> then what language features in any language be good? Those that obey general principles without exception. For example: (0) “Abstraction clients must not re

> then what language features in any language be good? Those that obey general principles without exception. For example: (0) “Abstraction clients must not rely on implementation details”: parametric polymorphism, abstract data types. (1) “Case analyses must be exhaustive”: algebraic data types and pattern matching. (2) “Make as few assumptions possible about the intended meaning of programs”: principal types.