[antlr-interest] Trying to get started with ANTLR; two problems

[Niemeijer, R.A.]

Hello everyone,

 

I'm trying to get started with ANTLR but I'm having two slight problems.
I'm undoubtedly doing something wrong but I can't figure out what.

 

Let's start with the program code:

 

static void Main(string[] args)

{

    var input = new ANTLRStringStream("2*3=1+5");

    var lexer = new TestLexer(input);

    var tokens = new CommonTokenStream(lexer);

 

    var parser = new TestParser(tokens);

    var tree = parser.stat().Tree as CommonTree;

 

    Console.WriteLine(tree.ToStringTree());

 

    var val = parser.stat().val;

    Console.WriteLine(val);

}

 

Nothing too complex. First I create the tree and print it, then I print
the evaluated result.

 

The generated output:

(= (* 2 3) (+ 1 5))

line 0:-1 no viable alternative at input '<EOF>'

False

 

The tree generation and printing goes without a hitch, but the
evaluation gives an error message and the wrong result. Time for the
grammar code:

 

grammar Test;

 

options

{

 language = CSharp;

 output = AST;

}

 

// LEXER --------------------------------------

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

PLUS    :    '+';

MINUS    :    '-';

TIMES    :    '*';

DIV    :    '/';

EQ    :    '=';

 

// PARSER--------------------------------------

stat returns [bool val]

    :    a=exprL3 EOF!

         { $val = $a.val; }

    ;

exprL3 returns [bool val]

    :    a=exprL2 EQ^ b=exprL2

         { $val = true; }

    ;

exprL2 returns [int result]

    :    a=exprL1

         (

          (TIMES^ b=exprL1)

          |

          (DIV^ b=exprL1)

         )*

    ;

 

exprL1 returns [int result]

    :    a=atom

         (

          (PLUS^ b=atom)

          |

          (MINUS^ b=atom)

         )*

    ;

atom returns [int result]

    :    a=INT

    |    '(' exprL2 ')'

    ;

 

Since I have defined stat as "exprL3 EOF!", which seems to be the common
method in the examples I could find, I don't quite understand why it's
complaining about the lack of a viable alternative.

As for the evaluation value: if I change stat to say "$val = true" it
indeed returns true. If however I defer this to exprL3 it doesn't work
anymore.

 

Can anyone tell me what I'm doing wrong?

Thanks in advance.

 

Regards,

                 R.A. Niemeijer

 

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