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<title>Mu</title>

With apologies to <a href='http://en.wikipedia.org/wiki/Mu_%28negative%29#In_popular_culture'>Robert Pirsig</a>:
<p>
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Is it a language, or an operating system, or a virtual machine?
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Mu.
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Read these first: <a href='http://akkartik.name/about'>problem statement</a>,
<a href='http://github.com/akkartik/mu#readme'>readme and installation
  instructions</a> (mu requires minimal dependencies).

<p>
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 <a href='https://github.com/akkartik/mu/blob/master/mu.vim'>custom setup</a>.

<p>Whetting your appetite: some example programs.

<ul>
<li><a href='html/x.mu.html'>x.mu</a>: 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.
<li><a href='html/factorial.mu.html'>factorial.mu</a>: everyone's favorite
example, showing how mu supports conditionals and loops without any special
syntax, using the special labels '{' and '}'.
<li><a href='html/tangle.mu.html'>tangle.mu</a>: another (contrived) version
of factorial showing mu's ability to 'tangle' code from multiple places into a
single function or 'recipe'.
<li><a href='html/counters.mu.html'>counters.mu</a>: lexical scope
<li><a href='html/callcc.mu.html'>callcc.mu</a>: first-class continuations. Mu
also supports first-class functions and delimited continuations.
<li>simple examples showing off support for concurrency: <a href='html/fork.mu.html'>fork.mu</a>,
<a href='html/channel.mu.html'>channel.mu</a>
<li>simple examples showing off hardware control: <a href='html/display.mu.html'>display.mu</a>,
<a href='html/console.mu.html'>console.mu</a>.
<li><a href='html/screen.mu.html'>screen.mu</a>: example program showing
print primitives that inject a screen <em>dependency</em> which can be faked
for testing.
<li><a href='html/chessboard.mu.html'>chessboard.mu</a>: putting it all
together, a little console program along with thorough tests of its behavior
including both screen and keyboard handling.
<li><a href='html/edit.mu.html'>edit.mu</a>: the programming environment I
plan to use to teach programming.
</ul>

<p><b>Part I</b>: basic infrastructure
<p/><a href='html/000organization.cc.html'>000organization.cc</a>: the basic
skeleton program. Compiles and runs but doesn't do much. Later <em>layers</em>
hook into this skeleton to add functionality. Mu's guarantee: you can <a href='http://youtube.com/watch?v=c8N72t7aScY'>load
features</a> up until any layer, and it will compile and pass all tests until
that point. <a href='http://akkartik.name/post/wart-layers'>More details &rarr;</a>
<br/><a href='html/001help.cc.html'>001help.cc</a>: 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.
<br/><a href='html/002test.cc.html'>002test.cc</a>: mu's minimalist test
harness, relying on a couple of one-liners in the makefile to autogenerate
lists of tests to run.
<br/><a href='html/003trace.cc.html'>003trace.cc</a>: support for logging
facts about our program, and for <a href='http://akkartik.name/post/tracing-tests'>checking the facts logged in tests</a>.
(<a href='html/003trace.test.cc.html'>tests for the test harness</a>)

<p><b>Part II</b>: the mu virtual machine, designed to compile easily to
machine language.
<p/><a href='html/010vm.cc.html'>010vm.cc</a>: core data structures: recipes
(functions), instructions and reagents (operands).
<br/><a href='html/011load.cc.html'>011load.cc</a>: the textual representation
of recipes and how it's turned into the data structures.
<br/><a href='html/012transform.cc.html'>012transform.cc</a>: 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
&lsquo;compiler&rsquo; for providing high-level features atop the core.
<br/><a href='html/013literal_string.cc.html'>013literal_string.cc</a>: extend
the loader to support literal strings in various instructions.
<br/><a href='html/014literal_noninteger.cc.html'>014literal_noninteger.cc</a>:
extend the loader to support non-integer numbers.
<br/><a href='html/020run.cc.html'>020run.cc</a>: executing mu recipes by
executing the list of instructions they contain.
<br/>Various primitive operations: on <a href='html/021arithmetic.cc.html'>numbers</a>,
<a href='html/022boolean.cc.html'>booleans</a>, for <a href='html/023jump.cc.html'>control flow</a>,
and <a href='html/024compare.cc.html'>comparing values</a>.
<br/>Primitive operations to help with testing: <a href='html/025trace.cc.html'>tracing/logging</a>, 
<a href='html/026assert.cc.html'>assert</a> and
<a href='html/027debug.cc.html'>debug by print</a>.

<br/><a href='html/030container.cc.html'>030container.cc</a>: compound types
akin to records, structs or classes.
<br/><a href='html/031address.cc.html'>031address.cc</a>: adding and removing
layers of indirection to mu data.
<br/><a href='html/032array.cc.html'>032array.cc</a>: all mu data structures
are bounds-checked.
<br/><a href='html/033exclusive_container.cc.html'>033exclusive_container.cc</a>: tagged unions or sum types.
<br/><a href='html/034call.cc.html'>034call.cc</a>: calls to recipes look
just like primitive operations.
<br/><a href='html/035call_ingredient.cc.html'>035call_ingredient.cc</a>: how
recipes pass arguments or 'ingredients' without introducing any syntax and
breaking the metaphor of recipes as lists of instructions.
<br/><a href='html/036call_reply.cc.html'>036call_reply.cc</a>: recipes can
return arbitrary numbers of values to their callers.
<br/><a href='html/037recipe.cc.html'>037recipe.cc</a>: passing recipes around
as first-class values in higher-order functions.
<br/><a href='html/038scheduler.cc.html'>038scheduler.cc</a>: running multiple
recipes concurrently using <em>routines</em> that might execute in interleaved
fashion.
<br/><a href='html/039wait.cc.html'>039wait.cc</a>: primitives for
synchronization between routines.

