I appreciate the pun in that paper: Algebraic Data Types (ADTs) and pattern matching in functional languages lay a fertile ground to conveniently define an

I appreciate the pun in that paper: Algebraic Data Types (ADTs) and pattern matching in functional languages lay a fertile ground to conveniently define and process data types as tree-like structures. However, in these grounds, trees often cannot grow; once a data type is defined and compiled, its definition cannot be extended.