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Whitespace-Aware Languages with unindented Single line comment [message #1748565]

Thu, 24 November 2016 08:04

Eclipse User

Hello Folks,

I am currently working on a Whitespace-Aware Language (YAML-Style).

Now i would like to allow comments to have any indentation without it triggering the BLOCK_END synthetic. How would i do this properly?

e.g. in the homeautomation example i want my Grammar to accept following:

Device Window can be open, closed
 
Device Heater can be on, off, error
 
Rule 'Save energy' when Window.open then
//fire(Heater.off)
  fire(Heater.off)

Which with the untouched example project results in having the second fire(Heater.off) highlighted with the error missing RULE_BEGIN at 'fire'

Thanks for the input.

regards,
Stefan

Re: Whitespace-Aware Languages with unindented Single line comment [message #1748692 is a reply to message #1748565]

Sun, 27 November 2016 03:22

Eclipse User

you could try do adapt SL_COMMENT rule to eat up the newline before and not to eat up the newline after
this should at least work in the most cases

terminal SL_COMMENT:
('\n'|'\r')?'//' !('\n'|'\r')*
;

Re: Whitespace-Aware Languages with unindented Single line comment [message #1748857 is a reply to message #1748692]

Tue, 29 November 2016 07:09

Eclipse User

Hi Christian,

Thanks for your response. Sadly this does not resolve the issue i have.

Referring to following home-automation example this still gives me the error "missing RULE_BEGIN at 'fire'":

Device Window can be open, closed
 
Device Heater can be on, off, error
 
Rule 'Save energy' when Window.open then
  fire(Heater.off)
// Some comment
  fire(Heater.off)

Do you have any other ideas on how to tackle this?

Regards,
Stefan

Edit: edited the example-syntax

[Updated on: Tue, 29 November 2016 07:19] by Moderator

Re: Whitespace-Aware Languages with unindented Single line comment [message #1748859 is a reply to message #1748857]

Tue, 29 November 2016 07:34

Eclipse User

no i dont

Re: Whitespace-Aware Languages with unindented Single line comment [message #1748918 is a reply to message #1748859]

Wed, 30 November 2016 02:35

Eclipse User

I don't see your grammar, but ...
is it correct that fire(Heater.off) appears twice?

Re: Whitespace-Aware Languages with unindented Single line comment [message #1748928 is a reply to message #1748918]

Wed, 30 November 2016 04:02

Eclipse User

Hi Uli,

Its the grammar of the Home-Automation example included in xText. The only thing i changed is the SL_COMMENT terminal as recommended by Christian.

For the sake of completeness:

/*******************************************************************************
 * Copyright (c) 2015 itemis AG (http://www.itemis.eu) and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *******************************************************************************/
grammar org.eclipse.xtext.example.homeautomation.RuleEngine with org.eclipse.xtext.xbase.Xbase

import "http://www.eclipse.org/xtext/xbase/Xbase" as xbase
generate ruleEngine "http://www.eclipse.org/Xtext/example/RuleEngine"

Model:
	declarations+=Declaration*;
	
terminal SL_COMMENT:
  ('\n'|'\r' )  '//' !('\n'|'\r')*
;

Declaration:
	Device | Rule;

Device:
	'Device' name=ID 'can' 'be'
		(states+=State (',' states+=State)*)?;

State:
	name=ID ;

Rule:
	'Rule' description=STRING
		'when' deviceState=[State|QualifiedName]
		'then' thenPart=XBlockExpression;

// We modify the concrete syntax of two Xbase expressions and make them indentation-aware
XBlockExpression returns xbase::XExpression: 
	{xbase::XBlockExpression}
	BEGIN
		(expressions+=XExpressionOrVarDeclaration ';'?)*
	END;

XSwitchExpression returns xbase::XExpression:
	{xbase::XSwitchExpression}
	'switch' (=>('(' declaredParam=JvmFormalParameter ':') switch=XExpression ')'
		| =>(declaredParam=JvmFormalParameter ':')? switch=XExpression)
	BEGIN
		(cases+=XCasePart)*
		('default' ':' default=XExpression )?
	END;

// The following synthetic tokens are used for the indentation-aware blocks
terminal BEGIN: 'synthetic:BEGIN';  // increase indentation
terminal END: 'synthetic:END';      // decrease indentation

Re: Whitespace-Aware Languages with unindented Single line comment [message #1748930 is a reply to message #1748928]

Wed, 30 November 2016 04:07

Eclipse User

So what i think would help is if i modify the SL_COMMENT terminal to consume not only the newline but all whitespaces before the comment. Something like this:

terminal SL_COMMENT:
WS? '//' !('\n'|'\r')*
;

