[antlr-interest] tree grammar

[Anders Karlsson]

Hi again,

I should have specified a subject, sorry about forgetting that.

I also forgot to mention the version i use ANTLRWorks 1.1.7 and ANTLR 3.0.1

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I was trying to create a tree parser but when I write

tree grammar xxx;

at the top of the file (or lex grammar xxx for that matter)

I get a null pointer exception as follows:

Cannot generate the grammar because:
error(10): internal error: C:....path to my xxx.g file : java.lang.NullPointerException
org.antlr.tool.GrammarSanity.traceStatesLookingForLeftRecursion(GrammarSanity.java:105)
...
java.lang.Thread.run(Unknown Source)

Any ideas what I am doing wrong?

The grammar follows (from the ANTLR3 ref book,slightly modified):

tree grammar evaluate;       // this causes the error, if I remove tree there is no exception

options {
tokenVocab=expeval; // read tokens from this file expeval.tokens
ASTLabelType=CommonTree;
language=C;
}

@header {
  #include <stdio.h> // here some using/includes could be specified.
}

@members {
  // here some instance variables could be defined.
}

prog
: statement+;

statement
:   expr { char m[32]; puts( itoa( $expr.value, m, 10 ) ); }
;

expr returns [int value]
: ^('+' a=expr b=expr) { $value=a+b; }
| ^('-' a=expr b=expr) { $value=a-b; }
| ^('*' a=expr b=expr) { $value=a*b; }
| ^('/' a=expr b=expr) { $value=a/b; }
| INT { $value=atoi((const char*)($INT.text->chars)); }
;

INT
:   '0'..'9'+
;

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