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let
class Exp
{
var id : int := 0
method id_get() : int = self.id
method accept(v : Visitor) = ()
}
class AssignExp extends Exp
{
var expression : string := "var foo := bar"
method get_expression() : string = self.expression
method set_expression(new_expr : string) = (self.expression = new_expr; ())
}
class Visitor
{
method visit(e : Exp) = print_int(e.id_get())
}
class PrintVisitor extends Visitor
{
method visit(e : AssignExp) = print(e.get_expression())
}
var exp := new AssignExp
var visitor := new PrintVisitor
in
exp.accept(visitor);
exp.set_expression("var bar := foo");
exp.accept(visitor)
end
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