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It is a handwritten prolog parser, it allows to parse prolog sources written in Edinburgh Prolog style

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/*
 * Copyright (c) 2011-2018 Igor Maznitsa. All rights reserved.
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package com.igormaznitsa.prologparser.tokenizer;

import java.util.List;
import java.util.Optional;

/**
 * Associativity of Prolog operators.
 */
@SuppressWarnings("unused")
public enum OpAssoc {

  /**
   * Postfix, non-associative.
   */
  XF("xf", 1),
  /**
   * Postfix, associative.
   */
  YF("yf", 1),
  /**
   * Prefix, non-associative.
   */
  FX("fx", 1),
  /**
   * Prefix, associative.
   */
  FY("fy", 1),
  /**
   * Infix, non-associative.
   */
  XFX("xfx", 2),
  /**
   * Infix, right-associative.
   */
  XFY("xfy", 2),
  /**
   * Infix, left-associative.
   */
  YFX("yfx", 2);

  public static final List VALUES = List.of(OpAssoc.values());
  private final String text;
  private final int arity;

  OpAssoc(final String text, final int arity) {
    this.text = text;
    this.arity = arity;
  }

  public static Optional findForName(final String str) {
    return VALUES.stream().filter(x -> x.text.equals(str)).findFirst();
  }

  public boolean isPostfix() {
    return this == XF || this == YF;
  }

  public boolean isPrefix() {
    return this == FX || this == FY;
  }

  public int getArity() {
    return this.arity;
  }

  public String getText() {
    return text;
  }
}