FLang

FLang is a simple interpreted programming language with the .flg file extension. Its interpreter is written in Python and distributed through npm so it can be run from the terminal.

The npm package also includes a VS Code extension that provides syntax highlighting, editor configuration, and a custom icon for .flg files.

Features

• Variables with var and reassignment.
• Strings and numbers.
• The +, -, ==, >, and < operators.
• if and else conditionals.
• while loops.
• Functions with parameters.
• Built-in print and input functions.
• Single-line comments with //.
• Syntax highlighting and .flg icons for VS Code, VS Code Insiders, and VSCodium.

Installation

Prerequisites

• Node.js 16 or later.
• Python 3.
• VS Code, VS Code Insiders, or VSCodium (optional, for syntax highlighting and file icons).

Install FLang globally:

npm install -g @fareldev-hub/flang

During installation, FLang automatically checks for Python 3 and pip. When both are available, it runs:

python3 -m pip install lark

On Windows, FLang also tries the Python Launcher (py -3).

If Python is not installed, download it from:

https://www.python.org/downloads/

If Python is installed but pip is unavailable, follow the official pip installation guide:

https://pip.pypa.io/en/stable/installation/

After installing Python or pip, run the npm installation again:

npm install -g @fareldev-hub/flang

The npm installation also tries to install the bundled FLang extension into any VS Code-compatible editor available in PATH. If no compatible editor is found, the interpreter is still installed and npm does not fail.

To skip automatic VS Code extension installation:

FLANG_SKIP_VSCODE_INSTALL=1 npm install -g @fareldev-hub/flang

If the extension was not installed automatically, install it manually:

code --install-extension "$(npm root -g)/@fareldev-hub/flang/vscode-extension"

Once the extension is active, .flg files are recognized as FLang files, receive syntax highlighting, and use the FLang file icon.

Quick start

Create a file named hello.flg:

var name = "Andi"
print "Hello " + name

var age = 20
if age > 18 {
    print "Adult"
} else {
    print "Underage"
}

func greet(person) {
    print "Welcome, " + person
}

greet(name)

var i = 0
while i < 3 {
    print i
    i = i + 1
}

Run it with either command:

flang hello.flg

or:

flang run hello.flg

Output:

Hello Andi
Adult
Welcome, Andi
0
1
2

Show the version

flang -v

or:

flang --version

The displayed version is read directly from the npm package's package.json.

Show FLang information

Running flang without a file displays the language name, version, creator, an description, and usage examples:

flang

Syntax reference

Variables

Use var when declaring a new variable. Reassignment does not require var.

var name = "Budi"
var age = 18
age = 19

Strings and numbers

Strings use double quotation marks. The current implementation supports integer numbers.

var message = "Hello"
var count = 10
print message
print count

Print

print accepts one or more comma-separated expressions.

print "Hello world"
print "Name:", name, "Age:", age

The + operator can concatenate strings with other values.

print "Count: " + 10

Operators

| Operator | Purpose | Example | | --- | --- | --- | | + | Add or concatenate values | a + b | | - | Subtract numbers | a - b | | == | Compare equality | a == b | | > | Check whether a value is greater | a > b | | < | Check whether a value is smaller | a < b |

If and else

Code blocks are written between { and }.

if age == 18 {
    print "Exactly 18"
} else {
    print "Not 18"
}

While

var i = 0
while i < 5 {
    print i
    i = i + 1
}

Functions

Define functions with func. The current version does not support return.

func greet(name) {
    print "Hello " + name
}

greet("Budi")

Functions can have multiple parameters:

func show(name, age) {
    print name, age
}

show("Budi", 20)

Input

Use input to read text from the terminal.

var name = input("What is your name? ")
print "Hello " + name

Comments

Single-line comments start with //.

// This is a comment
var value = 10 // A comment after code

Running from source

If you do not want to install the npm package globally:

python3 -m pip install lark
node bin/flang.js hello.flg

VS Code extension

The extension is located in the vscode-extension directory. It provides:

• The flang language definition for .flg files.
• Syntax highlighting for keywords, functions, numbers, strings, operators, and comments.
• A custom .flg file icon.
• Automatic closing for {}, (), and quotation marks.

Install the extension from source:

code --install-extension ./vscode-extension

Current limitations

• Functions do not support return yet.
• else if is not supported yet.
• The *, /, and % operators are not supported yet.
• Error messages do not always include line numbers.
• The currently available built-ins are input and print.

License

FLang is released under the MIT License. See LICENSE for the full license text.