Re: [Grammatica-users] token priority?

[Iain McGinniss]

Hi John,

In order to implement unary expressions I used a grammar structured like 
the following:

AdditiveExpression = MultiplicativeExpression AdditiveExpressionTail* ;
AdditiveExpressionTail = (ADD | SUB) MultiplicativeExpression ;

MultiplicativeExpression = UnaryExpression MultiplicativeExpressionTail* ;
MultiplicativeExpressionTail = (MUL | DIV) UnaryExpression ;

UnaryExpression = SUB ConstantOrPostfixExpression
   | ConstantOrPostfixExpression ;

Which, for a simple expression like -4 + 5 gives a parse tree of

AdditiveExpression
|->MultiplicativeExpression
  |->UnaryExpression
     |->SUB
     |->ConstantOrPostfixExpression (4)
|->AdditiveExpressionTail
  |->ADD
  |->MultiplicativeExpression
     |->UnaryExpression
        |->ConstantOrPostfixExpression (5)

It's been a while since I've touched this stuff but that's the gist of it.

Cheers,
Iain

John Ledbetter wrote:
> Hello,
>
> I am working with a grammar for a simple mathematical language, and I 
> am having trouble implementing a unary minus sign.
>
> In flex/bison, I would do something like...
>
> %left PLUS MINUS
> %nonassoc UNARY
>
> // ....
> somerule : expr MINUS expr
>              | MINUS expr %prec UNARY
>
>
> What is the equivalent construct in grammatica?
>
> Thanks,
> John.

________________________________________________________________________
This email (and any attachments) is private and confidential, and is intended 
solely for the
addressee. If you have received this communication in error please remove it 
and inform us via
telephone or email. Although we take all possible steps to ensure mail and 
attachments
are free from malicious content, malware and viruses, we cannot accept any 
responsibility
whatsoever for any changes to content outwith our administrative bounds. The 
views represented
within this mail are solely the view of the author and do not reflect the views 
of the organisation
as a whole.
________________________________________________________________________
Graham Technology plc                                                
http://www.grahamtechnology.com
________________________________________________________________________

Iain.McGinniss.vcf
Description: Vcard