Quick Syntax Style Guide

Quickly learn what the BoxLang language offers.

This guide provides a quick overview of BoxLang syntax styles, intricacies, operators, and features. It aims to assist developers from other languages in their BoxLang development journey. BoxLang has been heavily inspired by many different languages, including Java, CFML, Groovy, Kotlin, Ruby, PHP, and more.

If you are a CFML developer, check out also our CFML Guide.

Dynamic & Loose Typing

BoxLang variables are dynamic and type-inferred. We try our best to infer which type you are trying to set for variables at compile-time, but they can completely change at runtime. You use the var keyword to specify a variable within functions or declare them inline if you are in a bxs or bxm script file.

File Types:

  • bx - A BoxLang class

  • bxs - A BoxLang scripting file

  • bxm - A BoxLang templating markup file

// Infered as 'String'
name = "boxlang"

// Inferred as Double
age = 1
// But I can redeclare it to a string if I need to
age = "one"

// Inferred as Double
isActive = false

// Inferred as Date
today = now()

// Use the `var` keyword to define function-local only variables
function test(){
  var name = "hello"

You can also add types to arguments within functions or omit them, and it will default to any, which means, well, anything:

function add( required numeric a, required numeric b, boolean print = false ){


As you can see, not only can we make arguments required or not, but we can also add default values to arguments. BoxLang does not allow method overrides since basically, every method can take an infinite nubmer of arguments, defined or even NOT defined.

We can also do type promotions and auto-casting from types that can be castable to other types. So, if we call our function like this:

// we auto cast 1 to numeric, "true" to boolean
add( "1", 345, "true" )

This is handy as we really really try to match your incoming data to functional arguments.

Any by default

If they are not specifically typed, all arguments and variable declarations are of any type. This means they will be inferred at runtime and can change from one type to another.

// Variables declared in a script are of any type and inferred
name = "luis"

function hello( name ){
    // argument name can be anything

Case Insensitive Functionality

Most things in BoxLang can be done with no case sensitivity by default. You can enable case sensitivity in many functions and components, but we try to be insensitive as much as possible :). Here are a few observations where access is case-insensitive by nature:

  • variable access in any scope

  • function calls, even to Java classes

  • function arguments, even on Java classes

  • class creation, even on Java classes

name = "luis"
// Name can be outputted in any case
println( "Hi, my name is #NamE#" )

// Even maps or arrays
myMap = { name : "luis", age : 12 }
println( "My name is #mymap.NAME# and my age is #mymap.age#" )

Internally we leverage a Key class that provides us with case insensitivity. Each map has a Key as the, well, key.

Expression Interpolation

BoxLang can interpret ANYTHING within # as an expression. This can be used for output, assignments, and much more.

"#now()# is a bif, and this #12 % 2# is a math expression, and more!"

Multi-Line Strings

You can declare multi-line strings by using the """ start and end operators. You can also use any interpolation in between.

myLargeContent = """

    How are you today #name#!

    This is a very nice email with merged data!

    Thanks for purchasing #item#!

mailService.send( myLargeContent )

Multi-Variable Assignments

BoxLang supports the concept of multi-variable declaration and assignments by just cascading variables using the = operator.

name = threadname = taskName = "I am Spartacus!"

This will create the 3 variables in the variables scope with the name "I am Spartacus!"

Switch Statements

The BoxLang switch statements can work on any literal but also on any expression

switch( expression ) {
    case value : case value2 :{

    default : nothing

Catch `any` exception

BoxLang allows you to catch any exception using our any operator

    .. funky code here
} catch( any e ){

    // We just caught every single exception known to man!


Multi-Catch Exceptions

In BoxLang you can catch multiple exceptions by using the pipe | operator. They can be both BoxLang exceptions or Java exception types:

catch( foo.com | brad | com.luis.majano e ) {}

No Semicolons

As you can see, semicolons are completely optional. We prefer no semicolons unless you really, really need to demarcate a beginning and an end.


