Functions

Functions let us give a name to a sequence of instructions and use it more than once. We have already used the special main function. Ordinary functions use the same syntax:

namespace Greetings

function greet(name: String)
    print("Hello")
    print(name)
end

function main()
    greet("Ada")
    greet("Linus")
end

The name: String parameter says that greet needs one string. A call supplies that value between parentheses.

Returning a value

Write the result type after the parameter list, then use return to send a value back to the caller:

function double(number: Int): Int
    return number * 2
end

Calling double(6) produces the value 12:

local answer = double(6)
print(answer)

Pop checks both sides of the function boundary. Each argument must match its parameter type, and every returned value must match the declared result type.

Unlike local variables, a function result is not inferred. If the declaration has no result annotation, the function returns no value. Use : Int, : String, or another type whenever callers need a result.

More than one parameter

Separate parameters and arguments with commas:

function add(left: Int, right: Int): Int
    return left + right
end

local total = add(20, 22)

Arguments are matched by position: 20 becomes left, and 22 becomes right.

Returning from a decision

A result-producing function must return on every path that can reach its end:

function larger(left: Int, right: Int): Int
    if left > right then
        return left
    else
        return right
    end
end

Removing the else branch would leave a path with no result when left is not greater than right, so Pop rejects that version.

Visibility

Functions without a visibility word are available within their current Bubble. Add public when code in another Bubble should be able to call one:

public function add(left: Int, right: Int): Int
    return left + right
end

The Modules and Packages part explains public, internal, and private in context. While learning, an omitted visibility is usually all you need.