[antlr-interest] Re: nondeterminism question

[Bill Canfield]

Hi Klaas:

I haven't looked at your grammar in detail, but be aware that ANTLR uses 
"linear approximate" lookahead.  In a nutshell, you might have an 
unambiguous grammar that looks ambiguous to ANTLR because it took a 
shortcut in calculating the rule.  Higher values of k tend to produce 
more of these false ambiguities.

Here's a note on it in the ANTLR docs:

http://www.antlr.org/doc/options.html#_bb4

When I've had a situation like this, I just factor the rule until I get 
ANTLR to behave :-).

Bill

Klaas Hofstra wrote:

> When you say 'grouped expression', do you mean 'LPAREN expression RPAREN' ?
> 
> Because bitSliceExpression can only follow a 'primaryExpression' or 'LPAREN 
> expression RPAREN!' I thought it could be distinguised from a grouped 
> expression. Am I missing something?
> 
> I changed k to 3. This resulted in the following warning at the same line as 
> before:
> 
> warning:nondeterminism between alts 1 and 2 of block upon
>   k==1:LPAREN
>   k==2:ID,LPAREN,INT,REAL,PLUS,MINUS,"not","cast"
>   k==3:ID,LT,GT,LPAREN,LBRACKET,INT,REAL,"signed","unsigned","float",
>             "integer","enum",DOTDOT,"and","or","nand","nor","xor","xnor",
>             EQUALS,NOT_EQUALS,GTE,LTE,"sll","srl","sla","sra","rol","ror",
>             PLUS,MINUS,TIMES,DIV,"mod","not","cast"
> 
> Looking at the above warning, I guess there is a problem with the expressions 
> in 'range' but I don't get why.
> 
> Anyone?
>