Like every other field, functional programming comes with its own jargon. This small glossary has the goal to make reading the book easier and also provide you with more understanding of the resources you will find online.
The number of parameters a function takes. The terms nullary, unary, binary, and ternary are also used to denote functions that take 0, 1, 2, and 3 parameters respectively. See also variadic as follows.
A function that returns another function. Chapter 1, Functions as First Class Citizens, further explain the concepts of higher-order functions as this is one of the foundations of functional programming.
Anything that affects the world outside the current function: changing ...