--- a/Main/jungle-main/util/DefaultEither.cs	Sat Jan 28 19:12:18 2017 +0900
+++ b/Main/jungle-main/util/DefaultEither.cs	Tue Feb 07 20:50:50 2017 +0900
@@ -3,16 +3,6 @@
 	private A theA;
 	private B theB;
 
-	public void SetB (B b) {
-		this.theB = b;
-	}
-
-	public void SetA (A a) {
-		this.theA = a;
-	}
-
-	public delegate B Func (B b);
-
 	public DefaultEither(A _theA, B _theB){
 		theA = _theA;
 		theB = _theB;
@@ -51,12 +41,18 @@
 		return theB != null;
 	}
 
-	public Either<A, B> fmap(System.Func<B, B> f, Either<A,B> e) {
-		if (e.isA ()) {
-			return e;
+	public Either<A, B> fmap(System.Func<B, B> f) {
+		if (isA ()) {
+			return this;
 		}
-		this.SetB (f (e.b()));
-		return this;
+		return newB(f(b()));
 	}
 
+	public Either<A, B> bind (System.Func<B, Either<A, B>> f) {
+		if (isA ()) {
+			return this;
+		}
+
+		return f (b ());
+	}
 }