A-M baby

Task/First-class-functions/Java/first-class-functions-2.java

@@ -0,0 +1,36 @@
+import java.util.ArrayList;
+import java.util.function.Function;
+
+public class FirstClass{
+	
+	public static <A,B,C> Function<A, C> compose(
+			final Function<B, C> f, final Function<A, B> g) {
+		return new Function<A, C>() {
+			@Override public C apply(A x) {
+				return f.apply(g.apply(x));
+			}
+		};
+	}
+	
+	public static void main(String[] args){
+		ArrayList<Function<Double, Double>> functions = new ArrayList<>();
+		
+		functions.add(Math::cos);
+		functions.add(Math::tan);
+		functions.add(x -> x * x);
+		
+		ArrayList<Function<Double, Double>> inverse = new ArrayList<>();
+		
+		inverse.add(Math::acos);
+		inverse.add(Math::atan);
+		inverse.add(Math::sqrt);
+		System.out.println("Compositions:");
+		for(int i = 0; i < functions.size(); i++){
+			System.out.println(compose(functions.get(i), inverse.get(i)).apply(0.5));
+		}
+		System.out.println("Hard-coded compositions:");
+		System.out.println(Math.cos(Math.acos(0.5)));
+		System.out.println(Math.tan(Math.atan(0.5)));
+		System.out.println(Math.pow(Math.sqrt(0.5), 2));
+	}
+}