Chapter 2

fpinjava-parent/fpinjava-usingfunctions-exercises/src/main/java/com/fpinjava/functions/exercise02_01/BiFunctionInterface.java

@@ -0,0 +1,6 @@
+package com.fpinjava.functions.exercise02_01;
+
+interface BiFunctionInterface<T, U, V> {
+    V biApply(T t, U u);
+
+}

fpinjava-parent/fpinjava-usingfunctions-exercises/src/main/java/com/fpinjava/functions/exercise02_01/FunctionExamples.java

@@ -2,24 +2,51 @@
 
 public class FunctionExamples {
 
-  public static final Function<Integer, Integer> triple = new Function<Integer, Integer>() {
+    public static final Function<Integer, Integer> triple() {
+        return
+                new Function<Integer, Integer>() {
 
-    @Override
-    public Integer apply(Integer arg) {
-      return arg * 3;
+                    @Override
+                    public Integer apply(Integer arg) {
+                        return arg * 3;
+                    }
+                };
     }
-  };
 
-  public static final Function<Integer, Integer> square = new Function<Integer, Integer>() {
+    public static final Function<Integer, Integer> triple2 = arg -> arg * 3;
 
-    @Override
-    public Integer apply(Integer arg) {
-      return arg * arg;
+    public static final Function<Integer, Integer> square() {
+        return new Function<Integer, Integer>() {
+
+            @Override
+            public Integer apply(Integer arg) {
+                return arg * arg;
+            }
+        };
+    }
+
+    public static final Function<Integer, Integer> square2 = arg -> arg * arg;
+
+    public static final Function<Integer, Integer> compose(final Integer x, final Integer y) {
+        return arg -> x + y;
+    }
+
+
+    public static final Function<Integer, Integer> compose(final Function<Integer, Integer> x, final Function<Integer, Integer> y) {
+        return arg -> x.apply(y.apply(arg));
     }
-  };
 
-  public static final Function<Integer, Integer> compose(final Function<Integer, Integer> f1,
-                                                         final Function<Integer, Integer> f2) {
-    throw new RuntimeException("To be implemented.");
-  }
+
+    //public static final TriFunction<Function<>, Function, Function, Integer> compose2 =  f1 -> f2 -> arg -> f1.apply(f2.apply(arg));
+    public static final TriFunction<Function<Integer, Integer>, Function<Integer, Integer>, Integer, Integer> compose3 =  (f1, f2, arg) -> f1.apply(f2.apply(arg));
+
+    public static final TriFunction<Integer, Integer, Integer, Integer> compose4 =  (f1, f2, arg) -> f1 + 0;
+
+
+    public static final Function<Integer, Integer> compose2(Function f1, Function f2) { return arg -> triple2.apply(square2.apply(arg));};
+
+    public static final Function<Integer, Integer> compose201(Function<Integer, Integer> f1, Function<Integer, Integer> f2) { return arg -> f1.apply(f2.apply(arg));};
+
+    public static final TriFunction<Function<Integer, Integer>, Function<Integer, Integer>, Integer, Integer> compose301 =  (f1, f2, arg) -> f1.apply(f2.apply(arg));
+
 }

fpinjava-parent/fpinjava-usingfunctions-exercises/src/main/java/com/fpinjava/functions/exercise02_01/HigherComposeOptions.java

@@ -0,0 +1,20 @@
+package com.fpinjava.functions.exercise02_01;
+
+public class HigherComposeOptions <T, U, V> {
+
+    //using params
+    public static <T, U, V> Function<T, V> higherCompose1(Function<U, V> f1, Function<T, U> f2) {
+        return arg -> f1.apply(f2.apply(arg));
+    }
+
+    //using params of the lambda
+    public final TriFunction<Function<U, V>, Function<T, U>, T, V>
+            higherCompose3 = (f1, f2, arg) -> f1.apply(f2.apply(arg));
+
+
+    //currying
+    public static <T, U, V> Function<Function<U, V>, Function<Function<T, U>, Function<T, V>>> higherCompose3() {
+        return f1 -> f2 -> arg -> f1.apply(f2.apply(arg));
+    }
+
+}

fpinjava-parent/fpinjava-usingfunctions-exercises/src/main/java/com/fpinjava/functions/exercise02_01/TriFunction.java

@@ -0,0 +1,5 @@
+package com.fpinjava.functions.exercise02_01;
+
+interface TriFunction<T, U, V, R>{
+    R triApply(T t, U u, V v);
+}

fpinjava-parent/fpinjava-usingfunctions-exercises/src/main/java/com/fpinjava/functions/exercise02_02/FunctionExamples.java

