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'use strict';
// --------------------------------------------------------------------// Imports// --------------------------------------------------------------------
const common = require('./common');const pexprs = require('./pexprs-main');
// --------------------------------------------------------------------// Operations// --------------------------------------------------------------------
// Returns `true` if this parsing expression may accept without consuming any input.pexprs.PExpr.prototype.isNullable = function(grammar) {  return this._isNullable(grammar, Object.create(null));};
pexprs.PExpr.prototype._isNullable = common.abstract('_isNullable');
pexprs.any._isNullable =  pexprs.Range.prototype._isNullable =  pexprs.Param.prototype._isNullable =  pexprs.Plus.prototype._isNullable =  pexprs.UnicodeChar.prototype._isNullable =    function(grammar, memo) {      return false;    };
pexprs.end._isNullable = function(grammar, memo) {  return true;};
pexprs.Terminal.prototype._isNullable = function(grammar, memo) {  if (typeof this.obj === 'string') {    // This is an over-simplification: it's only correct if the input is a string. If it's an array    // or an object, then the empty string parsing expression is not nullable.    return this.obj === '';  } else {    return false;  }};
pexprs.Alt.prototype._isNullable = function(grammar, memo) {  return this.terms.length === 0 || this.terms.some(term => term._isNullable(grammar, memo));};
pexprs.Seq.prototype._isNullable = function(grammar, memo) {  return this.factors.every(factor => factor._isNullable(grammar, memo));};
pexprs.Star.prototype._isNullable =  pexprs.Opt.prototype._isNullable =  pexprs.Not.prototype._isNullable =  pexprs.Lookahead.prototype._isNullable =    function(grammar, memo) {      return true;    };
pexprs.Lex.prototype._isNullable = function(grammar, memo) {  return this.expr._isNullable(grammar, memo);};
pexprs.Apply.prototype._isNullable = function(grammar, memo) {  const key = this.toMemoKey();  if (!Object.prototype.hasOwnProperty.call(memo, key)) {    const {body} = grammar.rules[this.ruleName];    const inlined = body.substituteParams(this.args);    memo[key] = false; // Prevent infinite recursion for recursive rules.    memo[key] = inlined._isNullable(grammar, memo);  }  return memo[key];};