[antlr-interest] unary minus

[Johannes Luber]

> Hi,
> 
> I've just turned to ANTLR and everything looks very nice. Except, I
> have some problems with my implementation of unary minus. Can anyone
> help me with the following errors?

I think the problem is with the rules

arithmeticExpr
    :    sumExpr ( addSubOp^ sumExpr )*
    ;

factorExpr
    :    (MINUS^)? atom
    ;

With the input "5 - 3" ANTLR doesn't know if it should match factorExpr with a MINUS or use addSubOp instead. Looking at my C# grammar, it uses the following (simplified) rule

unary_expression
	:	primary_expression
	|	PLUS unary_expression
	|	MINUS unary_expression
	;

Looking at primary_expression  I'd say it is the equivalent of the atom rule. So try the following change:

factorExpr
    :    atom
    :    MINUS^ factorExpr
    ;

Johannes
> 
> [16:11:03] error(211): McAntlrExpression.g:61:32: [fatal] rule
> arithmeticExpr has non-LL(*) decision due to recursive rule
> invocations reachable from alts 1,2.  Resolve by left-factoring or
> using syntactic predicates or using backtrack=true option.
> [16:11:03] warning(200): McAntlrExpression.g:61:32: Decision can match
> input such as "MINUS INTEGER" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
> 
> Here is my grammar:
> 
> grammar McAntlrExpression;
> options {
> 	output=AST;
> 	ASTLabelType=CommonTree;
> //    backtrack=true;
> //    memoize=true;
> }
> prog:	( orExpr	{ System.out.println($orExpr.tree.toStringTree()); } )+
> 	;
> 
> orExpr
> 	:	andExpr ( OR^ andExpr )*
> 	; 	
> 
> andExpr
> 	:	equalityExpr ( AND^ equalityExpr )*
> 	;
> 
> equalityExpr
> 	:	notExpr ( equalityOp notExpr )*
> 	;	
> 	
> notExpr
> 	:	NOT^ boolExpr
> 	|	boolExpr
> 	;
> 
> boolExpr
> 	:	BOOLEAN
> 	|	relationalExpr
> 	;
> 
> relationalExpr
> 	:	arithmeticExpr ( relationalOp^ | equalityOp^ arithmeticExpr )
> 	;
> 
> arithmeticExpr
> 	:	sumExpr ( addSubOp^ sumExpr )*
> 	;
> 	
> sumExpr
> 	:	factorExpr ( mulDivOp^ factorExpr )*
> 	;
> 	
> factorExpr
> 	:	(MINUS^)? atom
> 	;
> 
> relationalOp
>     :	LT
>     |	GT
>     |	LE
>     |	GE
>     ;
> 
> equalityOp
> 	:	EQ
> 	|	NEQ
> 	;
> 
> addSubOp
> 	:	PLUS
> 	|	MINUS
> 	;
> 
> mulDivOp
> 	:	MULT
> 	|	DIV	;
> 
> atom
>     :   INTEGER
>    	|   LP! arithmeticExpr RP!
>     ;
> 
> LT 	:	'<';
> GT 	:	'>';
> LE	:	'<=';
> GE	:	'>=';
> EQ	:	'=';
> NEQ	:	'!=';
> PLUS:	'+';
> MINUS
> 	:	'-';
> MULT:	'*';
> DIV	:	'/';
> LP	:	'(';
> RP	:	')';
> NOT	:	'not';
> AND	:	'and';
> OR	:	'or';
> INTEGER
> 	:	'0'..'9'+ ;
> BOOLEAN	:	'true' | 'false';
> CONSTANT  :   ('a'..'z'|'A'..'Z')+ ;
> NEWLINE:'\r'? '\n' ;
> WS  :   (' '|'\t')+ {skip();} ;
> 
> -- AH
> 
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