The project

Where Fubby is today, how it's changed, what's missing, and how to learn it.

Status

Fubby 0.1.2 is an experimental developer preview. Its syntax, library and behaviour can change between versions, including in ways that break existing programs. It isn't ready for production use.

Area	Today
Language	Usable for learning, scripts and local apps
Platforms	macOS on Intel only. Apple Silicon and Linux are untested, and Windows is unsupported
Testing	Automated tests pass on the Intel build machine. A test on a separate clean machine is still pending
Signing	Binaries aren't signed or notarized
Security	No independent audit, and no sandbox
License	Proprietary, and free to use. See below

What changed

Version 0.1.2

Adds the Fubby Software License and third-party notices. The language is the same as 0.1.1.

Version 0.1.1: new

A checker that finds mistakes before a program runs, and reports all of them with their position
break, continue and match
null, with optional types such as String?
The List, Map and Any types, so functions can take collections
list[0] = x and map["key"] = x, and trailing commas
Uncaught errors now name their file, line and column

Version 0.1.1: fixed

let inside a loop failed on its second pass
Classes couldn't hold other objects, and interfaces couldn't be used as types
Printing or comparing a list containing itself crashed
Deeply nested code, deeply nested data, and closed output pipes crashed
An empty for loop over a huge range ignored the time and step limits
Names using Indian scripts, such as नमस्ते, were rejected
Recursion stopped at 64 calls, and now stops at 1000

Version 0.1.1: changes that can break 0.1.0 programs

break, continue, match, case and null are now reserved words.
A variable declared in a block no longer exists after that block.
A for variable no longer exists after its loop, and can't reuse a visible name.
list_remove now returns a new list without the item.
print shows null as null.
fubby run refuses a program with a checker error, even on a line that would never run.
main must take no parameters and return nothing.
Duplicate declarations, and functions named like built-ins, are now errors.
A child class can't read a parent's private member. Declare it protected.

What's missing

These are known gaps. This list isn't a promise or a schedule.

Language

First-class functions and closures
Module namespaces
Generics and typed collections
Exact decimal numbers

Libraries

Password hashing and secure random numbers
Full regular expressions, with capture and replace
Folder listing and file deletion
CSV, Excel and PDF support
Other databases, such as PostgreSQL

Platform and tools

Windows, Apple Silicon and Linux downloads
Signed binaries
A sandbox for untrusted code
A step-through debugger
A public package registry

Web

HTTPS
Login and sessions
File uploads
WebSockets
HTTP methods beyond GET and POST in Moon

The textbook

Programming with Fubby, first edition, by Tushar H. Kshirsagar, Twig Software Solutions Pvt. Ltd. It's a 160-page student and instructor edition, with 15 chapters following the example projects, plus activities, a capstone project, a glossary and instructor notes.

Read the current manuscript (PDF)

It was written for version 0.1.0, so check what changed as you read. In particular, Chapter 9 uses list_remove, which now returns a new list.

Example projects

These 15 projects build from a greeting to a complete app. Each folder has source code, commands and the expected result. Browse all examples, or download them with Code → Download ZIP on GitHub.

Folder	What you learn
`01-hello`	Your first program, and expressions
`02-control-flow`	Types and control flow
`03-functions`	Functions and recursion
`04-classes`	Classes and encapsulation
`05-inheritance`	Inheritance and interfaces
`06-collections-imports-errors`	Collections, imports and exceptions
`07-standard-library`	Strings, math, files and time
`08-runtime`	How programs run
`09-core-library`	Collections, JSON, encoding and environment
`10-moon`	SQLite and network policy
`11-shady`	Developer tools
`12-snow`	A web application
`13-bela`	Tasks and channels
`14-smokey`	Local packages
`15-integrated-app`	A complete notes application

Common questions

Is Fubby free?

Yes. The Fubby Software License lets anyone use it for free, including for business.

Is Fubby open source?

No. Fubby is proprietary. The compiled program, documentation and examples are public, and the interpreter's source code isn't.

Who owns the programs I write?

You do. You can sell them and license them however you like, and you can ship fubby with them.

Can I use it in production?

No. It's an experimental preview, without the security features or stability that production needs.

What is it written in?

The interpreter is written in Rust, and you don't need Rust to use it.

Is it compiled or interpreted?

Interpreted. Fubby reads your source, checks it, then runs it directly. There's no separate build step.

Can AI tools write Fubby?

Fubby is new, so most AI tools don't know it yet. Giving one the language guide helps, and fubby check catches many of its mistakes. We haven't measured how well this works.

Why are types written before the name?

That's Fubby's syntax: let Int count = 1 and func add(Int a, Int b). Forms like count: Int aren't accepted.

Why is there no `switch`?

Fubby has match instead, which can't fall through to the next case by accident.

License

You may

Use Fubby for free, for any purpose, including business
Own, sell and license the programs you write
Give unmodified copies to others, and ship them with your apps

You may not

Sell Fubby itself, or modify and redistribute it
Offer it as a service for running other people's Fubby programs
Remove its notices, or reverse engineer it where the law allows that limit
Suggest that Twig made or endorses your work

Part	Terms
The `fubby` program and VS Code plugin	Fubby Software License
Example projects and starter project	MIT license
Third-party components	Their own licenses, listed in the third-party notices
This website and the textbook	All rights reserved

Fubby comes with no warranty. It's an experimental preview, so read the limits and safety notes first.