@@ -2,12 +2,12 @@
 
 public class FunctionExamples {
 
-  public static final Function<Integer, Integer> triple = x -> x * 3;
+    public static final Function<Integer, Integer> triple = x -> x * 3;
 
-  public static final Function<Integer, Integer> square = x -> x * x;
+    public static final Function<Integer, Integer> square = x -> x * x;
 
-  public static final Function<Integer, Integer> compose(final Function<Integer, Integer> f1,
-                                                         final Function<Integer, Integer> f2) {
-    throw new RuntimeException("To be implemented.");
-  }
+    public static final Function<Integer, Integer> compose(final Function<Integer, Integer> f1,
+                                                           final Function<Integer, Integer> f2) {
+        return x -> f1.apply(f2.apply(x));
+    }
 }

fpinjava-parent/fpinjava-usingfunctions-exercises/src/main/java/com/fpinjava/functions/exercise02_03/FunctionExamples.java

@@ -3,9 +3,10 @@
 
 public class FunctionExamples {
 
-  public static final Function<Integer, Function<Integer, Integer>> add = null; // To be implemented
+  //why does x is highlighted by intelliJ as purple with under score?
+  public static final Function<Integer, Function<Integer, Integer>> add = x -> y -> x + y;
 
-  public static final BinaryOperator add2 =  null; // To be implemented
+  public static final BinaryOperator add2 =  x -> y -> x + y;
 
-  public static final BinaryOperator mult =  null; // To be implemented
+  public static final BinaryOperator mult =  x -> y -> x * y;
 }

fpinjava-parent/fpinjava-usingfunctions-exercises/src/main/java/com/fpinjava/functions/exercise02_04/FunctionExamples.java

@@ -7,7 +7,7 @@ public class FunctionExamples {
   public static final Function<Integer, Integer> square = x -> x * x;
 
   public static final Function<Function<Integer, Integer>, Function<Function<Integer, Integer>,
-                                        Function<Integer, Integer>>> compose = null; // To be implemented
+                                        Function<Integer, Integer>>> compose = x -> y -> z -> x.apply(y.apply(z));
 
   public static final Function<Integer, Integer> f = compose.apply(square).apply(triple);
 }

fpinjava-parent/fpinjava-usingfunctions-exercises/src/main/java/com/fpinjava/functions/exercise02_05/Function.java

@@ -4,7 +4,44 @@ public interface Function<T, U> {
 
   U apply(T arg);
 
-  static <T, U, V> Function<Function<U, V>, Function<Function<T, U>, Function<T, V>>> higherCompose() {
-    throw new RuntimeException("To be implemented.");
+
+
+  static <T, U, V> Function<Function<U, V>, Function<Function<T, U>, Function<T, V>>> higherCompose(){
+    return f1 -> f2 -> arg -> f1.apply(f2.apply(arg));
+  }
+
+
+    static  Function<Function<String, Boolean>, Function<Function<Integer, String>, Function<Integer, Boolean>>> higherCompose4(){
+        return f1 -> f2 -> arg -> f1.apply(f2.apply(arg));
+    }
+
+    //F0 - Boolean T
+    //F1 - Integer U
+    //F2 - Boolean V
+    //Arg - Character W
+
+  static <T> Function<Function<T, T>, Function<T, T>> higherCompose2(){
+    return f1 -> arg -> f1.apply(arg);
   }
+
+  static <T> Function<T, Integer> higherCompose3(){
+    final Function<T, Integer> tIntegerFunction = arg -> 0;
+    return tIntegerFunction;
+  }
+
+//  static <T, U, V> Function<> higherCompose2() {
+//    return x -> y -> z -> x.apply(y.apply(z));
+//  }
+//
+//  static <T, U, V> Function<T, Function<>> higherCompose2() {
+//    return x -> y -> z -> x.apply(y.apply(z));
+//  }
+//
+//  static <T, U, V> Function<Function<>, Function<>> higherCompose2() {
+//    return x -> y -> z -> x.apply(y.apply(z));
+//  }
+//
+//  static <T, U, V> Function<Function<>, Function<Function<>, Function<>>> higherCompose2() {
+//    return x -> y -> z -> x.apply(y.apply(z));
+//  }
 }

fpinjava-parent/fpinjava-usingfunctions-exercises/src/main/java/com/fpinjava/functions/exercise02_06/Function.java

@@ -10,6 +10,6 @@ static <T, U, V> Function<Function<U, V>, Function<Function<T, U>, Function<T, V
   }
 
   static <T, U, V> Function<Function<T, U>, Function<Function<U, V>, Function<T, V>>> higherAndThen() {
-    throw new RuntimeException("To be implemented.");
+    return f -> g -> x -> g.apply(f.apply(x));
   }
 }