B.13 Thematic Takeaways

• While a goal of the functional style of programming is to bring programming closer to mathematics, ML and its syntax, as well as the responses of the ML interpreter (particularly for tuples and functions), make the connection between functional programming and mathematics salient.

• Native support for pattern-directed invocation is one of the most convenient features of user-defined functions in ML because it obviates the need for an if–then–else expression to differentiate between the various inputs to a function.

• Use of pattern-directed invocation (i.e., pattern matching) introduces declarative programming into ML.

• Pattern-directed invocation is not operator/function overloading.

• Operator/function overloading (sometimes called ad hoc polymorphism) is not parametric polymorphism.