Built-in Functions

These functions are available globally in every .jo program.

print(value, ...)

Prints one or more values to standard output, separated by spaces, followed by a newline.

print("Hello")               // Hello
print("Load:", 72, "%")      // Load: 72 %
print(192.168.1.1)           // 192.168.1.1

len(value)

Returns the length of a String (character count), List (element count), or Map (key count).

len("hello")         // 5
len([1, 2, 3])       // 3
len({a: 1, b: 2})    // 2

type(value)

Returns the type name of a value as a String.

type(42)             // "Integer"
type(3.14)           // "Float"
type("hi")           // "String"
type(true)           // "Bool"
type(null)           // "Null"
type([1, 2])         // "List"
type({})             // "Map"
type(10.0.0.0/8)     // "Subnet"
type(192.168.1.1)    // "IP"

str(value)

Converts any value to its String representation.

str(100)             // "100"
str(3.14)            // "3.14"
str(true)            // "true"
str(null)            // "null"
str(192.168.1.1)     // "192.168.1.1"

int(value)

Converts a Float or numeric String to an Integer.

int(3.9)             // 3  (truncates)
int("42")            // 42

float(value)

Converts an Integer or numeric String to a Float.

float(7)             // 7.0
float("3.14")        // 3.14

range(stop) / range(start, stop) / range(start, stop, step)

Generates a List of integers. Mirrors Python’s range().

range(5)             // [0, 1, 2, 3, 4]
range(2, 6)          // [2, 3, 4, 5]
range(0, 10, 2)      // [0, 2, 4, 6, 8]
range(5, 0, -1)      // [5, 4, 3, 2, 1]

abs(n)

Returns the absolute value of a number.

abs(-7)    // 7
abs(3.5)   // 3.5

max(a, b, ...) / min(a, b, ...)

Returns the largest or smallest value among the arguments.

max(3, 7, 2)   // 7
min(3, 7, 2)   // 2

sqrt(n)

Returns the square root of n as a Float.

sqrt(16)    // 4.0
sqrt(2)     // 1.4142135...

pow(base, exp)

Returns base ** exp as a Float.

pow(2, 10)   // 1024.0
pow(3, 3)    // 27.0

floor(n) / ceil(n) / round(n)

Standard rounding functions. floor and ceil return an Integer; round returns an Integer.

floor(3.9)   // 3
ceil(3.1)    // 4
round(3.5)   // 4
round(3.4)   // 3

input(prompt?)

Reads a line from standard input and returns it as a String. An optional prompt string is printed before reading.

let name = input("Enter your name: ")
print("Hello, " + name)

assert(condition, message?)

Asserts that condition is truthy. If it is not, a Runtime Error is raised with the optional message.

assert(1 + 1 == 2)
assert(len("hello") == 5, "String length is wrong")

// Failure:
assert(false, "This always fails")
// ❌ Runtime Error: This always fails

format(template, args...)

Returns a formatted string by replacing each {} placeholder with the corresponding argument (converted via str()).

let msg = format("Hello, {}! You are {} years old.", "Alice", 30)
print(msg)   // Hello, Alice! You are 30 years old.

let log = format("[{}] ERROR: {}", "2026-01-01", "Disk full")
print(log)   // [2026-01-01] ERROR: Disk full

Placeholders are filled left-to-right. Extra arguments are ignored; unmatched {} remain as-is.

quarantine(ip)

Prints a quarantine notice and returns true. This is a simulation; it does not isolate a host or change firewall rules.

quarantine(suspicious_ip)
// [SECURITY] Quarantining: 10.0.0.99

trigger_alert(location:)

Prints an alert notice and returns null. No external alert is sent. Named labels such as location: are accepted by the parser, but arguments are passed positionally; labels do not reorder arguments.

trigger_alert(location: "Server Room B")
// [ALERT] Server Room B