BoxLang offers many different persistence and variable scopes depending on where and what you are. All scopes in BoxLang are backed by the Map interface, which in BoxLang land are called Structures. They are case-insensitive by default; you can pass them around as much as you like.

Scripts (bxm, bxs)

Scripts can be written in full script (bxs) or using our templating language (bxm).

  • variables - Where all variables are stored

  • Unscoped variables go to the variables scope in a script


BoxLang supports all Object-oriented constructs know in several languages. We expand on the areas of metaprogramming and dynamic typing.

  • variables - The private scope of the class

  • this - The public scope of the class and also represents the instance

  • static - The same as Java, a static scope bound to the blueprint of the class

  • Unscoped variables go to the variables scope in a class


BoxLang supports 3 types of Functions.

  • local - A local scope available only to the function

  • arguments - The incoming arguments

  • variables - Access to the script or class private scope

  • this - Access to the class public scope

  • Unscoped variables go to the local scope in a function by default

Persistence Scopes

BoxLang and some of it's runtimes also offer out of the box scopes for persistence.

  • session - stored in server RAM or external storage tracked by a unique visitor

  • client - stored in cookies, databases, or external storages (simple values only)

  • application - stored in server RAM or external storage tracked by the running BoxLang application

  • cookie - stored in a visitor's browser (Web Only)

  • server - stored in server RAM for ANY application for that BoxLang instance

  • request - stored in RAM for a specific request ONLY

  • cgi - read-only scope provided by the servlet container and BoxLang (Web Only)

  • form - Variables submitted via HTTP posts (Web Only)

  • URL - Variables incoming via HTTP GET operations or the incoming URL (Web Only)

Please visit our scopes section to find out much more about scopes in BoxLang.

Scope Hunting

When you access a variable without specific scope access, BoxLang will try to find the variable for you in its nearest scope. This is done internally via a context object, which can be decorated at runtime depending on WHERE the code is being executed (CLI, web, lambda, android, etc) Example:

function( name ){

    // add to data, which has no scope and no arguments exist
    // so it looks for it in the variables scope
    data.append( name )

    // Looks in arguments first
    return name;

Check out our Scopes section to learn more about scope hunting.

Full Null Support

null is a real thing! It's nothing but real! We support the null keyword, assignments, and usage just like Java. It follows the same rules.

CastAs Operator

BoxLang has a natural casting operator that is fluent and readable.

myJavaClass( value castAs "long" )

return {
    age : value castAs "int",
    tags : value castAs "String[]",
    isActive : "#value#" castAs "Boolean"

You can also use our handy javaCast() bif if you needed to.

Human Operators

We have several fluent operators using english instead of symbols.

InstanceOf Operator

Like other languages, we also offer an instanceOf operator alongside a nice BIF: isInstanceOf(). You can also use negation using our lovely not operator.

isInstanceOf( obj, "Map" )

if( obj instanceOf "String" )
if( obj instanceOf "MyUser" )
if( obj not instanceOf "Integer" )

Data Types

All Java types can be used alongside the core BoxLang types:

  • any

  • array

  • immutableArray

  • binary

  • boolean

  • class

  • closure

  • date

  • double

  • guid

  • function

  • float

  • integer

  • lambda

  • numeric

  • number

  • query

  • string

  • struct

  • immutableStruct

  • uuid

Arrays are Human

Arrays in BoxLang start at 1, not 0. End of story!

Array/Struct Initializers

Arrays and Structs in BoxLang can be created using literal constructs. Please note that values within the literal declarations can also be expressions.

// empty array
array = []
// array with data
array = [ 1, 23, 234 ]

// empty struct
myMap = {}
// struct with data
myMap = { age:1, test: now() }


BoxLang Truthy and Falsey are concepts used in programming to determine the "truth" of a value in a Boolean context. In many programming languages, values other than true and false can be evaluated for their truthiness. Understanding truthy and falsey values is crucial for writing effective and accurate code when evaluating conditions or performing logical operations.

