Arrays

Table of contents
  1. Your first array
  2. Empty arrays
  3. Accessing elements
  4. Using with where bindings
  5. Arrays of any type
    1. Numbers
    2. Strings
    3. Booleans
    4. Mixed? No!
  6. Nested arrays
  7. Practical examples
    1. Test scores
    2. Email list
    3. Days of the week
    4. Color palettes
  8. Array expressions
  9. Using the in operator
  10. Real-world examples
    1. Menu selection
    2. Price tiers
    3. Status codes
    4. Coordinates
  11. Important notes
  12. Try it yourself!

So far you’ve worked with single values - one number, one string, one boolean. But what if you need to work with a collection of values? That’s where arrays come in!

Your first array

An array is a list of values wrapped in square brackets:

[1, 2, 3, 4, 5]

["apple", "banana", "cherry"]

[true, false, true]

That’s it! You now have a collection of values.

Empty arrays

You can create an empty array with just the brackets:

[]

This is useful as a starting point or to represent “no items.”

Accessing elements

Get individual elements using their position (index). Arrays start counting at 0:

fruits[0] where { fruits = ["apple", "banana", "cherry"] }

This gives you "apple" - the first element.

fruits[1] where { fruits = ["apple", "banana", "cherry"] }

This gives you "banana" - the second element.

fruits[2] where { fruits = ["apple", "banana", "cherry"] }

This gives you "cherry" - the third element.

Remember: computers start counting at 0, so the first element is at index 0!

Using with where bindings

Arrays work great with where bindings:

best_score where {
    scores = [95, 87, 92, 78, 88],
    best_score = scores[0],
}

message where {
    names = ["Alice", "Bob", "Charlie"],
    first = names[0],
    last = names[2],
    message = f"{ first } and { last } are here",
}

Arrays of any type

Arrays can hold numbers, strings, booleans, or even other arrays!

Numbers 

[1, 2, 3, 4, 5]

[3.14, 2.71, 1.41]

Strings 

["red", "green", "blue"]

["user@example.com", "admin@site.com"]

Booleans 

[true, false, true, true]

Mixed? No!

Here’s an important rule: all elements in an array must be the same type. You can’t mix numbers and strings:

[1, "two", 3]

This would give an error. Melbi is strict about types to catch mistakes early!

Nested arrays

Arrays can contain other arrays:

[[1, 2], [3, 4], [5, 6]]

Access nested elements with multiple brackets:

grid[0][1] where {
    grid = [[1, 2], [3, 4], [5, 6]],
}

This gives you 2 - the second element of the first array.

Think of it like a spreadsheet - grid[0] gets you the first row, then [1] gets you the second column.

Practical examples

Test scores 

average where {
    scores = [95, 87, 92, 78, 88],
    total = scores[0] + scores[1] + scores[2] + scores[3] + scores[4],
    count = 5,
    average = total / count,
}

Email list 

f"Sending to: { emails[0] }, { emails[1] }, and { emails[2] }" where {
    emails = ["alice@example.com", "bob@example.com", "charlie@example.com"],
}

Days of the week 

today where {
    days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"],
    day_index = 3,
    today = days[day_index],
}

Color palettes 

primary_color where {
    palette = ["#FF5733", "#33FF57", "#3357FF", "#F333FF"],
    primary_color = palette[0],
}

Array expressions

You can build arrays using expressions:

[1 + 1, 2 * 2, 3 - 1]

This evaluates to [2, 4, 2].

[price * 1.1, price * 0.9] where { price = 100 }

This gives you [110.0, 90.0] - 10% above and below the price.

Using the in operator

Check if a value exists in an array:

5 in [1, 2, 3, 4, 5]

This is true - 5 is in the array.

"cat" in ["dog", "bird", "fish"]

This is false - “cat” is not in that array.

Perfect for checking permissions, valid options, or blacklists:

if role in admin_roles then "Access granted" else "Access denied"
where {
    role = "moderator",
    admin_roles = ["admin", "super_admin", "moderator"],
}

if extension in allowed then "Upload accepted" else "Invalid file type"
where {
    extension = ".jpg",
    allowed = [".jpg", ".png", ".gif", ".webp"],
}

Real-world examples 

selected_item where {
    menu = ["New", "Open", "Save", "Exit"],
    choice = 2,
    selected_item = menu[choice],
}

Price tiers 

price where {
    tiers = [9.99, 19.99, 49.99, 99.99],
    tier_index = 1,
    price = tiers[tier_index],
}

Status codes 

is_success where {
    success_codes = [200, 201, 204],
    response_code = 200,
    is_success = response_code in success_codes,
}

Coordinates 

distance where {
    point1 = [0, 0],
    point2 = [3, 4],
    dx = point2[0] - point1[0],
    dy = point2[1] - point1[1],
    distance = (dx ^ 2 + dy ^ 2) ^ 0.5,
}

Important notes

  1. Arrays are zero-indexed - the first element is at position 0
  2. All elements must be the same type - no mixing numbers and strings
  3. Arrays are immutable - you can’t change them after creation (but you can create new ones!)
  4. Accessing an index that doesn’t exist gives an error - but you can handle these errors gracefully with otherwise (you’ll learn how later!)

Try it yourself!

Create expressions that:

  1. Store the RGB values for a color and calculate the average
  2. Create a shopping list and check if an item is in it
  3. Store coordinates for a route and calculate distances
  4. Make an array of prices and find the most expensive (hint: compare them!)
  5. Build a tic-tac-toe board using nested arrays

In the next lesson, you’ll learn about records - a way to group related values with names!