From dcb00b4fe814f550b2463e2babe91de8980f5997 Mon Sep 17 00:00:00 2001
From: Jeremy Ashkenas <jashkenas@gmail.com>
Date: Mon, 8 Mar 2010 22:48:14 -0500
Subject: [PATCH] minor refactors to balanced_string

---
 lib/lexer.js     | 47 +++++++++++++++++++++++------------------------
 src/lexer.coffee | 34 +++++++++++++++++-----------------
 2 files changed, 40 insertions(+), 41 deletions(-)

diff --git a/lib/lexer.js b/lib/lexer.js
index b80d471a..9a6dc514 100644
--- a/lib/lexer.js
+++ b/lib/lexer.js
@@ -169,7 +169,8 @@
     };
     // Matches regular expression literals. Lexing regular expressions is difficult
     // to distinguish from division, so we borrow some basic heuristics from
-    // JavaScript and Ruby.
+    // JavaScript and Ruby, borrow slash balancing from `@balanced_token`, and
+    // borrow interpolation from `@interpolate_string`.
     Lexer.prototype.regex_token = function regex_token() {
       var flags, regex, str;
       if (!(this.chunk.match(REGEX_START))) {
@@ -412,26 +413,27 @@
       levels = [];
       i = 0;
       while (i < str.length) {
-        _a = delimited;
-        for (_b = 0, _c = _a.length; _b < _c; _b++) {
-          pair = _a[_b];
-          _d = pair;
-          open = _d[0];
-          close = _d[1];
-          if (levels.length && starts(str, '\\', i)) {
-            i += 1;
-            break;
-          } else if (levels.length && starts(str, close, i) && levels[levels.length - 1] === pair) {
-            levels.pop();
-            i += close.length - 1;
-            if (!(levels.length)) {
-              i += 1;
+        if (levels.length && starts(str, '\\', i)) {
+          i += 1;
+        } else {
+          _a = delimited;
+          for (_b = 0, _c = _a.length; _b < _c; _b++) {
+            pair = _a[_b];
+            _d = pair;
+            open = _d[0];
+            close = _d[1];
+            if (levels.length && starts(str, close, i) && levels[levels.length - 1] === pair) {
+              levels.pop();
+              i += close.length - 1;
+              if (!(levels.length)) {
+                i += 1;
+              }
+              break;
+            } else if (starts(str, open, i)) {
+              levels.push(pair);
+              i += open.length - 1;
+              break;
             }
-            break;
-          } else if (starts(str, open, i)) {
-            levels.push(pair);
-            i += open.length - 1;
-            break;
           }
         }
         if (!levels.length || slash && starts(str, '\n', i)) {
@@ -445,10 +447,7 @@
         }
         throw new Error("SyntaxError: Unterminated " + (levels.pop()[0]) + " starting on line " + (this.line + 1));
       }
-      if (i === 0) {
-        return false;
-      }
-      return str.substring(0, i);
+      return !i ? false : str.substring(0, i);
     };
     // Expand variables and expressions inside double-quoted strings using
     // [ECMA Harmony's interpolation syntax](http://wiki.ecmascript.org/doku.php?id=strawman:string_interpolation)
diff --git a/src/lexer.coffee b/src/lexer.coffee
index c2908e43..fd532159 100644
--- a/src/lexer.coffee
+++ b/src/lexer.coffee
@@ -124,7 +124,8 @@ exports.Lexer: class Lexer
 
   # Matches regular expression literals. Lexing regular expressions is difficult
   # to distinguish from division, so we borrow some basic heuristics from
-  # JavaScript and Ruby.
+  # JavaScript and Ruby, borrow slash balancing from `@balanced_token`, and
+  # borrow interpolation from `@interpolate_string`.
   regex_token: ->
     return false unless @chunk.match REGEX_START
     return false if     include NOT_REGEX, @tag()
@@ -311,27 +312,26 @@ exports.Lexer: class Lexer
     levels: []
     i: 0
     while i < str.length
-      for pair in delimited
-        [open, close]: pair
-        if levels.length and starts str, '\\', i
-          i += 1
-          break
-        else if levels.length and starts(str, close, i) and levels[levels.length - 1] is pair
-          levels.pop()
-          i += close.length - 1
-          i += 1 unless levels.length
-          break
-        else if starts str, open, i
-          levels.push(pair)
-          i += open.length - 1
-          break
+      if levels.length and starts str, '\\', i
+        i += 1
+      else
+        for pair in delimited
+          [open, close]: pair
+          if levels.length and starts(str, close, i) and levels[levels.length - 1] is pair
+            levels.pop()
+            i += close.length - 1
+            i += 1 unless levels.length
+            break
+          else if starts str, open, i
+            levels.push(pair)
+            i += open.length - 1
+            break
       break if not levels.length or slash and starts str, '\n', i
       i += 1
     if levels.length
       return false if slash
       throw new Error "SyntaxError: Unterminated ${levels.pop()[0]} starting on line ${@line + 1}"
-    return false if i is 0
-    return str.substring(0, i)
+    if not i then false else str.substring(0, i)
 
   # Expand variables and expressions inside double-quoted strings using
   # [ECMA Harmony's interpolation syntax](http://wiki.ecmascript.org/doku.php?id=strawman:string_interpolation)