org.jparsec.examples.calculator.Calculator Maven / Gradle / Ivy

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 * Copyright (C) jparsec.org                                                *
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package org.jparsec.examples.calculator;

import static org.jparsec.Scanners.isChar;

import java.util.function.BinaryOperator;
import java.util.function.UnaryOperator;

import org.jparsec.OperatorTable;
import org.jparsec.Parser;
import org.jparsec.Scanners;

/**
 * The main calculator parser.
 * 
 * @author Ben Yu
 */
public final class Calculator {
  
  /** Parsers {@code source} and evaluates to an {@link Integer}. */
  public static int evaluate(String source) {
    return parser().parse(source);
  }
  
  static final Parser NUMBER = Scanners.INTEGER.map(Integer::valueOf);
  
  static final BinaryOperator PLUS = (a, b) -> a + b;
  
  static final BinaryOperator MINUS = (a, b) -> a - b;
  
  static final BinaryOperator MUL = (a, b) -> a * b;
  
  static final BinaryOperator DIV = (a, b) -> a / b;
  
  static final BinaryOperator MOD = (a, b) -> a % b;
  
  static final UnaryOperator NEG = a -> -a;
  
  private static  Parser op(char ch, T value) {
    return isChar(ch).retn(value);
  }
  
  static Parser parser() {
    Parser.Reference ref = Parser.newReference();
    Parser term = ref.lazy().between(isChar('('), isChar(')')).or(NUMBER);
    Parser parser = new OperatorTable()
        .prefix(op('-', NEG), 100)
        .infixl(op('+', PLUS), 10)
        .infixl(op('-', MINUS), 10)
        .infixl(op('*', MUL), 20)
        .infixl(op('/', DIV), 20)
        .infixl(op('%', MOD), 20)
        .build(term);
    ref.set(parser);
    return parser;
  }
}