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Variables and Values

Understanding Draft's variable system, types, and mutability.

Variables and Values

Draft uses an explicit variable declaration system with @ prefixed identifiers. This tutorial covers variable assignment, type inference, and mutability.

Declaring Variables

Variables in Draft are declared with the @ prefix and assigned with =.

action main()
    @name = "Draft"
    @version = 0.1
    @count = 42
fin action.

Draft infers the type of each variable from its initial value. You do not need to write type annotations unless you want to.

Types

Draft has a small set of built-in types:

Type Example Description
int 42 Signed integer
float 3.14 Floating-point number
str "hello" UTF-8 string
bool true Boolean
list [1, 2, 3] Ordered collection
map {"a": 1} Key-value mapping
void null Empty value

Type Inference

The compiler infers types from literals and expressions:

action main()
    @x = 10          // int
    @y = 3.14        // float
    @greeting = "hi" // str
    @active = true   // bool
fin action.

You can also write explicit types when needed:

action main()
    @score: int = 0
    @ratio: float = 1.5
    @name: str = "player"
fin action.

Mutability

Variables are immutable by default. Use mut to declare a mutable variable.

action main()
    @score = 0        // immutable
    @mut level = 1    // mutable


    level = level + 1 // allowed
    // score = 10     // error: score is immutable
fin action.

Immutable variables help catch bugs at compile time and allow the compiler to optimize more aggressively.

Member Access

Access fields and methods with #:

action main()
    @user = {"name": "Ada", "score": 100}
    write(user#name)   // prints: Ada
    write(user#score)  // prints: 100
fin action.

Strings and Interpolation

Concatenate strings with + or use interpolation:

action main()
    @name = "Draft"
    @message = "Hello, " + name + "!"
    write(message) // prints: Hello, Draft!
fin action.

Lists

Create lists with square brackets:

action main()
    @numbers = [1, 2, 3, 4, 5]
    @first = numbers[0]
    @last = numbers[-1]
    write(first) // prints: 1
    write(last)  // prints: 5
fin action.

Best Practices

  • Prefer immutable variables unless mutation is required
  • Let the compiler infer types in simple cases
  • Use descriptive variable names

Next Steps