Functions

A method that returns a value, and the rules that keep you from forgetting one.

So far every program of yours fits inside start, and the only way to get a result out is to print it. A method acts; it returns nothing.

This section teaches it to return a value — and lays down the two rules that come with it: a return type binds every path, and a statement that does nothing is refused. It ends with parameters you are allowed to leave out.

In this section

• 5.1Returning a value

  An arrow, a return, and a call stops being a mere action to become a value.

• 5.2Every path must return

  A method that announces a return type must honour it everywhere, and the three ways to forget a path.

• 5.3Only a call stands alone

  A statement that computes a value and throws it away is refused — and that refusal closes the last shape of the = trap.

• 5.4Default values

  A parameter that may be left out, and the value it takes when nothing is said.