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[TCS] How to define empty string ? [message #10145]

Tue, 15 April 2008 12:12

Eclipse User

Originally posted by: romain.perruchon.thalesgroup.com

Hi,

I have lines defines like this :

template Ligne
: aa";"bb";"cc";"dd";"ee
;

My language can contain lines like this :
;;xxx;yyy;zzz

with empty values between ";"

How can I explain in my tcs these possibly empty values ?
I try several manner in the lexer to define STRING but fail.

I have this actually :

STRING
:
(
~(';' |'\\\\'|'\\''|'\\n')
)*
;

This works with lines without empty values.

Thanks

Re: [TCS] How to define empty string ? [message #10166 is a reply to message #10145]

Wed, 16 April 2008 03:24

Eclipse User

Hi,

Generally, if you have a specific construct in the concrete syntax, it
corresponds to a specific construct in the metamodel.

For instance, given program:
aa;bb;;cc;dd;;;ee;

you could create the following metamodel:

class List {
reference elements[*] ordered container : Element;
}

abstract class Element {}

class NamedElement extends Element {
attribute name : String;
}

class EmptyElement extends Element {}

and the following TCS model:

template List main
: elements
;

template Element abstract;

template NamedElement
: name ";"
;

template EmptyElement
: ";"
;

This pattern can for instance be used to represent statements and empty
statements in languages that support this.

When transforming a program with empty elements, you can decide whether
you want to ignore empty elements or not. However, if you made this
decision at the TCS level you would already do some structural change.

Regards,

Frédéric Jouault

romain Perruchon a écrit :
> Hi,
>
> I have lines defines like this :
>
> template Ligne
> : aa";"bb";"cc";"dd";"ee
> ;
>
> My language can contain lines like this :
> ;;xxx;yyy;zzz
>
> with empty values between ";"
>
> How can I explain in my tcs these possibly empty values ?
> I try several manner in the lexer to define STRING but fail.
>
> I have this actually :
>
> STRING
> :
> (
> ~(';' |'\\\\'|'\\''|'\\n')
> )*
> ;
>
> This works with lines without empty values.
>
> Thanks
>

Re: [TCS] How to define empty string ? [message #12250 is a reply to message #10166]

Wed, 16 April 2008 05:29

Eclipse User

Originally posted by: romain.perruchon.thalesgroup.com

Thanks for reply frederic.

It was simple but I didn't think like this. I understand now my mistake.

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