[antlr-interest] How to tell assignment from equal?

[Miguel Ping]

Hi,

You can use a predicate to check for an '=' after the first '=' and
then change the token type:


ASSIGN : '=' ('=' {$type = COMPARE;} ) ? ;

the ('=') ? rule checks for existence of the '=' in the ASSIGN token,
after reading the first '='. The action {$type = COMPARE;} sets the
token type >only< if the predicate is true, that is only if the lexer
found a '=' after the first '='.

Hope it helps,
Miguel Ping

On 5/2/07, me 262 <me262c at gmail.com> wrote:
> Hi,
>
>   I am having problem with equal "==" and assign "=" in my grammar file.
>
> .......
> 	ASSIGN		: '='	;
> .......
> 			
> 	COMPARE :
> 			( '<'
> 			| "<="
> 			| '>'
> 			| ">="
> 			| "=="
> 			| "!="
> 			);
>
> I get message:
>
> my.g: warning:lexical nondeterminism between rules ASSIGN and COMPARE upon
> script.g:     k==1:'='
> script.g:     k==2:<end-of-token>
>
> It must be a very common problem.
> Thanks in advance!
>