We've built up similarly *dependency-injected* interfaces to the keyboard,
mouse, disk and network.
1. Support for testing side-effects like performance, deadlock-freedom,
race-freeness, memory usage, etc. Mu's *white-box tests* can check not just
the results of a function call, but also the presence or absence of
specific events in the log of its progress. For example, here's a test that
our string-comparison function doesn't scan individual characters unless it
has to:
Another example: if a sort function logs each swap, a performance test can
ensure that the number of swaps doesn't quadruple when the size of the
input doubles.
Besides expanding the scope of tests, this ability also allows more
radical refactoring without needing to modify tests. All Mu's tests call a
top-level function rather than individual sub-systems directly. As a result
the way the subsystems are invoked can be radically changed (interface
changes, making synchronous functions asynchronous, etc.). As long as the
new versions emit the same implementation-independent events in the logs,
the tests will continue to pass. ([More information.](http://akkartik.name/post/tracing-tests))
1. Organizing code and tests in layers of functionality, so that outsiders can
build simple and successively more complex versions of a project, gradually
enabling more peripheral features. Think of it as a cleaned-up `git log`
for the project. ([More information.](http://akkartik.name/post/wart-layers))
These mechanisms exist in the context of a low-level statement-oriented
language (like Basic, or Assembly). The language is as powerful as C for
low-level pointer operations and manual memory management, but much safer,
paying some run-time overhead to validate pointers. It also provides a number
of features usually associated with higher-level languages: strong
type-safety, function overloading, lexical scope, generic functions,
higher-order functions, and [delimited continuations](http://akkartik.name/coroutines-in-mu).
Mu is currently interpreted and too slow for graphics or sound. We're
actively investigating ways to speed it up. In the meantime, Kartik uses it to
teach programming 1-on-1 with the motto, "teach testing before syntax."
*Taking Mu for a spin*
Mu is currently implemented in C++ and requires a Unix-like environment. It's
been tested on Ubuntu, Mac OS X and OpenBSD; on x86, x86\_64 and ARMv7; and on
recent versions of GCC and Clang. Since it uses no bleeding-edge language
features and has no exotic dependencies, it should work with most reasonable
versions, compilers or processors.
[](http#!/bin/bash
# Regenerate html files.
set -e
( cd linkify; build; )
# generate html/$1.html using /tmp/tags
process() {
rm -f html/$1.html
convert_html $1
linkify/linkify /tmp/tags html/$1.html
mv html/$1.html.out html/$1.html
}
convert_html() {
vim -c "set number" -c TOhtml -c write -c qall $1
sed -i 's,<title>.*/mu/,<title>Mu - ,' $1.html
sed -i 's,\.html</title>,</title>,' $1.html
sed -i 's/^\* { \(.*\) }/* { font-size: 12pt; \1 }/g' $1.html
sed -i 's/^body { \(.*\) }/body { font-size: 12pt; \1 }/g' $1.html
# turn most code grey
sed -i 's/#eeeeee/#aaaaaa/g' $1.html
# ..so that we can use white for cross-links (underlining only on hover)
sed -i '/^body {/ a a:hover { text-decoration: underline; }' $1.html
sed -i '/^body {/ a a { color:#eeeeee; text-decoration: none; }' $1.html
# line numbers are darker still
sed -i 's/^\.LineNr .*/.LineNr { color: #444444; }/' $1.html # line numbers
# tweak contrast for remaining colors
sed -i 's/^\.Constant .*/.Constant { color: #00a0a0; }/' $1.html
sed -i 's/^\.muControl .*/.muControl { color: #c0a020; }/' $1.html
# real links in comments continue to be the usual blue
sed -i 's/^\.Comment .*/.Comment { color: #9090ff; }\n.Comment a { color:#0000ee; text-decoration:underline; }/' $1.html
sed -i 's/^\.Delimiter .*/.Delimiter { color: #800080; }/' $1.html # not meant to be read; can be lower-contrast
sed -i 's/^\.PreProc .*/.PreProc { color: #800080; }/' $1.html # not meant to be read; can be lower-contrast
sed -i 's/^\.Identifier .*/.Identifier { color: #c0a020; }/' $1.html # same as muControl
sed -i 's/^\.Special .*/.Special { color: #c00000; }/' $1.html # same as traceAbsent..
# switch unicode characters around in the rendered html
# the ones we have in the source files render double-wide in html
# the ones we want in the html cause iTerm2 to slow down in alt-tabbing for some reason
# the following commands give us the best of both worlds
sed -i -e 's/┈/╌/g' -e 's/┊/╎/g' $1.html
mv -i $1.html html/`dirname $1`
}
ctags -x *.cc |grep -v "^operator \| member \| variable " > /tmp/tags
for f in *.cc