1.2. Data types

Erlang provides the following data types:

• Constant data types – these are data types which cannot be split into more primitive subtypes:
  • Numbers – for example: 123, -789, 3.14159, 7.8e12, -1.2e-45. Numbers are further subdivided into integers and floats.
  • Atoms – for example: abc, 'An atom with spaces', monday, green, hello_world. These are simply constants with names.
• Compound data types – these are used to group together other data types. There are two compound data types:
  • Tuples – for example: {a, 12, b}, {}, {1, 2, 3}, {a, b, c, d, e}. Tuples are used for storing a fixed number of items and are written as sequences of items enclosed in curly brackets. Tuples are similar to records or structures in conventional programming languages.
  • Lists – for example: [], [a, b, 12], [22], [a, 'hello friend']. Lists are used for storing a variable number of items and are written as sequences of items enclosed in square brackets.

Components of tuples and lists can themselves be any Erlang data item – this allows us to create arbitrary complex structures.

The values of Erlang data types can be stored in variables. Variables always start with an upper-case letter so, for example, the code fragment:

X = {book, preface, acknowledgments, contents,
     {chapters, [
        {chapter, 1, 'An Erlang Tutorial'},
        {chapter, 2, ...}
        ]
    }},

creates a complex data structure and stores it in the variable X.