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The Assignment Problem: Elegantly

... imperative type-based dispatch ... facility of the C++ language

expression : expression ASSIGN expression { $$ = context->expression_assignment($1, $3); } ;

expression : expression ASSIGN expression { $$ = $1->expression_assignment($3); } ;

void translator::expression_assignment(expression *lhs, expression *rhs) {

class expression { public: virtual expression *assignment_expression(expression *rhs); };

expression_ldl *t1 = dynamic_cast<expression_ldo>(lhs) if (t1) return new expression_sro(t1->get_address(), rhs);

expression * expression_ldo::assignment_factory(expression *rhs) { return new expression_sro(address, rhs); }

etc etc etc etc etc etc

yyerror("left hand side of assignment inappropriate"); return new expression_error(); }

expression * expression::assignment_factory(expression *) { yyerror("left hand side of assignment inappropriate"); return new expression_error(); }

Now you have a translator class that can manufacture an expression class that can manufacture another expression class.
You have a factory factory.

... imperative type-based dispatch	... facility of the C++ language
expression : expression ASSIGN expression { $$ = context->expression_assignment($1, $3); } ;	expression : expression ASSIGN expression { $$ = $1->expression_assignment($3); } ;
void translator::expression_assignment(expression lhs, expression rhs) {	class expression { public: virtual expression assignment_expression(expression rhs); };
expression_ldl *t1 = dynamic_cast<expression_ldo>(lhs) if (t1) return new expression_sro(t1->get_address(), rhs);	expression * expression_ldo::assignment_factory(expression *rhs) { return new expression_sro(address, rhs); }
etc etc etc	etc etc etc
yyerror("left hand side of assignment inappropriate"); return new expression_error(); }	expression * expression::assignment_factory(expression *) { yyerror("left hand side of assignment inappropriate"); return new expression_error(); }
Now you have a translator class that can manufacture an expression class that can manufacture another expression class. You have a factory factory.