
commit 3eb4315
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diff --git a/test/index.js b/test/index.js
@@ -118,6 +118,17 @@ describe('union type', function() {
       assert.equal(p[1], undefined);
     });
   });
+  describe('predicate', function() {
+    it('can use predicate to check type', function() {
+      var Maybe = Type({Just: [T], Nothing: []});
+      var OtherMaybe = Type({Just: [T]});
+      var just1 = Maybe.Just(1)
+      assert.equal(Maybe.isJust(just1), true);
+      assert.equal(Maybe.isNothing(just1), false);
+      assert.equal(Maybe.isNothing(just1), false);
+      assert.equal(OtherMaybe.isJust(just1), false);
+    })
+  });
   describe('type methods', function() {
     it('can add instance methods', function() {
       var Maybe = Type({Just: [T], Nothing: []});

diff --git a/union-type.js b/union-type.js
@@ -75,6 +75,9 @@ function constructor(group, name, fields) {
     return val;
   }
   group[name] = curryN(keys.length, construct);
+  group['is' + name] = function(value) {
+    return group.prototype.isPrototypeOf(value) && name === value._name
+  }
   if (keys !== undefined) {
     group[name+'Of'] = function(obj) {
       return construct.apply(undefined, extractValues(keys, obj));