filter.rb revision 324c4644fee44b9898524c09511bd33c3f12e2df 
1#!/usr/bin/ruby
2# encoding: utf-8
3
4require 'antlr3'
5
6module ANTLR3
7=begin rdoc ANTLR3::FilterMode
8
9If a lexer grammar specifies the <tt>filter = true</t> option, the generated
10Lexer code will include this module. It modifies the standard
11<tt>next_token</tt> to catch RecognitionErrors and skip ahead in the input until
12the token! method can match a token without raising a RecognitionError.
13
14See http://www.antlr.org/wiki/display/ANTLR3/Lexical+filters for more info on
15lexer filter mode.
16
17=end
18module FilterMode
19  def next_token
20    # if at end-of-file, return the EOF token
21    @input.peek == ANTLR3::EOF and return ANTLR3::EOF_TOKEN
22    
23    @state.token                = nil
24    @state.channel              = ANTLR3::DEFAULT_CHANNEL
25    @state.token_start_position = @input.index
26    @state.token_start_column   = @input.column
27    @state.token_start_line     = @input.line
28    @state.text                 = nil
29    @state.backtracking         = 1
30    
31    m = @input.mark
32    token!
33    @input.release( m )
34    emit
35    return @state.token
36  rescue ANTLR3::BacktrackingFailed
37    # token! backtracks with synpred at backtracking==2
38    # and we set the synpredgate to allow actions at level 1.
39    @input.rewind( m )
40    @input.consume # advance one char and try again
41    retry
42  rescue ANTLR3::Error::RecognitionError => re
43    # shouldn't happen in backtracking mode, but...
44    report_error( re )
45    recover( re )
46  ensure
47    @state.backtracking = 0
48  end
49  
50  def memoize( rule, start_index, success )
51    super( rule, start_index, success ) if @state.backtracking > 1
52  end
53  
54  def already_parsed_rule?( rule )
55    @state.backtracking > 1 ? super( rule ) : false
56  end
57end
58end
59