From 3548861b314df7e119fd8d60b1b714b00b76a24a Mon Sep 17 00:00:00 2001
From: Zachary Carter <zack.carter@gmail.com>
Date: Mon, 31 Mar 2014 06:40:11 -0700
Subject: [PATCH] create a new instance of the lexer on each parse

---
 lib/jison.js | 45 +++++++++++++++++++++++----------------------
 1 file changed, 23 insertions(+), 22 deletions(-)

diff --git a/lib/jison.js b/lib/jison.js
index 798b23dfd..de3212afb 100755
--- a/lib/jison.js
+++ b/lib/jison.js
@@ -1219,17 +1219,18 @@ parser.parse = function parse (input) {
 
     //this.reductionCount = this.shiftCount = 0;
 
-    this.lexer.setInput(input);
-    this.lexer.yy = this.yy;
-    this.yy.lexer = this.lexer;
+    var lexer = Object.create(this.lexer);
+
+    lexer.setInput(input, this.yy);
+    this.yy.lexer = lexer;
     this.yy.parser = this;
-    if (typeof this.lexer.yylloc == 'undefined') {
-        this.lexer.yylloc = {};
+    if (typeof lexer.yylloc == 'undefined') {
+        lexer.yylloc = {};
     }
-    var yyloc = this.lexer.yylloc;
+    var yyloc = lexer.yylloc;
     lstack.push(yyloc);
 
-    var ranges = this.lexer.options && this.lexer.options.ranges;
+    var ranges = lexer.options && lexer.options.ranges;
 
     if (typeof this.yy.parseError === 'function') {
         this.parseError = this.yy.parseError;
@@ -1245,7 +1246,7 @@ parser.parse = function parse (input) {
 
     function lex() {
         var token;
-        token = self.lexer.lex() || EOF; // $end = 1
+        token = lexer.lex() || EOF; // $end = 1
         // if token isn't its numeric value, convert
         if (typeof token !== 'number') {
             token = self.symbols_[token] || token;
@@ -1307,17 +1308,17 @@ _handle_error:
                         expected.push("'"+this.terminals_[p]+"'");
                     }
                 }
-                if (this.lexer.showPosition) {
-                    errStr = 'Parse error on line '+(yylineno+1)+":\n"+this.lexer.showPosition()+"\nExpecting "+expected.join(', ') + ", got '" + (this.terminals_[symbol] || symbol)+ "'";
+                if (lexer.showPosition) {
+                    errStr = 'Parse error on line '+(yylineno+1)+":\n"+lexer.showPosition()+"\nExpecting "+expected.join(', ') + ", got '" + (this.terminals_[symbol] || symbol)+ "'";
                 } else {
                     errStr = 'Parse error on line '+(yylineno+1)+": Unexpected " +
                                   (symbol == EOF ? "end of input" :
                                               ("'"+(this.terminals_[symbol] || symbol)+"'"));
                 }
                 this.parseError(errStr, {
-                    text: this.lexer.match,
+                    text: lexer.match,
                     token: this.terminals_[symbol] || symbol,
-                    line: this.lexer.yylineno,
+                    line: lexer.yylineno,
                     loc: yyloc,
                     expected: expected,
                     recoverable: (error_rule_depth !== false)
@@ -1333,10 +1334,10 @@ _handle_error:
                 }
 
                 // discard current lookahead and grab another
-                yyleng = this.lexer.yyleng;
-                yytext = this.lexer.yytext;
-                yylineno = this.lexer.yylineno;
-                yyloc = this.lexer.yylloc;
+                yyleng = lexer.yyleng;
+                yytext = lexer.yytext;
+                yylineno = lexer.yylineno;
+                yyloc = lexer.yylloc;
                 symbol = lex();
             }
 
@@ -1363,15 +1364,15 @@ _handle_error:
                 //this.shiftCount++;
 
                 stack.push(symbol);
-                vstack.push(this.lexer.yytext);
-                lstack.push(this.lexer.yylloc);
+                vstack.push(lexer.yytext);
+                lstack.push(lexer.yylloc);
                 stack.push(action[1]); // push state
                 symbol = null;
                 if (!preErrorSymbol) { // normal execution/no error
-                    yyleng = this.lexer.yyleng;
-                    yytext = this.lexer.yytext;
-                    yylineno = this.lexer.yylineno;
-                    yyloc = this.lexer.yylloc;
+                    yyleng = lexer.yyleng;
+                    yytext = lexer.yytext;
+                    yylineno = lexer.yylineno;
+                    yyloc = lexer.yylloc;
                     if (recovering > 0) {
                         recovering--;
                     }