Mu's code looks quite alien, requiring editors to be specially configured to colorize it in a sane manner. So this page provides links to the source files showing how it currently looks in my custom setup.

Whetting your appetite: some example programs.

• x.mu: a simple program to add two numbers together. Shows that at bottom Mu is a simple VM bytecode designed to convert directly to machine code.
• factorial.mu: everyone's favorite example, showing how Mu supports conditionals and loops without any special syntax, using the special labels '{' and '}'.
• tangle.mu: another (contrived) version of factorial showing Mu's ability to 'tangle' code from multiple places into a single function or 'recipe'.
• counters.mu: lexical scope
• simple examples showing off support for concurrency: fork.mu, channel.mu
• simple examples showing off hardware control: display.mu, console.mu.
• screen.mu: example program showing print primitives that inject a screen dependency which can be faked for testing.
• static_dispatch.mu: example program showing mu's ability to define functions with headers, and allow functions with the same name but different headers to coexist.
• chessboard.mu: a little program for 2 people to play chess, with thorough tests of its behavior including both screen and keyboard handling.

Part I: basic infrastructure

000organization.cc: the basic skeleton program. Compiles and runs but doesn't do much. Later layers hook into this skeleton to add functionality. Mu's guarantee: you can load features up until any layer, and it will compile and pass all tests until that point. More details →
001help.cc: just a simple test layer to show how to hook into the skeleton. Also summarizes how to invoke Mu, behaviors that later layers will be providing.
002test.cc: Mu's minimalist test harness, relying on a couple of one-liners in the makefile to autogenerate lists of tests to run.
003trace.cc: support for logging facts about our program, and for checking the facts logged in tests. (tests for the test harness)

Part II: the Mu virtual machine, designed to compile easily to machine language.

010vm.cc: core data structures: functions, instructions and reagents (operands).
011load.cc: the textual representation of functions and how it's turned into the data structures.
012transform.cc: after Mu programs are loaded but before they are run they can be transformed in an extensible manner akin to lisp macros. Think of this as the core of Mu's ‘compiler’ for providing high-level features atop the core.
013update_operation.cc: our first transform: check for unknown functions before the program runs.
014literal_string.cc: extend the loader to support literal strings in various instructions.
015literal_noninteger.cc: extend the loader to support non-integer numbers.
020run.cc: executing Mu functions by executing the list of instructions they contain. Future layers will define more primitive operations that can be used in instructions.
021check_instruction.cc: harness for adding per-primitive checks to run before running a program.
Various primitive operations: on numbers, booleans, for control flow, and comparing values.
026call.cc: calls to functions look just like primitive operations.
027call_ingredient.cc: how functions pass arguments or 'ingredients' without introducing any syntax and breaking the metaphor of functions as lists of instructions.
028call_reply.cc: functions can return arbitrary numbers of values to their callers.
029tools.cc: various primitive operations to help with testing and debugging.

030container.cc: Mu supports compound types called containers akin to records, structs or classes.
031array.cc: all Mu data structures are bounds-checked.
032exclusive_container.cc: tagged unions or sum types.
033address.cc: Mu requires you to manually manage memory. However, it provides transparent refcounting for all addresses, making it entirely safe from the sorts of undefined behavior and security vulnerabilities that plague C. Compared to Rust, Mu gives up some runtime efficiency in exchange for C-like flexibility (you can copy addresses around all you like, and write from any copy of an address) and simpler implementation (since I punt on Rust's static analysis).

061recipe.cc: passing functions around as first-class values in higher-order functions.
062scheduler.cc: running multiple functions concurrently using routines that might execute in interleaved fashion.
063wait.cc: primitives for synchronization between routines.

Part III: transforms to provide 80% of the benefits of high-level languages.
040brace.cc and 041jump_target.cc: how Mu provides structured goto-less programming without introducing the syntax of conditionals and loops other languages require.
042name.cc: how Mu transforms variable names to raw memory addresses.
043space.cc: how variables in different routines are isolated from each other using spaces. Mu ‘local variables’ are allocated on the heap.
044space_surround.cc: Chaining spaces together to accomodate variables with varying lifetimes and ownership properties.
045closure_name.cc: how spaces can implement lexical scope.
046global.cc: experimental support for 'global' variables that are always available inside a single routine. Mu has no variables that are available transparently across routines, and this might go away as well. Global variables are currently not checked as rigorously as the rest of the type system.
047check_type_by_name.cc: a simple transform to deduce missing types in instructions on the basis of previous instructions in the same function.
050scenario.cc: Mu's first syntax — not for code but for tests. (example)
052tangle.cc: support for layers in Mu programs. They've been so good to us.
Support for shape-shifting or generic data structures that can contain type ingredients: 053dilated_reagent.cc, a new syntax for allowing whitespace in types; 054parse_tree.cc, a new syntax for representing complex types as trees using whitespace and parentheses (s-expressions); 055recipe_header.cc, a new syntax for introducing ingredients and products with the name of a reagent; 056static_dispatch.cc, allowing multiple variants of a function to coexist with support for different headers; 057shape_shifting_container.cc, a new syntax for wildcard type ingredients in containers; and finally 058shape_shifting_recipe.cc, support for type ingredients in functions. Everytime you call a shape-shifting function with a new set of types for its type ingredients, it creates a new variant of the function for you matching those types.
060immutable.cc, a static analysis to ensure that functions never modify anything but their products.