Truthy values

  • positive numbers (or strings which can be parsed as numbers)

  • boolean true

  • string “true”

  • string “yes”

  • array with at least one item

  • query with at least one row

  • struct with at least one key

Falsey values:

  • A null value

  • The number 0 or string “0”

  • boolean false

  • string “false”

  • string “no”

  • empty arrays

  • empty queries

  • empty structs

Imports & Class Locators

BoxLang offers the ability to import both BoxLang and Java classes natively into scripts or classes.

// Import java classes
import java:java.io.IOException
import java:java.nio.file.FileSystems
import java:java.nio.file.Path

// Import BoxLang classes
import models.User
import models.cborm.MyService

Works just like Java. However, you will notice a nice java: prefix. This is called an class locator prefix. BoxLang supports these out of the box:

  • java: - Java classes to import or instantiate

  • bx: - BoxLang classes to import or instantiate (Default, not required)

You can also remove the java: prefix and BoxLang will try to locate the class for you. Careful, as it will scan all locations.

Import Aliases

You can also alias imports to provide less ambiguity when dealing with classes with the same name:

// Import java classes
import java:java.nio.file.Path as jPath
import models.utils.Path

myJavaPath = new jPath()
myBxPath = new Path()

All the object resolvers prefixes can be used anywhere a class or path is expected:

  • Creating classes and instances: createObject(), new

  • Using imports

  • Extending classes

  • Implementing interfaces

class implements="java:java.util.List" {


class extends="java:ortus.boxlang.runtime.types.Struct"{


Null Coalescing aka Elvis Operator

BoxLang supports the null coalescing operator ?: to allow you to evaluate if values are empty or null. This is not a shortened ternary as other languages.

( expression ) ?: 'value or expression'

This tests the left-hand side of the ?: and if its null then it will evaluate the rigth expression or value. This can be used on if statements, assignments, loops, etc.

Safe Navigation Operator

BoxLang supports safety navigation on ANY object that can be dereferenced: structs, maps, classes, etc. This basically allows you to test if the value exists or not and continue dereferencing or return null

age = form.userdata?.age;

fullName = userClass?.getFullName()

Imagine how tedious this code is

if( order ){

    if( order.hasCustomer() ){
        if( order.getCustomer().hasAddress() ){
            println( order.getCustomer().getAddress() )


Now let's transform this code:

println( order?.getCustomer()?.getAddress() )


BoxLang offers an assert operators that will evaluate an expression and if the expression is falsey it will throw an assert exceptions.

// Asserts that the name is truthy
assert name

// Assert an expression
assert myService.hasData()
assert name.length() > 3

// Assert a lambda/closure result.
assert ()-> { do something }
assert ()=> { do something }


BoxLang functions are first-class citizens. That means you can pass them around, execute them, dynamically define them, inject them, remove them, and so much more.

It has 3 major functional types:

  • UDF—User-Defined Function—Can be created on any scripting template or within Classes. They carry no context with them.

  • Closures are named or anonymous functions that carry with them their surrounding scope and context. It uses the fat arrow => syntax.

  • Lambdas are pure functions that can be named or anonymous and carry NO enclosing scope. They are meant to be pure functions and produce no side effect. Data in, Data out. It uses the skinny arrow -> Syntax.

