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Keyword clashing with terminal rule [message #1858872]

Thu, 27 April 2023 08:58

Eclipse User

I have a data rule containing the keyword '/':

MultiplicativeOperation returns Expression:
	BinaryOperation ( =>({ArithmeticOperation.left=current} operator=('*'|'/')) right=RosettaCalcBinary)*
;

Now I wanted to add support for JavaScript like regular expressions, e.g., `/[a-b]+/`. I added the following terminal rule for it:

terminal PATTERN returns Pattern:
	'/' ( '\\' . | !('\\'|'/') )* '/'
;

(given `type Pattern wraps Pattern` in Xcore)

However, now the `MultiplicativeOperation` rule doesn't work anymore. Any occurences of a division "a / b" results in a syntax error "mismatched character '<EOF>' expecting '/'".

Is there a way around this?

Re: Keyword clashing with terminal rule [message #1858873 is a reply to message #1858872]

Thu, 27 April 2023 09:02

Eclipse User

i dont think this is solvable without introducing a stateful lexer (you migh look into jflex)

Re: Keyword clashing with terminal rule [message #1858874 is a reply to message #1858873]

Thu, 27 April 2023 09:03

Eclipse User

or you check if you can reuse https://github.com/eclipse/n4js/blob/master/plugins/org.eclipse.n4js/src/org/eclipse/n4js/parser/RegExLiteralAwareLexer.java

Re: Keyword clashing with terminal rule [message #1858875 is a reply to message #1858874]

Thu, 27 April 2023 09:17

Eclipse User

I feared this was gonna be hard. Thank you for the quick response and the references.

Re: Keyword clashing with terminal rule [message #1858883 is a reply to message #1858875]

Fri, 28 April 2023 03:37

Eclipse User

When grammar tooling starts to fail, it is often a forewarning that there are ambiguous syntaxes that will not always be parsed in accordance with your user's expectations.

It is obviously possible to make a regex look like all sorts of regular grammar.

Better to introduce something distinctive such as a 'regex' keyword prefix or surrounding quotes. Just imagine 'improving' the Java grammar to support call of the regex support without quotes.

Re: Keyword clashing with terminal rule [message #1858948 is a reply to message #1858872]

Tue, 02 May 2023 15:46

Eclipse User

This case works for me

grammar org.xtext.example.mydsl.MyDsl hidden(WS)

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

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

Model:Test;
Test: value+=(MultiplicativeOperation | Pattern)+;
BinaryOperation: value=INT;
RosettaCalcBinary: value=INT;

MultiplicativeOperation returns Expression: BinaryOperation ( =>({ArithmeticOperation.left=current} operator='*' | '/') right=RosettaCalcBinary)*;

Pattern:	{Pattern} '/' P_BODY '/';

terminal INT returns ecore::EInt: ('0'..'9')+;
terminal P_BODY: ( '\\' | '\\*' | '\\/' | !('\\'|'/'|'*'|' '|'\t'|'\r'|'\n') )+ ;
terminal WS: (' '|'\t'|'\r'|'\n')+;

Re: Keyword clashing with terminal rule [message #1858949 is a reply to message #1858948]

Tue, 02 May 2023 15:56

Eclipse User

to modify in previous message:

MultiplicativeOperation returns Expression: BinaryOperation ( =>({ArithmeticOperation.left=current} operator=('*'|'/')) right=RosettaCalcBinary)*

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