998check_type_pointers.cc.html: After all our messing about with types, a final pass to make sure we didn't introduce any invalid types.
999spaces.cc.html: Maps summarizing various address spaces in the core, and the conventions that regulate their use in previous layers. various address spaces in the core, and the conventions that regulate their use in previous layers.

Part IV: beginnings of a standard library

070text.mu: strings in Mu are bounds-checked rather than null-terminated. They're also unicode-aware (code points only; no control characters, no combining characters, no normalization).
064rewrite_literal_string.cc: allow functions taking strings to also take string literals. Mu doesn't have a global segment; string literals are allocated on the heap everytime they're used.
071rewrite_stash.cc: a convenience when debugging is the ability to add variables to the trace using the stash command. By default stash just prints out the locations in memory, one by one. To extend its display format specific types, define a function called to-text with the appropriate ingredient type, returning a Mu string.
072channel.mu: channels are Mu's only synchronization primitive, queues that can cause the routine reading or writing from them to stall without taking up CPU resources.
073array.mu
074list.mu: linked lists where each node points to the next, permitting fast insertion/deletion but slow for search.
075random.cc
076duplex_list.mu: doubly linked lists that can be traversed both forwards and back.
077stream.mu: data structure to efficiently append strings.

Part V: Nascent tools for browsing Mu codebases, and for teaching programming to non-programmers by getting them hooked on the value of tests. The eventual goal is an environment that watches programmers as they manually test their code, and turns these interactive sessions into reproducible test scenarios.

080display.cc: primitives for using the keyboard and screen.
081print.mu: helpers that can swap the real screen with fake ones for testing.
082scenario_screen.cc: writing tests that check what is printed to screen. (examples)
084console.mu: helpers that can swap the real keyboard and mouse with fake ones for testing.
085scenario_console.cc: writing tests for keyboard and mouse using the fakes. (examples)
090trace_browser.cc: a zoomable UI for inspecting traces generated by Mu programs. Allows both scanning a high-level view and drilling down into selective details.
091run_interactive.cc: hacky primitives for running Mu code in the programming environment below.
092persist.cc: more hacky primitives for supporting saving/restoring sessions in the Mu programming environment.

Finally, the programming environment, the first major application in its own directory. Stop loading after each of these layers to get a working version with just fewer features. The readme for the app contains instructions for running it.

edit/001-editor.mu: data structures for a simple text editor widget. Load just this layer to see just the rendering and line-wrapping at work.
edit/002-typing.mu: support for moving the cursor anywhere with the mouse and typing text in there.
edit/003-shortcuts.mu: support for various keyboard shortcuts for manipulating text you've typed in.
edit/004-programming-environment.mu: combining two text editor widgets, one on the left, one on the right.
edit/005-sandbox.mu: support for running mu code in the right-hand widget using code from the left, and displaying results in a sandbox below on the right. You can have multiple sandboxes, and hit F4 to rerun them all at anytime with the latest version of the code on the left side.
edit/006-sandbox-edit.mu: click on the title bar of each sandbox to pop it back into the sandbox editor and make changes to it.
edit/007-sandbox-delete.mu: click on the 'x' in the title bar of a sandbox to delete it.
edit/008-sandbox-test.mu: click on the results of a sandbox to turn them green and save the output as golden/expected. Any future changes to the output will then be flagged in red.
edit/009-sandbox-trace.mu: click on code in a sandbox to open up a drawer containing its trace. The trace can be added to using the stash command, which renders arbitrary data structures using to-text with the appropriate function header.
edit/010-errors.mu: support for rendering errors on both the left and in each sandbox.
edit/011-editor-undo.mu: support for undo in the editor widget.

The zen of mu:

• traces, not interfaces
• be rewrite-friendly, not backwards-compatible
• be easy to port rather than portable
• global structure matters more than local hygiene

Mu's vision of utopia:

• Run your devices in 1/1000th the code.
• 1000x more forks for open source projects.
• Make simple changes to any project in an afternoon, no matter how large it is.
• Projects don't slow down with age, they continue to evolve just as fast as when they were first started.
• All software rewards curiosity, allowing anyone to query its design decisions, gradually learn how to tweak it, try out increasingly radical redesign ideas in a sandbox. People learn programming as an imperceptible side effect of tinkering with the projects they care about.
• Habitable digital environments.
• A literate digital society with widespread skills for comprehending large-scale software structure and comparing-and-contrasting similar solutions. (I don't think anybody is literate by this definition today. All we can do easily is read our own programs that we wrote recently.)