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Grammar support [message #1823784]

Thu, 02 April 2020 06:03

Virag Purnam

Messages: 130
Registered: June 2014

Senior Member

Hi,

VarDecl:
	{VarDecl} 'int' newVar=NewVar ';'
;

NewVar:
	{NewVar} ('.' | '.EX')? IDENT
;

terminal IDENT:
			(('a'..'z'|'A'..'Z'|'_') ('^'|'a'..'z'|'A'..'Z'|'-'|'0'..'9')*)
 ;

With the above grammar, I am not able to declare variable.

int .Each;

, This throws error, as it expects 'X' after 'E'.
How to address this issue?

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Re: Grammar support [message #1823790 is a reply to message #1823784]

Thu, 02 April 2020 07:19

Ed Willink

Messages: 6874
Registered: July 2009

Senior Member

NewVar:
	{NewVar} ('.' 'EX'?)? IDENT
;

might fix it with an LL parser such as Xtext, but you'll be in bigger trouble with an LALR parser.

I strongly recommend that you review your grammar since you seem to have something confusing to tools which usually means something confusing to users. The tools provide a really good warning that your grammar is crazy.

What is

int .EXIT;

supposed to be? EX+IT or EXIT?

Regards

Ed Willink

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Re: Grammar support [message #1823793 is a reply to message #1823790]

Thu, 02 April 2020 07:34

Virag Purnam

Messages: 130
Registered: June 2014

Senior Member

Hi Mr. Ed Willink,

Thanks for the suggestion.
If the variable name starts with '.', then '.EXIT' will be treated as .EX - IT.
Is the grammar change proposed by you will satisfy the mentioned usecase.

Regards,
Virag

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Re: Grammar support [message #1823798 is a reply to message #1823793]

Thu, 02 April 2020 08:38

Ed Merks

Messages: 31539
Registered: July 2009

Senior Member

I think the point is that to "us" it seems like a confusing use case at best. Even if a variable name that happens to start with .EX has some semantic significance, I'd not try to build that significance into the grammar. If you want something in the grammar, better to use "." to mean whatever that is supposed to mean and to use "$' (or some other character not allowed at the start of an IDENT) to mean whatever you're planning to make ".EX" mean. It's just plan weird and confusing what you're trying to do where ".EX" looks just like a variable.

Ed Merks
Professional Support: https://www.macromodeling.com/

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