// A scripting UDF
function sayHello(){
    return "Hola!"
// Some class UDFs

    function init(){
        return this

    function sayHello(){
        return "Hola!"


myClass = new MyClass()

// Let's create an alias to the function
myClass.hola = myClass.sayHello
// Let's remove the sayHello function
myClass.sayHello = null

println( myClass.hola() )
// Named closure
myClosure = item => item++;
myClosure( 1 )

// Anonymous Closure
[1,2,3].filter( item => item > 2 )

// Named Lambda
myLambda = item -> item++;
myLambda( 1 )

// Anonymous Lambda
[1,2,3].filter( item -> item > 2 )

Public by default

All functions and classes are public by default, so there is no need to add the public identifier if you don't want to. This creates a very nice and low-verbosity approach to function declaration:

function hello(){}
// Same as:
public function hello(){}

// private
private function getData(){}

// protected
protected function bindData(){}

Non-required arguments by default

All arguments are NOT required by default and will be defaulted to null if not passed. You can use the required identifier to mark them as required.

function save( required user, boolean transactional = false, Logger logger ){


Default Arguments

You can create defaults for arguments, which can be literal or actual expressions:

function save( transactional = true, data = {}, scope = "#expression#" ){

function hello( name = variables.defaultName ){
    println( "Hola #arguments.name#" )

Argument Collections

Similar to var arguments in Java, BoxLang allows the arguments scope to be completely be variable. meaning you can declare the arguments, but you can pass as many as you like and they will all be added into the arguments scope.

Another feature is that you can bind and apply these arguments at function execution time from any map or structure via the argumentCollection special argument. This allows you to collect arguments and dispatch the function call, and BoxLang will match the argument names for you. This can be great for dynamic argument collection, form collection, JSON packets, etc.

function save( name, age, isActive, logIt=false ){
    .. Do your thing here!!

// Call the save using a map/struct
myMap = { name: "test", age: 40, isActive: true }
// Use the special argumentCollection designator
save( argumentCollection : myMap )

This is a great time saver.

Auto-casting Arguments & Return Values

In BoxLang, we actively cast the incoming argument value to the specified declared argument.

function setAge( numeric age )

BoxLang will try to auto cast the incoming argument to the numeric type in this instance.

It will also auto cast the outgoing return value for you. So if your function specifies that the return value is a boolean, but you return a string, it will auto cast it to boolean for you.

function Boolean isAlive(){
    return "yes"

BIFs = Built-In Functions

BoxLang is inspired by many languages, and it offers built-in functions you can call from anywhere in your code. They are automatically registered by the core language and any collaborating module.

println( "Hola from #now()#" )

To get a sense of all the BIFs registered in your runtime, do a

writedump( getFunctionList() ) or println( getFunctionList() )

Member Functions

Member functions are special functions attached to all data types in BoxLang, whether they are structs, arrays, strings, numbers, dates, Java objects, classes, etc. We provide tons of member functions, but developers can also contribute their own via BoxLang modules. All member functions map back to built-in functions.

myArray = [1,2,3,4]
println( myArray.count() )

fruitArray = [
    {'fruit'='apple', 'rating'=4},
    {'fruit'='banana', 'rating'=1},
    {'fruit'='orange', 'rating'=5},
    {'fruit'='mango', 'rating'=2},
    {'fruit'='kiwi', 'rating'=3}
favoriteFruites = fruitArray.filter( item -> item.rating >= 3 )

You can find all the collection of member functions in our types section.

BoxLang Classes

BoxLang classes are enhanced in many capabilities compared to Java, but they are similar to Groovy and CFML.

  • Automatic package definition

  • Automatic Hash Code and Equals

  • Automatic constructor created for you

  • No need to add a name to the class definition, we use the filename

  • Implements by default IClassRunnable, IReferenceable, IType, Serializable

  • Automatic getters and setters for any property definition

  • Allows for pseudo constructor blocks for initializations and more (Space between last property and first function)

  • Output is false by default for pseudo-constructors and functions

  • You can activate Implicit property accessors and mutators

  • Automatic metadata registration into the $bx BoxMeta programming object

  • Allows for single inheritance

  • Allows for interfaces

  • Allows for static blocks, functions, and properties

  • Allows for final properties (coming soon)

  • Allows for lazy properties (coming soon)

  • Allows for property observers (coming soon)

  • Allows for scope observers (coming soon)

  • Functions in a class can have different visibilities: private, public, protected, remote

Check out our Classes section for further information

Properties, not Fields

BoxLang classes can define properties as data members; they are not called fields and are always private meaning they will be stored in the variables scope. You can define them in short or long format. Please note that properties do require a semi-colon, as they can be very ambiguous.

