use Red::AST; use Red::Column; class Red::AST::Constraint does Red::AST { has Red::Column @.columns; method returns { Nil } method args { |@!columns } method find-column-name {} } #| Represents an unique constraint class Red::AST::Unique is Red::AST::Constraint {} #| Represents a primary key constraint class Red::AST::Pk is Red::AST::Constraint {}