Strings and Format Strings

Table of contents
  1. Basic strings
  2. Strings with quotes inside
  3. Escape sequences
  4. String operations
    1. Combining strings
    2. Checking if text contains something
  5. Format strings - The powerful way
    1. Embedding calculations
    2. Multiple values
    3. Complex expressions
  6. Literal braces
  7. Practical examples
    1. User notifications
    2. Email subject lines
    3. Status messages
    4. Log messages
  8. Unicode support
  9. Try it yourself!

Numbers are great, but most programs need to work with text too. In Melbi, text values are called strings.

Basic strings

Create a string by wrapping text in double quotes:

"Hello, world!"

Or single quotes:

'Hello, world!'

Both work the same way. Use whichever you prefer (or whichever lets you avoid escaping quotes inside your string).

Strings with quotes inside

If your string contains quotes, you have two options:

Use the other kind of quote:

"It's a beautiful day"

'She said "Hello!"'

Or escape them with a backslash:

"She said \"Hello!\""

'It\'s a beautiful day'

Escape sequences

Use backslashes to include special characters:

"Line 1\nLine 2"

This creates a string with a newline between the two lines.

Common escape sequences:

  • \n - newline
  • \t - tab
  • \\ - backslash itself
  • \" - double quote
  • \' - single quote
  • \0 - null character

String operations

Combining strings

This feature is not available yet, but is planned.

In the future, you’ll be able to combine strings with an operator (likely ++):

"Hello, " ++ "world!"

For now, use format strings to combine text:

f"{ greeting }{ name }" where {
    greeting = "Hello, ",
    name = "Bob",
}

Checking if text contains something 

"hello" in "hello world"

This evaluates to true - “hello” is found in “hello world”.

"goodbye" in "hello world"

This is false - “goodbye” is not in that string.

The in operator is perfect for checking if an email contains certain words, if a filename has an extension, or if a message contains profanity.

Format strings - The powerful way

Instead of manually concatenating strings, use format strings. They start with f and let you embed expressions directly:

f"Hello { name }!" where { name = "Alice" }

This evaluates to: "Hello Alice!"

The part in curly braces {name} is replaced with the value of name.

Embedding calculations

You can put any expression inside the braces:

f"2 + 2 = { 2 + 2 }"

Result: "2 + 2 = 4"

f"The total is ${ price * quantity }" where {
    price = 29.99,
    quantity = 3,
}

Result: "The total is $89.97"

Multiple values 

f"{ greeting }, { name }! You have { count } new messages." where {
    greeting = "Hello",
    name = "Alice",
    count = 5,
}

Result: "Hello, Alice! You have 5 new messages."

Complex expressions 

f"Your score is { score * 100 }%" where { score = 0.95 }

f"Tax: ${ price * tax_rate }" where {
    price = 100,
    tax_rate = 0.08,
}

Literal braces

What if you need actual curly braces in your string? Use double braces:

f"Use  like this"

Result: "Use {curly braces} like this"

Practical examples

User notifications 

f"Hi { user }! Your order #{ order_id } will arrive on { delivery_date }." where {
    user = "John",
    order_id = 12345,
    delivery_date = "Monday",
}

Email subject lines 

f"[{ status }] Ticket #{ ticket }: { title }" where {
    status = "RESOLVED",
    ticket = 4567,
    title = "Login issue",
}

Status messages 

f"Processing { current } of { total } items ({ percentage }% complete)" where {
    current = 7,
    total = 10,
    percentage = (current * 100) / total,
}

Log messages 

f"{ timestamp } - { level }: { message }" where {
    timestamp = "2024-11-23 10:30:00",
    level = "ERROR",
    message = "Connection timeout",
}

Unicode support

Melbi strings fully support Unicode, so you can use emoji, accented characters, and text from any language:

"Hello 世界! 🌍"

"café"

f"Math: π ≈ { pi }" where { pi = 3.14159 }

Try it yourself!

Create expressions that:

  1. Build a full name from first and last name
  2. Create an email address from username and domain
  3. Format a price with dollar sign and two decimal places
  4. Build a welcome message with someone’s name and the time of day
  5. Create a filename with a timestamp

In the next lesson, you’ll learn how to make decisions with conditionals!