Pattern combinator

combinator/README.md

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+---
+layout: pattern
+title: Combinator
+folder: combinator
+permalink: /patterns/combinator/
+categories: Behavioral
+tags:
+ - Functional
+ - Reactive
+ - Idiom
+---
+
+## Also known as
+Composition pattern
+
+## Intent
+The functional pattern representing a style of organizing libraries centered around the idea of combining functions.  
+Putting it simply, there is some type T, some functions for constructing "primitive" values of type T, 
+and some "combinators" which can combine values of type T in various ways to build up more complex values of type T.
+
+
+## Applicability
+Use the combinator pattern when:
+- You are able to create a more complex value from more plain values but having the same type(a combination of them)
+
+## Real world examples
+- java.util.function.Function#compose
+- java.util.function.Function#andThen
+
+## Credits
+- [Example for java](https://gtrefs.github.io/code/combinator-pattern/)
+- [Combinator pattern](https://wiki.haskell.org/Combinator_pattern)
+- [Combinatory logic](https://wiki.haskell.org/Combinatory_logic)

combinator/pom.xml

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+<?xml version="1.0"?>
+<!--
+
+    The MIT License
+    Copyright © 2014-2019 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.23.0-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>combinator</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+</project>

combinator/src/main/java/com/iluwatar/combinator/CombinatorApp.java

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+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.combinator;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * The functional pattern representing a style of organizing libraries
+ * centered around the idea of combining functions.
+ * Putting it simply, there is some type T, some functions
+ * for constructing "primitive" values of type T,
+ * and some "combinators" which can combine values of type T
+ * in various ways to build up more complex values of type T.
+ * The class {@link Finder} defines a simple function {@link Finder#find(String)}
+ * and connected functions
+ * {@link Finder#or(Finder)},
+ * {@link Finder#not(Finder)},
+ * {@link Finder#and(Finder)}
+ * Using them the became possible to get more complex functions {@link Finders}
+ */
+public class CombinatorApp {
+
+  /**
+   * Logger.
+   */
+  private static final Logger LOGGER = LoggerFactory.getLogger(CombinatorApp.class);
+
+  /**
+   * main.
+   * @param args args
+   */
+  public static void main(String[] args) {
+    var queriesOr = new String[]{"many", "Annabel"};
+    var finder = Finders.expandedFinder(queriesOr);
+    var res = finder.find(text());
+    LOGGER.info("the result of expanded(or) query[{}] is {}", queriesOr, res);
+
+    var queriesAnd = new String[]{"Annabel", "my"};
+    finder = Finders.specializedFinder(queriesAnd);
+    res = finder.find(text());
+    LOGGER.info("the result of specialized(and) query[{}] is {}", queriesAnd, res);
+
+    finder = Finders.advancedFinder("it was","kingdom","sea");
+    res = finder.find(text());
+    LOGGER.info("the result of advanced query is {}", res);
+
+    res = Finders.filteredFinder(" was ", "many", "child").find(text());
+    LOGGER.info("the result of filtered query is {}", res);
+
+
+  }
+
+  private static String text() {
+    return
+        "It was many and many a year ago,\n"
+            + "In a kingdom by the sea,\n"
+            + "That a maiden there lived whom you may know\n"
+            + "By the name of ANNABEL LEE;\n"
+            + "And this maiden she lived with no other thought\n"
+            + "Than to love and be loved by me.\n"
+            + "I was a child and she was a child,\n"
+            + "In this kingdom by the sea;\n"
+            + "But we loved with a love that was more than love-\n"
+            + "I and my Annabel Lee;\n"
+            + "With a love that the winged seraphs of heaven\n"
+            + "Coveted her and me.";
+  }
+
+}

combinator/src/main/java/com/iluwatar/combinator/Finder.java

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+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.combinator;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * Functional interface to find lines in text.
+ */
+public interface Finder {
+
+  /**
+   * The function to find lines in text.
+   * @param text full tet
+   * @return result of searching
+   */
+  List<String> find(String text);
+
+  /**
+   * Simple implementation of function {@link #find(String)}.
+   * @param word for searching
+   * @return this
+   */
+  static Finder contains(String word) {
+    return txt -> Stream.of(txt.split("\n"))
+        .filter(line -> line.toLowerCase().contains(word.toLowerCase()))
+        .collect(Collectors.toList());
+  }
+
+  /**
+   * combinator not.
+   * @param notFinder finder to combine
+   * @return new finder including previous finders
+   */
+  default Finder not(Finder notFinder) {
+    return txt -> {
+      List<String> res = this.find(txt);
+      res.removeAll(notFinder.find(txt));
+      return res;
+    };
+  }
+
+  /**
+   * combinator or.
+   * @param orFinder finder to combine
+   * @return new finder including previous finders
+   */
+  default Finder or(Finder orFinder) {
+    return txt -> {
+      List<String> res = this.find(txt);
+      res.addAll(orFinder.find(txt));
+      return res;
+    };
+  }
+
+  /**
+   * combinator or.
+   * @param andFinder finder to combine
+   * @return new finder including previous finders
+   */
+  default Finder and(Finder andFinder) {
+    return
+        txt -> this
+            .find(txt)
+            .stream()
+            .flatMap(line -> andFinder.find(line).stream())
+            .collect(Collectors.toList());
+  }
+
+}

combinator/src/main/java/com/iluwatar/combinator/Finders.java

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+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.combinator;
+
+import java.util.ArrayList;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * Complex finders consisting of simple finder.
+ */
+public class Finders {
+  private Finders() {
+  }
+
+
+  /**
+   * Finder to find a complex query.
+   * @param query to find
+   * @param orQuery alternative to find
+   * @param notQuery exclude from search
+   * @return new finder
+   */
+  public static Finder advancedFinder(String query, String orQuery, String notQuery) {
+    return
+        Finder.contains(query)
+            .or(Finder.contains(orQuery))
+            .not(Finder.contains(notQuery));
+  }
+
+  /**
+   * Filtered finder looking a query with excluded queries as well.
+   * @param query to find
+   * @param excludeQueries to exclude
+   * @return new finder
+   */
+  public static Finder filteredFinder(String query, String... excludeQueries) {
+    var finder = Finder.contains(query);
+
+    for (String q : excludeQueries) {
+      finder = finder.not(Finder.contains(q));
+    }
+    return finder;
+
+  }
+
+  /**
+   * Specialized query. Every next query is looked in previous result.
+   * @param queries array with queries
+   * @return new finder
+   */
+  public static Finder specializedFinder(String... queries) {
+    var finder = identMult();
+
+    for (String query : queries) {
+      finder = finder.and(Finder.contains(query));
+    }
+    return finder;
+  }
+
+  /**
+   * Expanded query. Looking for alternatives.
+   * @param queries array with queries.
+   * @return new finder
+   */
+  public static Finder expandedFinder(String... queries) {
+    var finder = identSum();
+
+    for (String query : queries) {
+      finder = finder.or(Finder.contains(query));
+    }
+    return finder;
+  }
+
+  private static Finder identMult() {
+    return txt -> Stream.of(txt.split("\n")).collect(Collectors.toList());
+  }
+
+  private static Finder identSum() {
+    return txt -> new ArrayList<>();
+  }
+}