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Pattern combinator (iluwatar#1105)
* init * add pattern
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‎combinator/README.md

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

‎combinator/pom.xml

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

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

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

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

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

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

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

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