All properties are stored in the variables scope.

Short Form

The short form allows for property [type=any] name [default=expression];


    // No type means `any`, no default means null
    property firstName;
    // A numeric age with a default value of 1
    property numeric age default=1;
    // A struct data with a default struct literal
    property struct data default={ name:"this", age : 3, whatever : now() };


Long Form

The long form allows for name-value pairs. We distinguish some value pairs from those we don't, and those we don't will be added as metadata to the property.


    property name="firstName" type="string" default="boxlang";
    property name="age" type="numeric";

    property name="data"
        default={ name:"this", age : 3, whatever : now() };


Check out our properties section for all valid attributes. Here are a few common ones

  • default - The property's default value

  • name - The property's name

  • getter - Boolean indicator to generate or not the getter for the property. Default is true

  • required - If the property requires a value or not.

  • setter - Boolean indicator to generate or not the setter for the property. Default is true

  • type - The default type of the property defaults to any

BoxLang also advertises Class creations, so modules can collaborate with extra metadata and properties or inspect the properties and act on them.

Our dependency injection framework does this.

Automatic Constructor

Constructors in classes for BoxLang are not overloads but a single init() method. However, by default we create one for you. It can also take in named parameters or an argumentCollection to initialize all properties.


	property name;
	property email;
	property isActive;


// Create a new user with no data
user = new User()

// Create one with named params
user = new User( name: "BoxLang", email: "info@boxlang.io", isActive: true )

// Create one with an arg collection
myArgs = { name: "BoxLang", email: "info@boxlang.io", isActive: true }
user = new User( argumentCollection: myArgs )

If you create your own init() then it's your job to initialize your class :)


BoxLang annotations can be added to properties, functions, and classes. Using the following pattern:

@annonationName [AnyLiteralExpression=null]

You can add as many as you like to the target locations without creating annotation classes or boilerplate. The annotation's value is completely optional and can be a literal express, which can be a string, list, array, struct, JSON, etc.

Metadata: $bx

All of these annotations and metadata can be retrieved at runtime by using the getMetadata() or getClassMetadata() bifs. You can also look at the .$bx property in every boxlang object. Which contains not only the metadata about each object, but ways to do meta-programming with it. Like adding/modifying/removing properties/functions/annotations.

Extra metadata can be added to functions, properties, classes, or annotations.

@transientCache false
@myMetadata "hello"


myClass = new MyClass()
writeOutput( myClass.$bx.meta ) or println( myClass.$bx.meta )

The $bx object is the BoxLang meta object. It contains all the necessary metadata information about an object. From it's Java Class, to functions, properties, data, etc. It can be used on ANY BoxLang Type. Here are the properties in the $bx object available to you. It also contains many methods that exist in the BoxMeta object.

  • meta - A struct of metadata about the class

  • $class - The Java Class that represents your class

Getter and Setters

By default, automatic getters and setters for properties are enabled. You can disable them all for the class or one by one. All the setters return an instance of this. You can also override them as you see fit.


    property name="firstName" type="string" default="boxlang";
    property name="age" type="numeric"

    // Override the getter
    function getAge(){
        // log it
        return variables.age

    // Override the setter
    function setFirstName( firstName ){
        // Log here
        variables.firstname = arguments.firstName;
        return this;


myClass = new MyClass().setFirstname( "luis" );

Implicit Accessors

If you don't want to see the setter/getter method calls, turn on implicit access since it's false by default.

@invokeImplicitAccessor true
    property name="firstName" type="string" default="boxlang";
    property name="age" type="numeric"

myClass = new MyClass();
myClass.age = 23
printLn( myClass.age )

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