pegjs/lib/compiler/asts.js

"use strict";

let visitor = require("./visitor");

// AST utilities.
let asts = {
  findRule: function(ast, name) {
    for (let i = 0; i < ast.rules.length; i++) {
      if (ast.rules[i].name === name) {
        return ast.rules[i];
      }
    }

    return undefined;
  },

  indexOfRule: function(ast, name) {
    for (let i = 0; i < ast.rules.length; i++) {
      if (ast.rules[i].name === name) {
        return i;
      }
    }

    return -1;
  },

  alwaysConsumesOnSuccess: function(ast, node) {
    function consumesTrue()  { return true;  }
    function consumesFalse() { return false; }

    function consumesExpression(node) {
      return consumes(node.expression);
    }

    let consumes = visitor.build({
      rule:  consumesExpression,
      named: consumesExpression,

      choice: function(node) {
        return node.alternatives.every(consumes);
      },

      action: consumesExpression,

      sequence: function(node) {
        return node.elements.some(consumes);
      },

      labeled:      consumesExpression,
      text:         consumesExpression,
      simple_and:   consumesFalse,
      simple_not:   consumesFalse,
      optional:     consumesFalse,
      zero_or_more: consumesFalse,
      one_or_more:  consumesExpression,
      group:        consumesExpression,
      semantic_and: consumesFalse,
      semantic_not: consumesFalse,

      rule_ref: function(node) {
        return consumes(asts.findRule(ast, node.name));
      },

      literal: function(node) {
        return node.value !== "";
      },

      "class": consumesTrue,
      any:     consumesTrue
    });

    return consumes(node);
  }
};

module.exports = asts;