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When to use XExpression, XblockExpression and just plain parser rule [message #1736257]

Mon, 27 June 2016 22:57

Mansour Al

Messages: 44
Registered: June 2016

Member

I have been prototyping and playing with xText/Xbase for few weeks. I am still lost as there are many components in the system that I have not seen.

Now, I would to understand when to use an XExpression, and when not use it. And if I need an expression, why not use XBlockExpression.

So what factors others use to decide if they need to use an expression or not.

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Re: When to use XExpression, XblockExpression and just plain parser rule [message #1736267 is a reply to message #1736257]

Tue, 28 June 2016 07:01

Karsten Thoms

Messages: 762
Registered: July 2009
Location: Dortmund, Germany

Senior Member

Usually DSLs won't make any restriction on the kind of expression they allow at a certain position, so XExpression is often right. But if you would like to force that an expression has to be encapsulated in curly brackets, you go with XBlockExpression. For example, if you would like something like an Operation which has a Body, as seen in the Domainmodel example.

As always, it depends...

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Re: When to use XExpression, XblockExpression and just plain parser rule [message #1736293 is a reply to message #1736267]

Tue, 28 June 2016 09:53

Mansour Al

Messages: 44
Registered: June 2016

Member

Karsten,
Thank you a lot.
I understand that XExpression can be created any where. But when do I use

MyElement returns XExpression:
{MyElement} ......

And when to use

MyElement:
{MyElement} .......

Thank you

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Re: When to use XExpression, XblockExpression and just plain parser rule [message #1736302 is a reply to message #1736293]

Tue, 28 June 2016 10:29

Christian Dietrich

Messages: 14665
Registered: July 2009

Senior Member

MyElement returns XExpression makes your expression an xexpression so that

- it can be used as initializer of a field or a body of a method, can be handled by typecomputer etc.

MyElement:
{MyElement}

does not

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

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