HowToOverrideLexerImpl


1   package fri.patterns.interpreter.parsergenerator.examples;
2   
3   import java.util.List  ;
4   import java.util.Map  ;
5   import fri.patterns.interpreter.parsergenerator.Lexer;
6   import fri.patterns.interpreter.parsergenerator.Parser;
7   import fri.patterns.interpreter.parsergenerator.Token;
8   import fri.patterns.interpreter.parsergenerator.builder.SerializedLexer;
9   import fri.patterns.interpreter.parsergenerator.builder.SerializedParser;
10  import fri.patterns.interpreter.parsergenerator.lexer.LexerBuilder;
11  import fri.patterns.interpreter.parsergenerator.lexer.LexerException;
12  import fri.patterns.interpreter.parsergenerator.lexer.LexerImpl;
13  import fri.patterns.interpreter.parsergenerator.lexer.Strategy;
14  import fri.patterns.interpreter.parsergenerator.syntax.Syntax;
15  import fri.patterns.interpreter.parsergenerator.syntax.SyntaxException;
16  
17  /**
18   * This sample shows how to set another Lexer implementation
19   * into the Parser-builder.
20   * 
21   * @author Fritz Ritzberger
22   */
23  public class HowToOverrideLexerImpl {
24      public static void main(String   args[])
25          throws Exception  
26      {
27          // a Lexer derivate class that prints a message
28          class OverrideLexer extends LexerImpl
29          {
30              public OverrideLexer(List   ignoredSymbols, Map   charConsumers)    {
31                  super(ignoredSymbols, charConsumers);
32              }
33              /** Could provide another lexing Strategy. */
34              public Strategy newStrategy()   {
35                  return super.newStrategy();
36              }
37          };
38  
39          // override the Parser builder to install the new Lexer implementation
40          SerializedParser builder = new SerializedParser()   {
41              protected SerializedLexer newSerializedLexer()  // override SerializedLexer factory method
42                  throws Exception  
43              {
44                  return new SerializedLexer()    {
45                      protected LexerBuilder newLexerBuilder(Syntax syntax, List   ignoredSymbols)  // override LexerBuilder factory method
46                          throws LexerException, SyntaxException
47                      {
48                          return new LexerBuilder(syntax, ignoredSymbols) {
49                              public Lexer getLexer() {   // override Lexer factory method
50                                  return new OverrideLexer(ignoredSymbols, charConsumers);
51                              }
52                          };
53                      }
54                  };
55              }
56          };
57          
58          String   [][] syntaxInput = {
59              { "Start", "\"Hello\"", "\"World\"" },
60              { Token.IGNORED, "`whitespaces`" },
61          };
62          
63          Parser parser = builder.get(syntaxInput);
64          boolean ok = parser.parse("Hello World");
65          System.err.println("Parsing was "+ok);
66      }
67  
68  }
69
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