But now when i open a .rule file in eclipse i get the error:
Failed to create the part's controls

java.lang.NullPointerException
at org.eclipse.xtext.ui.editor.toggleComments.SLCommentPrefixCalculator.caseGroup(SLCommentPrefixCalculator.java:43)
at org.eclipse.xtext.ui.editor.toggleComments.SLCommentPrefixCalculator.caseGroup(SLCommentPrefixCalculator.java:1)
at org.eclipse.xtext.util.XtextSwitch.doSwitch(XtextSwitch.java:225)
at org.eclipse.emf.ecore.util.Switch.doSwitch(Switch.java:53)
at org.eclipse.emf.ecore.util.Switch.doSwitch(Switch.java:69)
at org.eclipse.xtext.ui.editor.toggleComments.DefaultSingleLineCommentHelper.calculatePrefixes(DefaultSingleLineCommentHelper.java:54)
at org.eclipse.xtext.ui.editor.toggleComments.DefaultSingleLineCommentHelper.getDefaultPrefixes(DefaultSingleLineCommentHelper.java:48)
at org.eclipse.xtext.ui.editor.XtextSourceViewerConfiguration.getDefaultPrefixes(XtextSourceViewerConfiguration.java:249)
at org.eclipse.jface.text.source.SourceViewer.configure(SourceViewer.java:526)
at org.eclipse.ui.texteditor.AbstractTextEditor.createPartControl(AbstractTextEditor.java:3360)
.
.
.

Re: Whitespace-Aware Languages with unindented Single line comment [message #1748949 is a reply to message #1748930]

Wed, 30 November 2016 06:09

Eclipse User

... your rule only allows a single "then fire(heater.off)"

But the DSL file causing the error reads (excluding the comment) "then fire(heater.off) fire(heater.off)"

Re: Whitespace-Aware Languages with unindented Single line comment [message #1748959 is a reply to message #1748949]

Wed, 30 November 2016 08:52

Eclipse User

Hi Uli,

Thanks for your response. The repetition of Expressions or Variable declarations are not the problem here.

The then part of the rule 'Rule' consists of a XBlockExpression:

Rule:
	'Rule' description=STRING
		'when' deviceState=[State|QualifiedName]
		'then' thenPart=XBlockExpression;

Which is a block filled with zero or many XExpressionOrVariableDeclaration:

XBlockExpression returns xbase::XExpression: 
	{xbase::XBlockExpression}
	BEGIN
		(expressions+=XExpressionOrVarDeclaration ';'?)*
	END;

This makes this .rules file valid under the grammar:

Device Window can be open, closed
 
Device Heater can be on, off, error

Rule 'Save energy' when Window.open then
  var someDeclaration = "Anystring";
  fire(Heater.off)
  // Some Comment
  main(["mainArgs..."]);

But this is not because of the aforementioned problem considering block statements and comments:

Device Window can be open, closed
 
Device Heater can be on, off, error

Rule 'Save energy' when Window.open then
  var someDeclaration = "Anystring";
  fire(Heater.off)
// Some Comment
  main(["mainArgs..."]);

What i would like is to have comments similar to most WS aware languages such as e.g. phyton whereas this is a syntactically valid program:

x = 1
if x == 1:
    print("x is 1.")
# syntactically correct comment line
    print("some other output")

Regards,
Stefan

edit: i fixed some typos.

[Updated on: Wed, 30 November 2016 08:53] by Moderator

Re: Whitespace-Aware Languages with unindented Single line comment [message #1748973 is a reply to message #1748959]

Wed, 30 November 2016 11:11

Eclipse User

OK, I understand.

So the problem is that the comment is not as much indented
as the previous statement and therefore the parser raises the "END" of the Block

Re: Whitespace-Aware Languages with unindented Single line comment [message #1749026 is a reply to message #1748973]

Thu, 01 December 2016 04:32

Eclipse User

Yes. That is the problem.

Now, a clean approach towards a solution would be of interest. Do you have any input?

Re: Whitespace-Aware Languages with unindented Single line comment [message #1749043 is a reply to message #1749026]

Thu, 01 December 2016 07:27

Eclipse User

perhaps the following extension to your grammar may help?
a NL to get it started, perhaps spaces and tabs, then the // followed by the rest of the line?

terminal SL_COMMENT:
('\n'|'\r' )(' '|'\t')* '//' !('\n'|'\r')*

instead of your
terminal SL_COMMENT:
WS? '//' !('\n'|'\r')*

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