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Resolving conflicts with terminals and rules [message #557191]

Sun, 05 September 2010 23:23

Nikolay

Messages: 2
Registered: September 2010

Junior Member

I have the task to support Integer, Identifier and Color in my language. Color is the hex number without any prefix and quotes, i.e "221122" or "FFAA33".

I'm new with xText but hoped that this task has the simple solution. Unfortunatly my attempts to solve it gave me nothing but boring conflicts between INT, Color and ID rules. I can even understand why I have problems, but I don't understand how to overcome them.

Here is my grammar file with my attempts commented and marked with number from 1 to 3. I have simplified color to ColorComponent which has 2 digits instead of 6.

grammar org.xtext.example.mydsl.MyDsl with org.eclipse.xtext.common.Terminals 

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

generate myDsl "http://www.xtext.org/example/mydsl/MyDsl"

Model :
	(options += Option)*;
	
IntTest :
	'-int' myint = INT;
	
MyColor :
	'-green' green = ColorComponent;	
	
MyIdent:
	'-ident' ident = ID;	
    
Option:
	MyColor | IntTest | MyIdent;

// 1. 
// "-ident FF" has error "mismatched input 'FF' expecting RULE_ID"
// "-int 1" has error "mismatched input '1' expecting RULE_INT"
// terminal HexDigit : ('0' .. '9') | ('A' .. 'F');
// terminal ColorComponent : HexDigit HexDigit;

// 2. 
// "-green FF" has error "mismatched input 'FF' expecting RULE_HEXDIGIT"
// "-int 1" has error "mismatched input '1' expecting RULE_INT"
//ColorComponent :
//	HexDigit HexDigit;
//	
//terminal HexDigit : ('0' .. '9') | ('A' .. 'F');

// 3.
// "-green FF" has error "mismatched input 'FF' expecting RULE_HEXDIGIT"
// "-int 1" has error "mismatched input '1' expecting RULE_INT"
//ColorComponent:
//  (HexDigit HexDigit);	
//	
//terminal Digit : ('0'..'9');	
//terminal HexDigit : (Digit) | ('A' .. 'F');
//terminal INT returns ecore::EInt: (Digit)+;

Each decision was tested with file

-int 1
-green FF
-ident FF

Please could someone give me a hint how to deal with such problem?

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Re: Resolving conflicts with terminals and rules [message #557244 is a reply to message #557191]

Mon, 06 September 2010 09:04

Alexander Nittka

Messages: 1193
Registered: July 2009

Senior Member

Hi,

the main problem is that your terminal rules overlap. HexDigit hides
Digit and INTs of length 1.
What I would do (in this simple example) is not introduce any new
terminal rules and rather use data type rules along with semantic
validation in order to check the syntax.

ColorComponent hidden(): ID|INT ID;
(ID matches components starting with a lettern, INT ID those starting
with a number).

In the validation you then check whether "green" of "MyColor" has the
desired form. Alternatively you could also have a value converter for
ColorComponent throwing a corresponding exception if the String does not
have the correct form.

Alex

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