Creata astrazione della struttura if...then...else...

functional-programming-java/src/main/java/org/gym/fp/fpjava/Main.java

@@ -1,11 +1,13 @@
 package org.gym.fp.fpjava;
 
+import org.gym.fp.fpjava.demo.AbstractControlStructureDemo;
 import org.gym.fp.fpjava.demo.FunctionDemo;
 
 public class Main {
 
     public static void main(String[] args) {
         FunctionDemo.run();
+        AbstractControlStructureDemo.run();
     }
 
 }

functional-programming-java/src/main/java/org/gym/fp/fpjava/demo/AbstractControlStructureDemo.java

@@ -0,0 +1,49 @@
+package org.gym.fp.fpjava.demo;
+
+import org.gym.fp.fpjava.type.Effect;
+import org.gym.fp.fpjava.type.Function;
+import org.gym.fp.fpjava.type.Result;
+
+import java.util.regex.Pattern;
+
+import static org.gym.fp.fpjava.type.Case.match;
+import static org.gym.fp.fpjava.type.Case.when;
+
+public class AbstractControlStructureDemo {
+
+    public static void run() {
+        doEmailValidationDemo();
+    }
+
+    private static void doEmailValidationDemo() {
+        validate("this.is@my.email");
+        validate(null);
+        validate("");
+        validate("john.doe@acme.com");
+    }
+
+    private static void validate(String email) {
+        final EmailValidation validation = new EmailValidation();
+        final Function<String, Result<String>> emailChecker = validation.emailChecker;
+        final Effect<String> success = validation.success;
+        final Effect<String> failure = validation.failure;
+        emailChecker.apply(email).bind(success, failure);
+    }
+}
+
+class EmailValidation {
+    public final Pattern emailPattern =
+            Pattern.compile("^[a-z0-9._%+-]+@[a-z0-9.-]+\\.[a-z]{2,4}$");
+
+    public final Effect<String> success =
+            email -> System.out.println("Verification mail sent to " + email);
+
+    public final Effect<String> failure =
+            msg -> System.err.println("Error message logged: " + msg);
+
+    public final Function<String, Result<String>> emailChecker = s -> match(
+            when(() -> Result.success(s)),
+            when(() -> s == null, () -> Result.failure("email must not be null")),
+            when(() -> s.length() == 0, () -> Result.failure("email must not be empty")),
+            when(() -> !emailPattern.matcher(s).matches(), () -> Result.failure("email " + s + " is invalid")));
+}

functional-programming-java/src/main/java/org/gym/fp/fpjava/type/Case.java

@@ -0,0 +1,31 @@
+package org.gym.fp.fpjava.type;
+
+public class Case<T> extends Tuple<Supplier<Boolean>, Supplier<Result<T>>> {
+
+    public Case(Supplier<Boolean> booleanSupplier, Supplier<Result<T>> resultSupplier) {
+        super(booleanSupplier, resultSupplier);
+    }
+
+    private static class DefaultCase<T> extends Case<T> {
+
+        public DefaultCase(Supplier<Boolean> booleanSupplier, Supplier<Result<T>> resultSupplier) {
+            super(booleanSupplier, resultSupplier);
+        }
+    }
+
+    public static <T> Case<T> when(Supplier<Boolean> condition, Supplier<Result<T>> value) {
+        return new Case<>(condition, value);
+    }
+
+    public static <T> DefaultCase<T> when(Supplier<Result<T>> value) {
+        return new DefaultCase<>(() -> true, value);
+    }
+
+    @SafeVarargs
+    public static <T> Result<T> match(DefaultCase<T> defaultCase, Case<T>... matchers) {
+        for (Case<T> aCase : matchers) {
+            if (aCase._1.get()) return aCase._2.get();
+        }
+        return defaultCase._2.get();
+    }
+}

functional-programming-java/src/main/java/org/gym/fp/fpjava/type/Effect.java

@@ -0,0 +1,5 @@
+package org.gym.fp.fpjava.type;
+
+public interface Effect<T> {
+    void apply(T t);
+}

functional-programming-java/src/main/java/org/gym/fp/fpjava/type/Executable.java

@@ -0,0 +1,5 @@
+package org.gym.fp.fpjava.type;
+
+public interface Executable {
+    void exec();
+}

functional-programming-java/src/main/java/org/gym/fp/fpjava/type/Result.java

@@ -0,0 +1,43 @@
+package org.gym.fp.fpjava.type;
+
+public interface Result<T> {
+    void bind(Effect<T> success, Effect<T> failure);
+
+    static <T> Result<T> failure(String message) {
+        return new Failure<>(message);
+    }
+
+    static <T> Result<T> success(T value) {
+        return new Success<>(value);
+    }
+
+    class Success<T> implements Result<T> {
+        private final T value;
+
+        public Success(T value) {
+            this.value = value;
+        }
+
+        @Override
+        public void bind(Effect<T> success, Effect<T> failure) {
+            success.apply(value);
+        }
+    }
+
+    class Failure<T> implements Result<T> {
+        private final String errorMessage;
+
+        public Failure(String msg) {
+            this.errorMessage = msg;
+        }
+
+        public String getMessage() {
+            return this.errorMessage;
+        }
+
+        @Override
+        public void bind(Effect success, Effect failure) {
+            failure.apply(errorMessage);
+        }
+    }
+}

functional-programming-java/src/main/java/org/gym/fp/fpjava/type/Supplier.java

@@ -0,0 +1,5 @@
+package org.gym.fp.fpjava.type;
+
+public interface Supplier<T> {
+    T get();
+}

functional-programming-java/src/main/java/org/gym/fp/fpjava/type/Tuple.java

@@ -1,8 +1,8 @@
 package org.gym.fp.fpjava.type;
 
 public class Tuple<A, B> {
-    private final A _1;
-    private final B _2;
+    public final A _1;
+    public final B _2;
 
     public Tuple(A first, B second) {
         this._1 = first;