forked from jasder/antlr
80 lines
2.9 KiB
Markdown
80 lines
2.9 KiB
Markdown
# Parser and lexer interpreters
|
|
|
|
*Since ANTLR 4.2*
|
|
|
|
For small parsing tasks it is sometimes convenient to use ANTLR in interpreted mode, rather than generating a parser in a particular target, compiling it and running it as part of your application. Here's some sample code that creates lexer and parser Grammar objects and then creates interpreters. Once we have a ParserInterpreter, we can use it to parse starting in any rule we like, given a rule index (which the Grammar can provide).
|
|
|
|
```java
|
|
LexerGrammar lg = new LexerGrammar(
|
|
"lexer grammar L;\n" +
|
|
"A : 'a' ;\n" +
|
|
"B : 'b' ;\n" +
|
|
"C : 'c' ;\n");
|
|
Grammar g = new Grammar(
|
|
"parser grammar T;\n" +
|
|
"s : (A|B)* C ;\n",
|
|
lg);
|
|
LexerInterpreter lexEngine =
|
|
lg.createLexerInterpreter(new ANTLRInputStream(input));
|
|
CommonTokenStream tokens = new CommonTokenStream(lexEngine);
|
|
ParserInterpreter parser = g.createParserInterpreter(tokens);
|
|
ParseTree t = parser.parse(g.rules.get(startRule).index);
|
|
```
|
|
|
|
You can also load combined grammars from a file:
|
|
|
|
```java
|
|
public static ParseTree parse(String fileName,
|
|
String combinedGrammarFileName,
|
|
String startRule)
|
|
throws IOException
|
|
{
|
|
final Grammar g = Grammar.load(combinedGrammarFileName);
|
|
LexerInterpreter lexEngine = g.createLexerInterpreter(new ANTLRFileStream(fileName));
|
|
CommonTokenStream tokens = new CommonTokenStream(lexEngine);
|
|
ParserInterpreter parser = g.createParserInterpreter(tokens);
|
|
ParseTree t = parser.parse(g.getRule(startRule).index);
|
|
System.out.println("parse tree: "+t.toStringTree(parser));
|
|
return t;
|
|
}
|
|
```
|
|
|
|
Then:
|
|
|
|
```java
|
|
ParseTree t = parse("T.om",
|
|
MantraGrammar,
|
|
"compilationUnit");
|
|
```
|
|
|
|
To load separate lexer/parser grammars, do this:
|
|
|
|
```java
|
|
public static ParseTree parse(String fileNameToParse,
|
|
String lexerGrammarFileName,
|
|
String parserGrammarFileName,
|
|
String startRule)
|
|
throws IOException
|
|
{
|
|
final LexerGrammar lg = (LexerGrammar) Grammar.load(lexerGrammarFileName);
|
|
final Grammar pg = Grammar.load(parserGrammarFileName, lg);
|
|
ANTLRFileStream input = new ANTLRFileStream(fileNameToParse);
|
|
LexerInterpreter lexEngine = lg.createLexerInterpreter(input);
|
|
CommonTokenStream tokens = new CommonTokenStream(lexEngine);
|
|
ParserInterpreter parser = pg.createParserInterpreter(tokens);
|
|
ParseTree t = parser.parse(pg.getRule(startRule).index);
|
|
System.out.println("parse tree: " + t.toStringTree(parser));
|
|
return t;
|
|
}
|
|
```
|
|
|
|
Then:
|
|
|
|
```java
|
|
ParseTree t = parse(fileName, XMLLexerGrammar, XMLParserGrammar, "document");
|
|
```
|
|
|
|
This is also how we will integrate instantaneous parsing into ANTLRWorks2 and development environment plug-ins.
|
|
|
|
See [TestParserInterpreter.java](https://github.com/antlr/antlr4/blob/master/tool-testsuite/test/org/antlr/v4/test/tool/TestParserInterpreter.java).
|