CODEWITHSUNDEEP
parsingantlr4abstract-syntax-treelexer
user3868051
user3868051

Reputation: 1259

antlr 4.7 error while ast generation

I am trying to run strp by step instruction as per - http://meri-stuff.blogspot.com/2011/08/antlr-tutorial-hello-word.html

Original code as per the above webpage - 

public CommonTree compile(String expression) {
try {
  //lexer splits input into tokens
  ANTLRStringStream input = new ANTLRStringStream(expression);
  TokenStream tokens = new CommonTokenStream( new S001HelloWordLexer( input ) );

  //parser generates abstract syntax tree
  S001HelloWordParser parser = new S001HelloWordParser(tokens);
  S001HelloWordParser.expression_return ret = parser.expression();

  //acquire parse result
  CommonTree ast = (CommonTree) ret.tree;
  printTree(ast);
  return ast;
} catch (RecognitionException e) {
  throw new IllegalStateException("Recognition exception is never thrown, only declared.");
}
}

I have modified some part of the code below: 

public CommonTree compile(String expression) {
    try {
      //lexer splits input into tokens
      ANTLRStringStream input = new ANTLRStringStream(expression);
      TokenStream tokens = new CommonTokenStream( (TokenSource) new S001HelloWordLexer( (CharStream) input ) );

      //parser generates abstract syntax tree
      S001HelloWordParser parser = new S001HelloWordParser((org.antlr.v4.runtime.TokenStream) tokens);
      S001HelloWordParser.expression_return ret = parser.expression();

      //acquire parse result
      CommonTree ast = (CommonTree) ret.tree;
      printTree(ast);
      return ast;
    } catch (RecognitionException e) {
      throw new IllegalStateException("Recognition exception is never thrown, only declared.");
  }
}

The issue is in my S001HelloWordParser file, there is no method as expression() nor is there a static class names 'expression_return', so I am not able to create the variable 'ret' on whom I could call the tree() method. Is there anything I am missing here?

How else can I generate the tree? Or any idea about the process using antlr 4.7 version?

Please help. Thanks!

Upvotes: 0

Views: 906

Answers (1)

Bart Kiers
Bart Kiers

Reputation: 170308

I am trying to run strp by step instruction as per - http://meri-stuff.blogspot.com/2011/08/antlr-tutorial-hello-word.html

Don't. That tutorial is about ANTLR 3, you need to find an ANTLR 4 tutorial.

The issue is in my S001HelloWordParser file, there is no method as expression() nor is there a static class names 'expression_return'

That means your S001HelloWord grammar does not contain a parser rule called expression.

Start from the source: https://github.com/antlr/antlr4/blob/master/doc/getting-started.md

And here's a Q&A (with full code examples) about an expression parser for ANTLR4: If/else statements in ANTLR using listeners

Upvotes: 1

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