Global Constants

Define values at the module level that can be accessed anywhere in your code.

Basic Syntax

let MAX_USERS = 100
let APP_NAME = "MyApp"
let PI = 3.14159
let DEBUG = true

def main() -> int:
    print(f"App: {APP_NAME}")
    print(f"Max: {MAX_USERS}")
    return 0

Naming Convention

Use UPPER_CASE for globals:

# ✓ Good
let MAX_SIZE = 1024
let API_KEY = "secret"

# ✗ Warning
let myConst = 42  # Warning: should be UPPER_CASE

Underscore prefixes are also valid:

let _INTERNAL_VALUE = 99  # No warning - underscore prefix allowed

Immutability

Globals are always immutable:

# ✓ Correct
let VERSION = "1.0.0"

# ✗ Error
let mut counter = 0  # Error: global must be immutable

Visibility

Only pub globals can be imported:

# config.desi
pub let MAX_RETRIES = 3   # Exported
let INTERNAL_KEY = "abc"  # Private
let _SECRET = "hidden"    # Private (underscore convention)

# main.desi
from config import MAX_RETRIES  # Works
from config import INTERNAL_KEY # Error: not public

Either import form reaches an exported constant:

from config import MAX_RETRIES
print(str(MAX_RETRIES))

import config
print(str(config.MAX_RETRIES))

Supported Types

# Integers
let INT_VAL = 42
let NEG_VAL = -100

# Floats
let FLOAT_VAL = 3.14

# Booleans
let BOOL_VAL = true

# Strings
let STR_VAL = "Hello"

Computed Values

An initializer may be arithmetic over numeric literals, or + over string literals. It is folded at compile time, so the constant is usable from other modules like any other:

let SECONDS_PER_DAY = 60 * 60 * 24   # 86400
let TIMEOUT_MS: int = 30 * 1000      # 30000
let AREA = (2 + 3) * 10              # 50
let RATIO = 1.5 * 2.0                # 3.0
let BANNER = "desi " + "0.1.0"       # "desi 0.1.0"

Anything that has to run to produce its value — a function call, a constructor — is not a constant expression:

let LIMIT = compute_limit()   # Not a constant

Call the function where you use it

A global initialized by a function call is only initialized when the module that declares it runs. Importing such a constant does not run it, and the link fails with an undefined symbol. Put the call in a function and call it from main, or write the value out as a literal.

Using in F-Strings

let APP_NAME = "Desi"
pub let VERSION = "0.1.0"
let _BUILD = 123

def main() -> int:
    print(f"{APP_NAME} v{VERSION} (build {_BUILD})")
    return 0

Best Practices

Do	Don't
Use for configuration	Use for mutable state
Keep values simple	Define complex objects
Use pub for exported values	Assume visibility
Use UPPER_CASE or _UPPER_CASE	Use camelCase