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Platform for safe, easy and productive programming of complex, multi-platform apps with a modern user interface
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.gitattributes Restructure QtByteRunner & src folder to platforms folder (#194) Apr 27, 2019
.gitignore Ignore flowc_short_server.log Mar 18, 2020
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flow.sublime-project Initial commit to open source flow repository Dec 30, 2018
flow9.code-workspace Implement quoting expansion for some constructs now Feb 21, 2019


flow is a platform for safe, easy and productive programming of complex, multi-platform apps with a modern user interface.

The flow platform includes

  • The flow programming language, a safe, functional strongly-typed programming language
  • The flowc compiler, an incremental compiler for multiple targets
  • The flow runtime & standard library, which provides a complete cross-platform library including mature UI components

flow has production quality targets for:

  • HTML through JS
  • iOS
  • Android
  • Windows, Mac, Linux

Hello world

import runtime;

main() {
	println("Hello world");

Meet flow

  • flow is a simple, functional language in the ML family
  • C-family syntax
  • Strongly typed, polymorphism, subtypes
  • Designed to look like other languages and be easy to learn
  • Minimalistic to reduce complexity and ease porting to new platforms
  • Same code compiles and runs on HTML5, iOS, Android, Windows, macOS, Linux
  • Production quality. Software used by millions of users
  • Pixel precision—high-design, responsive UI on all platforms with identical code
  • Complete standard library written in flow itself, with natives for each backend
  • Extensive UI toolkit based on Google Material Design guidelines
  • UI toolkit based on Functional Reactive Programming


  1. Make sure you have Git LFS installed.

  2. Check out this repository with something like

    git clone

  3. Add flow9\bin to your path. We also require 64-bit Java Runtime and Python in your path.

  4. Cd into the flow9 directory and compile and run the first program:

    c:/flow9> flowcpp demos/demos.flow

If this does not work, make sure you have Git LFS installed. You have to reclone the flow9 repository after installing Git LFS, or use git lfs pull.

See demos/demos.flow to read the code for this example.


See doc/readme.markdown for further documentation about the language and platform, including more details on how to get started.


There is a blog about flow here:

There is a chat in Telegram for discussions about flow:

There is a mailing list group in about flow as well:

Your first message requires moderation approval to avoid spam.


  • flowc is the current compiler, written in flow itself. See tools/flowc. Can work as a compile server.
  • flow is the original compiler, written in haxe. See tools/flow
  • Single-step debugger using gdb protocol (see platforms/qt)
  • Profiler for time, instructions, memory, garbage collection
  • JIT (just-in-time) compiler for x64, interpreter for ARM and others
  • Compiles to C++ and Java for performance-critical code, typically server side
  • IDE/Code editor support for VSCode, Sublime Text, Kate & others
  • Mature PEG parser generator. See doc/lingo.markdown


  • bin - binaries for the compiler and related tools
  • debug - code for the debugger and profiler
  • demos - a demo program showing how the UI library can be used
  • doc - documentation of the language and libraries
  • lib - the flow standard library
  • platforms - the flow runtime platforms source code
  • resources - integrations with VS code (recommended), Sublimetext and more
  • sandbox - contains hello world
  • tools - the compiler and processor for rendering fonts
  • www - required files to be exposed by the web-server for running flow programs online
  • www_source - the source files of some of the files in the www folder


The flow compiler is licensed under GNU General Public License version 2 or any later version. The flow standard library is released under the MIT license. For the license of other components, see LICENSE.txt.


flow was started in 2010. This predates the 'flow' typechecker from Facebook. Thus, we elect to keep the name, since it came first, is a full platform and the risk of confusion seems small. However, should the need arise, then flow9 can also be used to refer to this language.


  • August 2010: The very first program ran on Flash & HTML5
  • November 2013: First app approved in iOS store
  • April 2014: First app approved in Android PlayStore
  • November 2015: Flash was retired, completely migrated to HTML5
  • January 2016: Material guidelines implemented
  • November 2016: JIT for x64 was added
  • May 2018: Self-hosted compiler written in flow itself
  • April 2019: Initial open source release
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