1 files changed, 58 insertions, 0 deletions
diff --git a/antlr-3.4/runtime/Ruby/lib/antlr3/modes/filter.rb b/antlr-3.4/runtime/Ruby/lib/antlr3/modes/filter.rb
new file mode 100644
index 0000000..70b63bf
--- /dev/null
+++ b/antlr-3.4/runtime/Ruby/lib/antlr3/modes/filter.rb
@@ -0,0 +1,58 @@
+#!/usr/bin/ruby
+# encoding: utf-8
+
+require 'antlr3'
+
+module ANTLR3
+=begin rdoc ANTLR3::FilterMode
+
+If a lexer grammar specifies the <tt>filter = true</t> option, the generated
+Lexer code will include this module. It modifies the standard
+<tt>next_token</tt> to catch RecognitionErrors and skip ahead in the input until
+the token! method can match a token without raising a RecognitionError.
+
+See http://www.antlr.org/wiki/display/ANTLR3/Lexical+filters for more info on
+lexer filter mode.
+
+=end
+module FilterMode
+  def next_token
+    # if at end-of-file, return the EOF token
+    @input.peek == ANTLR3::EOF and return ANTLR3::EOF_TOKEN
+    
+    @state.token                = nil
+    @state.channel              = ANTLR3::DEFAULT_CHANNEL
+    @state.token_start_position = @input.index
+    @state.token_start_column   = @input.column
+    @state.token_start_line     = @input.line
+    @state.text                 = nil
+    @state.backtracking         = 1
+    
+    m = @input.mark
+    token!
+    @input.release( m )
+    emit
+    return @state.token
+  rescue ANTLR3::BacktrackingFailed
+    # token! backtracks with synpred at backtracking==2
+    # and we set the synpredgate to allow actions at level 1.
+    @input.rewind( m )
+    @input.consume # advance one char and try again
+    retry
+  rescue ANTLR3::Error::RecognitionError => re
+    # shouldn't happen in backtracking mode, but...
+    report_error( re )
+    recover( re )
+  ensure
+    @state.backtracking = 0
+  end
+  
+  def memoize( rule, start_index, success )
+    super( rule, start_index, success ) if @state.backtracking > 1
+  end
+  
+  def already_parsed_rule?( rule )
+    @state.backtracking > 1 ? super( rule ) : false
+  end
+end
+end