[antlr-interest] Can't express a obvious thing in ANTLR tree rewriting syntax

[John B. Brodie]

Greetings!

On 12/05/2011 01:17 PM, Stefan Mätje wrote:
> Hi,
>
> I unfortunately can't express what I want in ANTLR syntax. It should be  
> obvious but I
> can't see the solution at the moment. I want to build an AST while parsing  
> generating
> a VAR_DCL imaginary node for a variable declaration and an ARRAY_DCL imaginary  
> node
> for an array declaration.
>
> Here are some example declarations and the expected AST:
> DCL var		FIXED;	-> (VAR_DCL FIXED MOD_LIST var)
> DCL array  (10)	FIXED;	-> (ARRAY_DCL ^(DIM_LIST BOUND 1 10) FIXED MOD_LIST  
> array)
>
> The language itself is not ambigious at this point of the grammar so it should  
> be possible
> to simply write the solution down without using syntactic or semantic  
> predicates. But I
> don't see how to solve it in the rule "dclSet". Possible semantic predicate  
> marked with
> "???CONDITION???".
>
> I have the following parts of a lexer/parser grammar:
>
> /**	"VariableDeclaration"
> 	*/
> var_dcl:
> 	KW_DCL!			// "DCL"
> 	dclSet (',' dclSet)*
> 	';'!
> 	;
>
> /**	"DeclareSentence"
> */
> dclSet:
> 	ids=oneIdOrList dimAttr? i='INV'? simpleType globalAttr? initAttr?
> 		-> {???CONDITION???}?	^(ARRAY_DCL $dimAttr simpleType  
> ^(MOD_LIST $i? globalAttr?) $ids+)
> 		-> 			^(VAR_DCL simpleType ^(MOD_LIST $i?  
> globalAttr?) $ids+)
> 	;
>
> /** "OneIdentifierOrList"
> */
> oneIdOrList:
> 	( ID | '(' ID (',' ID )* ')' )	-> ID+
> 	;
>
> /**	"DimensionAttribute"
> 	The dimension boundaries for an array.
> 	*/
> dimAttr:
> 	LPAREN dimBound ( ',' dimBound )* RPAREN	-> ^(DIM_LIST  
> dimBound+)
> 	;
>
> /**	"DimensionBoundaries"
> 	BOUND carries always two expressions for the LWB and UPB. If the LWB
> 	is not specified it is substituted as FIX_LIT with value 1. This is
> 	an "integer".
> */
> dimBound
> 	:	lwb=constFixExpr COLON upb=constFixExpr	-> BOUND[$lwb.start]  
> $lwb $upb
> 	|	upb=constFixExpr	-> BOUND[$upb.start]  
> FIX_LIT[$upb.start,"1"] PRSZ["15"] $upb
> 	;
>
just a simple flag...

dclSet @init{boolean array=false;} :
    ids=oneIdOrList (dimAttr{array=true;})? i='INV'? simpleType
globalAttr? initAttr?
        -> {array}? ^(ARRAY_DCL dimAttr simpleType ^(MOD_LIST $i?
globalAttr?) $ids+)
        ->          ^(VAR_DCL simpleType ^(MOD_LIST $i? globalAttr?) $ids+)
    ;

(BTW, did you mean to leave initAttr out of the tree?)

hope this helps
   -jbb