merged stan's interpolation_3, a couple of tweaks

lib/lexer.js

@@ -33,7 +33,7 @@
     Lexer.prototype.tokenize = function tokenize(code, options) {
       var o;
       o = options || {};
-      this.code = code;
+      this.code = code || '';
       // The remainder of the source code.
       this.i = 0;
       // Current character position we're parsing.
@@ -176,6 +176,9 @@
     // JavaScript and Ruby.
     Lexer.prototype.regex_token = function regex_token() {
       var _a, _b, _c, _d, _e, each, flags, i, index, interp_tokens, merge, regex, str, supress;
+      if (!(starts(this.chunk, '/'))) {
+        return false;
+      }
       if (!((regex = this.balanced_token((supress = true), ['/', '/'])))) {
         return false;
       }

lib/rewriter.js

@@ -81,7 +81,7 @@
     Rewriter.prototype.remove_leading_newlines = function remove_leading_newlines() {
       var _a;
       _a = [];
-      while (this.tokens[0][0] === 'TERMINATOR') {
+      while (this.tokens[0] && this.tokens[0][0] === 'TERMINATOR') {
         _a.push(this.tokens.shift());
       }
       return _a;

src/lexer.coffee

@@ -36,7 +36,7 @@ exports.Lexer: class Lexer
   # unless explicitly asked not to.
   tokenize: (code, options) ->
     o        : options or {}
-    @code    : code         # The remainder of the source code.
+    @code    : code or ''   # The remainder of the source code.
     @i       : 0            # Current character position we're parsing.
     @line    : o.line or 0  # The current line.
     @indent  : 0            # The current indentation level.
@@ -126,6 +126,7 @@ exports.Lexer: class Lexer
   # to distinguish from division, so we borrow some basic heuristics from
   # JavaScript and Ruby.
   regex_token: ->
+    return false unless starts @chunk, '/'
     return false unless regex: @balanced_token supress: true, ['/', '/']
     return false if regex.length < 3 or regex.match /^\/\s+|\n/
     return false if include NOT_REGEX, @tag()

src/rewriter.coffee

@@ -62,7 +62,7 @@ exports.Rewriter: class Rewriter
   # Leading newlines would introduce an ambiguity in the grammar, so we
   # dispatch them here.
   remove_leading_newlines: ->
-    @tokens.shift() while @tokens[0][0] is 'TERMINATOR'
+    @tokens.shift() while @tokens[0] and @tokens[0][0] is 'TERMINATOR'
 
   # Some blocks occur in the middle of expressions -- when we're expecting
   # this, remove their trailing newlines.