Function

A function is used to combine a sequence of statements so that it may be called multiple times throughout a program. Functions also allow names to be given to sections of code, improving readability. Here is an example:

function fizzbuzz? (number) {
  divisibleBy3 = number % 3 == 0;
  divisibleBy5 = number % 5 == 0;

  return divisibleBy3 && divisibleBy5;
};

The following sections explain how functions are defined and called in Sentient. These sections get progressively more complicated but you should be able to glean the basics without understanding all of its intricacy.

Defining functions

Functions can be defined anywhere in a program, including inside other functions. All function names are global and if a function definition appears with the same name elsewhere, it will be redefined.

Function names can optionally be suffixed with a single ? or ! character. Functions can take any number of arguments and can return any number of values. Here is an example:

function payForGoods (cost, balance) {
  balance -= cost;
  overdrawn = balance < 0;

  return balance, overdrawn;
};

If a function returns values, its return statement must appear as the last statement in a function.

Variable scope

By default, functions have local scope and cannot access variables from outside. Functions are pass-by-value, which means that a copy is made of the function’s arguments when they are passed in.

It is possible to define functions that can access variables outside by using the ^ modifier. The following example updates the balance variable, which appears outside of the defined function:

balance = 1000;

function^ payForGoods (cost) {
  balance -= cost;
  overdrawn = balance < 0;

  return overdrawn;
};

If functions are nested, the ^ modified will not provide access to variables outside of the outermost function unless that also uses the ^ modifier.

Calling functions

Functions are called by passing arguments within parentheses. You can either call functions as part of an assignment or in a statement on their own. This is to support cases where functions have side-effects such as this example:

payForGoods(50);

When functions return more than one value, you can use multiple assignment to set those values to variables:

div, mod = divmod(10, 3);

Method syntax

It is also possible to call functions using a method syntax. Any function can be called on any value and that value will be passed as the first argument to the function. Here is an example:

div, mod = 10.divmod(3);

When functions are called as methods, the parentheses are optional unless there are additional arguments, for example:

a = 75.fizzbuzz?;

In fact, almost all syntax in the language is described as method calls on values which means that these are all equivalent:

a = 2 + 2;
a = +(2, 2);
a = 2.+(2);

Function pointers

It is possible to pass functions as arguments to other functions using function pointers. You can pass any number of pointers to a function. A function pointer is denoted by prefixing a * to an argument:

function callTwice (x, *f) {
  return f(f(x));
};

function double (x) {
  return x * 2;
};

a = 5.callTwice(*double);

Sentient also supports anonymous functions, which can be passed in to other functions. Here is an example that adds the numbers in an array:

array5<int> numbers;
total = 0;

numbers.each(function^ (number) {
  total += number;
});

expose numbers, total;