A-M baby

Task/Function-composition/Java/function-composition-1.java

@@ -0,0 +1,33 @@
+public class Compose {
+
+    // Java doesn't have function type so we define an interface
+    // of function objects instead
+    public interface Fun<A,B> {
+        B call(A x);
+    }
+
+    public static <A,B,C> Fun<A,C> compose(final Fun<B,C> f, final Fun<A,B> g) {
+        return new Fun<A,C>() {
+            public C call(A x) {
+                return f.call(g.call(x));
+            }
+        };
+    }
+
+    public static void main(String[] args) {
+        Fun<Double,Double> sin = new Fun<Double,Double>() {
+            public Double call(Double x) {
+                return Math.sin(x);
+            }
+        };
+        Fun<Double,Double> asin = new Fun<Double,Double>() {
+            public Double call(Double x) {
+                return Math.asin(x);
+            }
+        };
+
+        Fun<Double,Double> sin_asin = compose(sin, asin);
+
+        System.out.println(sin_asin.call(0.5)); // prints "0.5"
+    }
+}