lux/docs/guide/09-stdlib.md

Chapter 9: Standard Library

Lux comes with a comprehensive standard library. This chapter covers the built-in modules.

Built-in Functions

Always available, no import needed:

toString(42)        // "42" - convert any value to string
typeOf(42)          // "Int" - get type name
print("hello")      // Print to console (shortcut)

List Module

Operations on lists:

let nums = [1, 2, 3, 4, 5]

// Transformations
List.map(nums, fn(x: Int): Int => x * 2)     // [2, 4, 6, 8, 10]
List.filter(nums, fn(x: Int): Bool => x > 2) // [3, 4, 5]
List.fold(nums, 0, fn(acc: Int, x: Int): Int => acc + x)  // 15

// Access
List.head(nums)      // Some(1)
List.tail(nums)      // [2, 3, 4, 5]
List.get(nums, 2)    // Some(3)
List.length(nums)    // 5
List.isEmpty([])     // true

// Building
List.range(1, 5)     // [1, 2, 3, 4]
List.concat([1,2], [3,4])  // [1, 2, 3, 4]
List.reverse(nums)   // [5, 4, 3, 2, 1]

// Searching
List.find(nums, fn(x: Int): Bool => x > 3)  // Some(4)
List.any(nums, fn(x: Int): Bool => x > 3)   // true
List.all(nums, fn(x: Int): Bool => x > 0)   // true

// Slicing
List.take(nums, 3)   // [1, 2, 3]
List.drop(nums, 3)   // [4, 5]

String Module

String manipulation:

let s = "Hello, World!"

// Info
String.length(s)           // 13
String.isEmpty("")         // true

// Search
String.contains(s, "World")     // true
String.startsWith(s, "Hello")   // true
String.endsWith(s, "!")         // true

// Transform
String.toUpper(s)          // "HELLO, WORLD!"
String.toLower(s)          // "hello, world!"
String.trim("  hi  ")      // "hi"
String.replace(s, "World", "Lux")  // "Hello, Lux!"

// Split/Join
String.split("a,b,c", ",")      // ["a", "b", "c"]
String.join(["a","b","c"], "-") // "a-b-c"
String.lines("a\nb\nc")         // ["a", "b", "c"]
String.chars("abc")             // ["a", "b", "c"]

// Substring
String.substring(s, 0, 5)  // "Hello"

Option Module

Working with optional values:

let some = Some(42)
let none: Option<Int> = None

// Check
Option.isSome(some)    // true
Option.isNone(none)    // true

// Transform
Option.map(some, fn(x: Int): Int => x * 2)  // Some(84)
Option.flatMap(some, fn(x: Int): Option<Int> => Some(x + 1))  // Some(43)

// Extract
Option.getOrElse(some, 0)   // 42
Option.getOrElse(none, 0)   // 0

Result Module

Working with results:

let ok: Result<Int, String> = Ok(42)
let err: Result<Int, String> = Err("oops")

// Check
Result.isOk(ok)     // true
Result.isErr(err)   // true

// Transform
Result.map(ok, fn(x: Int): Int => x * 2)      // Ok(84)
Result.mapErr(err, fn(e: String): String => "Error: " + e)  // Err("Error: oops")
Result.flatMap(ok, fn(x: Int): Result<Int, String> => Ok(x + 1))  // Ok(43)

// Extract
Result.getOrElse(ok, 0)    // 42
Result.getOrElse(err, 0)   // 0

Math Module

Mathematical functions:

Math.abs(-5)        // 5
Math.min(3, 7)      // 3
Math.max(3, 7)      // 7
Math.pow(2, 10)     // 1024
Math.sqrt(16)       // 4.0
Math.floor(3.7)     // 3
Math.ceil(3.2)      // 4
Math.round(3.5)     // 4

Json Module

JSON parsing and generation:

// Parse JSON string
let data = Json.parse("{\"name\": \"Alice\", \"age\": 30}")

// Access fields
Json.get(data, "name")     // Some("Alice")
Json.getInt(data, "age")   // Some(30)

// Create JSON
let obj = Json.object([
    ("name", Json.string("Bob")),
    ("age", Json.int(25))
])

// Convert to string
Json.stringify(obj)        // "{\"name\":\"Bob\",\"age\":25}"
Json.prettyPrint(obj)      // Formatted with indentation

Standard Library Modules (std/)

Import from the std/ directory:

std/prelude

import std/prelude.*

identity(42)         // 42
compose(f, g)        // Function composition
flip(f)              // Flip argument order
not(true)            // false
and(true, false)     // false
or(true, false)      // true

std/io

import std/io

io.println("Hello")          // Print with newline
io.print("No newline")       // Print without newline
io.readLine()                // Read line from input
io.debug("label", value)     // Debug print, returns value

std/option

import std/option as opt

opt.some(42)                 // Some(42)
opt.none()                   // None
opt.map(x, f)                // Map function over option
opt.flatMap(x, f)            // FlatMap
opt.filter(x, pred)          // Filter by predicate
opt.toList(x)                // Convert to list

std/result

import std/result as res

res.ok(42)                   // Ok(42)
res.err("oops")              // Err("oops")
res.mapOk(r, f)              // Map over Ok value
res.mapErr(r, f)             // Map over Err value
res.unwrapOr(r, default)     // Get value or default

Built-in Effects

Console

fn example(): Unit with {Console} = {
    Console.print("Hello")           // Print string
    let line = Console.readLine()    // Read line
    let num = Console.readInt()      // Read integer
}

File

fn example(): Unit with {File} = {
    let content = File.read("file.txt")        // Read file
    File.write("out.txt", "content")           // Write file
    let exists = File.exists("file.txt")       // Check existence
    let files = File.list("./dir")             // List directory
    File.mkdir("newdir")                       // Create directory
    File.delete("file.txt")                    // Delete file
}

Process

fn example(): Unit with {Process} = {
    let output = Process.exec("ls", ["-la"])   // Run command
    let home = Process.env("HOME")             // Get env var
    let args = Process.args()                  // Get CLI args
    let cwd = Process.cwd()                    // Current directory
    Process.exit(0)                            // Exit program
}

Http

fn example(): Unit with {Http} = {
    let body = Http.get("https://api.example.com/data")
    let response = Http.post("https://api.example.com/data", jsonBody)
    Http.put("https://api.example.com/data/1", updatedBody)
    Http.delete("https://api.example.com/data/1")
}

Random

fn example(): Unit with {Random} = {
    let n = Random.int(1, 100)     // Random int in range
    let f = Random.float()          // Random float 0.0-1.0
    let b = Random.bool()           // Random boolean
}

State

fn example(): Int with {State} = {
    let current = State.get()       // Get current state
    State.put(current + 1)          // Update state
    State.get()
}

// Initialize with value
run example() with { State = 0 }

Fail

fn example(): Int with {Fail} = {
    if condition then Fail.fail("Error message")
    else 42
}

Quick Reference

Module	Key Functions
List	map, filter, fold, head, tail, length, concat
String	split, join, trim, contains, replace, toUpper
Option	map, flatMap, getOrElse, isSome, isNone
Result	map, mapErr, flatMap, getOrElse, isOk
Math	abs, min, max, pow, sqrt, floor, ceil
Json	parse, stringify, get, object, array

Effect	Operations
Console	print, readLine, readInt
File	read, write, exists, list, mkdir, delete
Process	exec, env, args, cwd, exit
Http	get, post, put, delete
Random	int, float, bool
State	get, put
Fail	fail

Next

Chapter 10: Advanced Topics - Traits, generics, and optimization.