// The basic rule
decl
	: typename Identifier ('=' expression)? (',' Identifier ('=' expression)?)* ';'
	;

// The desired rewrite
decl
	: typename i+=Identifier ('=' e+=expression)? (',' i+=Identifier ('=' e+=expression)?)* ';'
		-> ^(DECL typename ^(ID $i)+ ^(EXPR $e)+
	;