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How to restrict a rule [message #1058265]

Mon, 13 May 2013 12:16

rohit ahuja

Messages: 27
Registered: February 2013

Junior Member

I have something like,

Model
exp1= EXPRESSION '+' exp2=EXPRESSION

where EXPRESSION handles all kind of possible cases that i require.

Now the problem is that '+' is also part of an expression, and exp1 basically spans across the '+' symbol and consumes the exp2 as well.

is it possible to do this in some other way?

Thanks,
Rohit

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Re: How to restrict a rule [message #1058447 is a reply to message #1058265]

Tue, 14 May 2013 07:19

Colonel Panic

Messages: 7
Registered: May 2013

Junior Member

Before you can answer this question you need to decide for yourself how the compiler should decide which expression belongs in which side of the AST. For example, should it parse:

a + b + c

exp1='a' '+' exp2='b + c'

exp1='a + b' '+' exp2='c'

Until you can decide this for yourself, there isn't a general case answer to your problem.

It may be the case that you are trying to put too much validation into the parser. Consider parsing 'EXPRESSION + EXPRESSION' in a single rule, rather than two, then deciding in your model validation and/or inference which version of the rule is intended (according to rules of your own choosing).

Hope that helps!

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Re: How to restrict a rule [message #1058461 is a reply to message #1058447]

Tue, 14 May 2013 08:43

Christian Dietrich

Messages: 6639
Registered: July 2009

Senior Member

This might help as well
http://blog.efftinge.de/2010/08/parsing-expressions-with-xtext.html

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