<p><b>Part III</b>: transforms to provide 80% of the benefits of high-level
languages.
<br/><a href='html/040brace.cc.html'>040brace.cc</a> and
<a href='html/041jump_label.cc.html'>041jump_label.cc</a>: how mu provides
structured goto-less programming without introducing the syntax of
conditionals and loops other languages require.
<br/><a href='html/042name.cc.html'>042name.cc</a>: how mu transforms variable
names to raw memory addresses.
<br/><a href='html/043new.cc.html'>043new.cc</a>: rudimentary memory
allocator that is aware of all global types in any mu program.
<br/><a href='html/044space.cc.html'>044space.cc</a>: how variables in
different routines are isolated from each other using <em>spaces</em>. Mu
&lsquo;local variables&rsquo; are allocated on the heap.
<br/><a href='html/045space_surround.cc.html'>045space_surround.cc</a>:
Chaining spaces together to accomodate variables with varying lifetimes and
ownership properties.
<br/><a href='html/046closure_name.cc.html'>046closure_name.cc</a>: how spaces
can implement lexical scope.
<br/><a href='html/047global.cc.html'>047global.cc</a>: support for 'global'
variables that are always available inside a single routine. Mu has no
variables that are available transparently across routines.
<br/><a href='html/048typecheck.cc.html'>048typecheck.cc</a>: a simple
transformer to insert missing types in instructions.
<br/><a href='html/050scenario.cc.html'>050scenario.cc</a>: mu's first syntax
&mdash; not for code but for tests. (<a href='html/051scenario_test.mu.html'>example</a>)
<br/><a href='html/052tangle.cc.html'>052tangle.cc</a>: support for layers in
mu programs. They've been so good to us.
<br/><a href='html/053continuation.cc.html'>053continuation.cc</a>:
first-class and delimited continuations, primitives for yield, exceptions and
much else besides.

<p><b>Part IV</b>: beginnings of a standard library
<p/><a href='html/060string.mu.html'>060string.mu</a>: strings in mu are
bounds-checked rather than null-terminated. They're also unicode-aware.
<br/><a href='html/061channel.mu.html'>061channel.mu</a>: 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.
<br/><a href='html/062array.mu.html'>062array.mu</a>
<br/><a href='html/063list.mu.html'>063list.mu</a>: linked lists where each
node points to the next, permitting fast insertion/deletion but slow for
search.
<br/><a href='html/064random.cc.html'>064random.cc</a>
<br/><a href='html/065duplex_list.mu'>065duplex_list.mu</a>: doubly linked
lists that can be traversed both forwards and back.
<br/><a href='html/066stream.mu'>066stream.mu</a>: data structure to
efficiently append strings.

<p><b>Part V</b>: 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 <b>an environment that watches programmers as they
manually test their code, and turns these interactive sessions into
reproducible test scenarios.</b>

<p/><a href='html/070display.cc.html'>070display.cc</a>: primitives for using
the keyboard and screen.
<br/><a href='html/071print.mu.html'>071print.mu</a>: helpers that can swap
the real screen with fake ones for testing.
<br/><a href='html/072scenario_screen.cc.html'>072scenario_screen.cc</a>:
writing tests that check what is printed to screen.
(<a href='html/073scenario_screen_test.mu.html'>examples</a>)
<br/><a href='html/074console.mu.html'>074console.mu</a>: helpers that can
swap the real keyboard and mouse with fake ones for testing.
<br/><a href='html/075scenario_console.cc.html'>075scenario_console.cc</a>:
writing tests for keyboard and mouse using the fakes.
(<a href='html/076scenario_console_test.mu.html'>examples</a>)
<br/><a href='html/080trace_browser.cc.html'>080trace_browser.cc</a>: a
zoomable UI for inspecting traces generated by mu programs. Allows both
scanning a high-level view and drilling down into selective details.
<br/><a href='html/081run_interactive.cc.html'>081run_interactive.cc</a>:
hacky primitives for supporting the mu programming environment in <a
href='html/edit.mu.html'>edit.mu</a>.
<br/><a href='html/082persist.cc.html'>082persist.cc</a>: more hacky
primitives for supporting saving/restoring sessions in the mu programming
environment.

<p/><a href='html/999spaces.cc.html'>Epilogue</a>: maps summarizing various
address spaces, and the conventions that regulate their use in previous
layers.

<hr>

<p>
The zen of mu:
<ul>
<li>traces, not interfaces
<li>be rewrite-friendly, not backwards-compatible
<li>be easy to port rather than portable
<li>global structure matters more than local hygiene
</ul>

<p>
Mu's vision of utopia:
<ul>
<li>Run your devices in 1/1000th the code.
<li>1000x more forks for open source projects.
<li>Make simple changes to any project in an afternoon, no matter how large it is.
<li>Projects don't slow down with age, they continue to evolve just as fast as
when they were first started.
<li>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.
<li><a href='https://www.dreamsongs.com/Files/PatternsOfSoftware.pdf'>Habitable</a> digital environments.
<li>A <em>literate</em> 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.)
</ul>

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