A locally defined function can have 0 or 1 arguments. All basic
types can be sent in the argument. A return value is sent with the
'return' statement. All four types can be used in the return statement.
The type of the function must no be declared.
The type of the argument must not be declared. It is illegal to have a
function with the same name as a global function, or local variable.
The function is reentrant.

function_name(argument_name) {
    statements;
    ...
    return value;
}