Constants

Constants are immutable values known at compile time.

Declaration

const MAX_CONNECTIONS = 1000
const APP_VERSION = "1.4.0"
const DEBUG_MODE = false

Constant Expressions

Constants can be assigned from constant expressions:

const BASE_URL = "https://api.example.com"
const API_PATH = "/v1"
const FULL_URL = BASE_URL + API_PATH

Type Annotations

Type annotations are optional but recommended for clarity:

const TIMEOUT: Int = 30
const MAX_RETRIES: Int = 3
const DEFAULT_NAME: String = "anonymous"

Module-Level Constants

Constants are typically declared at the module level:

const PI = 3.14159265358979
const E = 2.71828182845905

action circle_area(@radius: Float) -> Float
    return PI * @radius * @radius
fin action.

Scoped Constants

Constants can be defined inside actions:

action process()
    const LOCAL_LIMIT = 50
    for @i in 0..LOCAL_LIMIT
        process_item(@i)
    fin for.
fin action.

Enum Constants

Enums define a set of named constants:

enum Color
    Red
    Green
    Blue
fin enum.

@// Usage
@primary = Color#Red

See Enums for full details.

Constant vs Variable

Feature	Variable (@)	Constant (const)
Mutability	Mutable with mut	Always immutable
Assignment	Runtime	Compile time
Scope	Block or module	Block or module
Type inference	Yes	Yes
Shadowing	Yes	No

Naming Convention

Constants use CONSTANT_CASE (uppercase with underscores):

const MAX_BUFFER_SIZE = 8192
const DEFAULT_TIMEOUT_MS = 5000
const ENABLE_LOGGING = true

Importing Constants

Constants can be imported from other modules:

import { MAX_RETRIES, API_KEY } from config

action connect()
    for @i in 0..MAX_RETRIES
        if try_connect()
            return true
        fin if.
    fin for.
    return false
fin action.

Compile-Time Evaluation

Constants are evaluated at compile time, enabling optimizations:

const SIZE = 1024 * 1024    @// Computed at compile time
const FLAGS = 0x01 | 0x02   @// Bitwise operations allowed

Expressions in constants must be determinable at compile time. Function calls are not allowed unless they are const functions (future feature).

Next Steps

Learn about Types to understand Draft’s type system.