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Cannot use literal in following ID terminal rule [message #1067340]

Mon, 08 July 2013 11:10

kon f

Messages: 152
Registered: March 2012

Senior Member

Hey,

I encountered some parsing behavior that I do not understand. I cannot use some fixed literals in the following ID terminal rule. It can be visualized by the Hello World example:

Greeting:
	'Hello' name=ID '!';

also if I use Hello for the ID rule:

Hello Hello !

I get the error message: mismatched input 'Hello' expecting RULE_ID (the second Hello is marked)

Hello is a valid content for ID but it is still marked. How do I adjust the grammar the right way?

Thank you!

Kon

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Re: Cannot use literal in following ID terminal rule [message #1067344 is a reply to message #1067340]

Mon, 08 July 2013 11:22

Alexander Nittka

Messages: 1193
Registered: July 2009

Senior Member

Hi,

Hello is not a "valid" content for ID, as it is a keyword. Terminals may overlap and only one definition wins. If you want Hello to be a valid id you have to introduce a datatype rule

MyId: ID|'Hello';

and use that instead of ID for id features.

Alex

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Re: Cannot use literal in following ID terminal rule [message #1067348 is a reply to message #1067344]

Mon, 08 July 2013 11:41

kon f

Messages: 152
Registered: March 2012

Senior Member

Thank you Alex, that worked! Just the highlighting in the editor seems a bit strange Wink

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Re: Cannot use literal in following ID terminal rule [message #1067356 is a reply to message #1067348]

Mon, 08 July 2013 11:55

Claudio Heeg

Messages: 75
Registered: April 2013

Member

kon f wrote on Mon, 08 July 2013 13:41

Thank you Alex, that worked! Just the highlighting in the editor seems a bit strange

Keeping that issue in check gets especially difficult on case-insensitive grammars with lots of keywords.
Don't see how things could work otherwise, though, unless Lexing would be altered massively.
Or case-insentivity could be specified for only certain keywords (length>2 or so) - it might only be slightly related to the topic, but could such a thing be possible?

[Updated on: Mon, 08 July 2013 12:04]

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Re: Cannot use literal in following ID terminal rule [message #1067358 is a reply to message #1067348]

Mon, 08 July 2013 12:04

Alexander Nittka

Messages: 1193
Registered: July 2009

Senior Member

well, a keyword is a keyword (try naming a class class in Java). You can escape IDs

Hello ^Hello!

But of course this works only, if you have control over the language, i.e. you are not forced to make it work without escaping.

Alex

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Re: Cannot use literal in following ID terminal rule [message #1067360 is a reply to message #1067358]

Mon, 08 July 2013 12:07

Claudio Heeg

Messages: 75
Registered: April 2013

Member

I realise - sadly I don't have that control. Easy example could be SQL - we define a PRIMARY KEY and a table has an attribute called .key.
And selective case-insensitivity (see my edit above) couldn't be implemented easily, I'd reckon?

One would likely have to put that insensitivity into the grammar manually, by having ('SELECT'|'select')-keywords, I suppose..

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