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Tue, 02 March 2021 12:49

Eclipse User

I'm trying to develop a DSL that uses JSON. But I've run into a problem with the following grammar:

grammar org.xtext.example.mydsl.MyDsl hidden(WS, ML_COMMENT, SL_COMMENT)

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

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

Model:
'[' objects += Object (',' objects += Object)* ']'
;

Object:
'{' '"name"' ':' '"' name = STRING '"' ',' '"type"' ':' '"object"' ',' '"isOptional"' ':' value = BOOLEAN ',' '"dataType"' ':' '"' dataType = PredefinedType '"' '}'
;

PredefinedType:
type = ('String' | 'int' | 'float' | 'boolean')
;

terminal STRING: "'" ( '\\' . /* 'b'|'t'|'n'|'f'|'r'|'u'|'"'|"'"|'\\' */ | !('\\'|"'") )* "'";

terminal BOOLEAN: 'true' | 'false';

terminal ML_COMMENT : '/*' -> '*/';

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

terminal WS : (' '|'\t'|'\r'|'\n')+;

terminal ANY_OTHER: .;

The DSL:
[
{
"name": "'Test'",
"type": "object",
"isOptional": false,
"dataType" : "int"
}
]

It gives error "mismatched charachter 'n' expections 's'" at int. It want me to write isOptional instead of int. I've tried changed '"isOptional"' to '"optional"' in the grammar, which fixes the issue. But I'm curious about why I get the error, and why changing the keyword fixes it. Any ideas?

[Updated on: Tue, 02 March 2021 12:51] by Moderator

Re: Mismatched character [message #1838640 is a reply to message #1838634]

Tue, 02 March 2021 13:37

Eclipse User

the lexer is greedy and thus cannot handle

'"isOptional"' vs '"' 'int' '"'

you can either enable backtracking

parserGenerator = {
options = {
backtrackLexer = true
}
}

or use terminals consistently

e.g.
Object:
'{' '"name"' ':' '"' name = STRING '"' ','
'"type"' ':' '"object"' ','
'"isOptional"' ':' value = BOOLEAN ','
'"dataType"' ':' dataType = PREDEFINED_TYPE '}'
;

terminal PREDEFINED_TYPE:
'"' ('String' | 'int' | 'float' | 'boolean')'"'
;

Re: Mismatched character [message #1838645 is a reply to message #1838640]

Tue, 02 March 2021 15:18

Eclipse User

Thanks, the last solution worked.

Why exactly can it not not differ '"isOptional"' vs '"' 'int' '"'?

Re: Mismatched character [message #1838649 is a reply to message #1838645]

Tue, 02 March 2021 23:26

Eclipse User

The first is a lever rule the second a parser rule

The file is Lexed completely first
Thus when the Lexer see
"i it goes the "isOptional path as it is greedy and won't create two tokens one for " and one for int

Re: Mismatched character [message #1838670 is a reply to message #1838649]

Wed, 03 March 2021 06:03

Eclipse User

Thanks for the explanation!

I've encountered another problem. I try to make it so the user can define their own types. dataType can then either be a predefined type or an already defined type.

If I do the following, I get a "NullPointerException: null" at the beginning of the grammar. You know why?

Model:
'[' objects += Object (',' objects += Object)* ',' '{' '"definedType"' ':' definedType = DefinedType '}' ']'
;

Object:
'{' '"name"' ':' '"' name = STRING '"' ',' '"type"' ':' '"object"' ',' '"isOptional"' ':' value = BOOLEAN ',' '"dataType"' ':' dataType = ([DefinedType|STRING] | PREDEFINED_TYPE) '}'
;

DefinedType:
'"' name = STRING '"'
;

terminal PREDEFINED_TYPE:
'"' ('String' | 'int' | 'float' | 'boolean') '"';

terminal STRING: "'" ( '\\' . /* 'b'|'t'|'n'|'f'|'r'|'u'|'"'|"'"|'\\' */ | !('\\'|"'") )* "'";

[Updated on: Wed, 03 March 2021 12:11] by Moderator

Re: Mismatched character [message #1838800 is a reply to message #1838670]

Fri, 05 March 2021 03:47

Eclipse User

Re: Mismatched character [message #1838801 is a reply to message #1838800]

Fri, 05 March 2021 03:59

Eclipse User

dataType = ([DefinedType|STRING] | PREDEFINED_TYPE is an antipattern.
without a stacktrace hard to jude

maybe

dataType =AbstractDataType

AbstractDataType: PrimiteDataType | DataTypeRef;

PrimiteDataType: type= PREDEFINED_TYPE;
DataTypeRef: ref=[DefinedType|STRING];

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