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User-defined functions

Everything we did with functions so far was about the fixed set of built-ins. A real language lets the user create their own functions, and this is what we implement in the rest of this chapter. As always, let us first design the syntax:

func add(a, b) {
    return a + b;
}
say add(3, 4);

A function is introduced by the func keyword, followed by a name, a comma-separated list of parameters in parentheses, and a body in curly braces. Unlike the built-in functions, which are called without parentheses, a user-defined function is called with its arguments in parentheses. Keeping the two syntaxes different is not only simpler to parse. It also lets the reader of a program immediately see whether a function is a part of the language or a part of the program.

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