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Optional arguments [message #1009506]

Fri, 15 February 2013 08:47

Gaspar Din

Messages: 21
Registered: September 2012

Junior Member

Hi,

in my grammar there is a definition Func which can hold 0 to n params.
Simplified xtext fragment:

Func: {Func} '(' ( params+=INT(',' params+=INT)* )? ')' ';';

This allows to edit code like:

Func(4, 5, 10);

Now I want some parameters to be optional to edit code like:

Func (7, , 15);

My question:
How can I change the grammar to omit single params? It then must be possible accessing the values where the omitted values keep some empty/null value like:
params[0] // value is 7
params[1] // value is empty/null
params[2] // value is 15

Therefore, I can not make the single params completely optional like
(params+=INT)? // this would not set an empty/null value to an omitted param

Any suggestions?
Thanks in advance,
Gaspar

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Re: Optional arguments [message #1009585 is a reply to message #1009506]

Fri, 15 February 2013 10:50

Alexander Nittka

Messages: 1193
Registered: July 2009

Senior Member

Hi,

(params+=INT)? makes the assignment optional, not only the text

params+=INT? should work

Alex

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Re: Optional arguments [message #1009689 is a reply to message #1009585]

Fri, 15 February 2013 14:28

Gaspar Din

Messages: 21
Registered: September 2012

Junior Member

Hi Alexander,

first, thank you for the quick answer.

But unfortunately, when I define
Func: {Func} '(' ( params+=INT(',' params+=INT?)* )? ')' ';';
it is really possible editing
Func (7, , , 15);
but calling func.getParams() only holds the two values 7 and 15.
The size of func.getParams() is two.

But how can I find out at which position the arguments are located?

Regards,
Gaspar

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Re: Optional arguments [message #1009694 is a reply to message #1009689]

Fri, 15 February 2013 14:37

Christian Dietrich

Messages: 14667
Registered: July 2009

Senior Member

Hi,

what about

import "http://www.eclipse.org/emf/2002/Ecore" as ecore

Func: {Func} '(' ( params+=INT( params+=OINT)* )? ')' ';';
OINT returns ecore::EInt: ',' INT?;

and a custom valueconverter that handles the "null/strip away the comma" problem

Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

[Updated on: Fri, 15 February 2013 14:41]

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