Functions

Functions are a way to avoid repeating blocks of code. They can be very helpful! We have actually already used several! Functions work similarly to how they work in math.

Calling a Function

We have already done this serveral times! Let me show you.

import stdlib::*;

define main() {
    println("Hello World");
}

Yes, that is a function call! We tell the language we want to “call” code from the function println. We are then “passing” in the arguments inside of those parenthese. We are passing a single argument, a strlit.

Other Ways to Pass Arguments

BCL doesn’t require you to use parenthese when calling a function unless you are passing several arguments.

Let me show you a few ways you can call a function.

import stdlib::*;
import math::*;

define main() {
    "Hello World".println();
    println "Hello Again";

    // a function from math.bcl
    // returns the smallest number from the 2 passed in
    10.min 12;
    10.min(12);
}

Function Returns

Some functions give you a value back after calling them, this is called a “return value”. Let me give you an example to try!

import stdlib::*;
import math::*;

define main() {
    x = min(10, 12); // storing the return value in x
    println(x);

    // showing how we can put expressions anywhere they
    // are accepted.
    println(min(22, 20));
}

Give it a try and see what output you get!

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Defining Your Own Functions

Functions can be defined by you too. Like before, we have already done this! |

Here is a simple example.

import stdlib::*;

// defining our function
define say_hi() {
    println("Hi!");
}

define main() {
    say_hi(); // calling our function
}

Using Arguments

When defining functions, you can ask the caller to pass in some data. Arguments are how we do this. They act as variables in side the function.

import stdlib::*;

// the function has two arguments
// x is an i32 (a whole, integer number)
// y is an i32 too
define add_numbers(x: i32, y: i32) {
    println(x + y);
}

define main() {
    add_numbers(10, 20); // calling our function
}

Note

Data is coppied into the function when called, you cannot modify variables that the caller has passed in, you are just given a copy of the data.

Returning Data

We can also give data back to the caller using the return statement.

import stdlib::*;

// the function has two arguments
// x is an i32 (a whole, integer number)
// y is an i32 too
define add_numbers(x: i32, y: i32) {
    return x+y;
}

define main() {
    result = add_numbers(10, 20); // calling our function
    println(result);
}

One important thing to note about return is the fact that it tells the function to immediately stop running while also giving back a value to the caller.

Let me give you an example.

import stdlib::*;

define add_numbers(x: i32, y: i32) {
    return x+y;

    println("I won't be run!");
}

Side Notes

Functions can be confusing for some. Which I can understand. It took me several months to learn how return works when I first started writing code. It is an important concept so do take the time to learn it!

And, do note, that functions will get slightly more complicated later on. Specifically when we learn about methods and generators. For now, don’t worry about those.