Chapter 18. Types and Documentation

The basic types in Erlang—integers, floating-point numbers, atoms, strings, tuples, and lists—were introduced in Chapter 2; records were covered in Chapter 7; and further types—binaries and references—in Chapter 9. When we have declared functions and other definitions, we have also given an informal description of the types of their inputs and outputs.

This chapter shows how you can write down the types of functions as a part of their formal documentation in Erlang, using the EDoc documentation framework, written by Richard Carlsson. What you write down as the type of a function can be checked for consistency against the function definition using the TypEr tool, built by the implementers of Dialyzer. TypEr will infer types without any user input, and so it can be an essential tool for program understanding. TypEr and Dialyzer are the result of the High Performance Erlang (HiPE) team’s research at Uppsala University. All of these tools are part of the standard Erlang distribution.