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Rip out everything to fix one failing unit test (commit 3290; type
abbreviations).
This commit does several things at once that I couldn't come up with a
clean way to unpack:
A. It moves to a new representation for type trees without changing
the actual definition of the `type_tree` struct.
B. It adds unit tests for our type metadata precomputation, so that
errors there show up early and in a simpler setting rather than dying
when we try to load Mu code.
C. It fixes a bug, guarding against infinite loops when precomputing
metadata for recursive shape-shifting containers. To do this it uses a
dumb way of comparing type_trees, comparing their string
representations instead. That is likely incredibly inefficient.
Perhaps due to C, this commit has made Mu incredibly slow. Running all
tests for the core and the edit/ app now takes 6.5 minutes rather than
3.5 minutes.
== more notes and details
I've been struggling for the past week now to back out of a bad design
decision, a premature optimization from the early days: storing atoms
directly in the 'value' slot of a cons cell rather than creating a
special 'atom' cons cell and storing it on the 'left' slot. In other
words, if a cons cell looks like this:
o
/ | \
left val right
..then the type_tree (a b c) used to look like this (before this
commit):
o
| \
a o
| \
b o
| \
c null
..rather than like this 'classic' approach to s-expressions which never
mixes val and right (which is what we now have):
o
/ \
o o
| / \
a o o
| / \
b o null
|
c
The old approach made several operations more complicated, most recently
the act of replacing a (possibly atom/leaf) sub-tree with another. That
was the final straw that got me to realize the contortions I was going
through to save a few type_tree nodes (cons cells).
Switching to the new approach was hard partly because I've been using
the old approach for so long and type_tree manipulations had pervaded
everything. Another issue I ran into was the realization that my layers
were not cleanly separated. Key parts of early layers (precomputing type
metadata) existed purely for far later ones (shape-shifting types).
Layers I got repeatedly stuck at:
1. the transform for precomputing type sizes (layer 30)
2. type-checks on merge instructions (layer 31)
3. the transform for precomputing address offsets in types (layer 36)
4. replace operations in supporting shape-shifting recipes (layer 55)
After much thrashing I finally noticed that it wasn't the entirety of
these layers that was giving me trouble, but just the type metadata
precomputation, which had bugs that weren't manifesting until 30 layers
later. Or, worse, when loading .mu files before any tests had had a
chance to run. A common failure mode was running into types at run time
that I hadn't precomputed metadata for at transform time.
Digging into these bugs got me to realize that what I had before wasn't
really very good, but a half-assed heuristic approach that did a whole
lot of extra work precomputing metadata for utterly meaningless types
like `((address number) 3)` which just happened to be part of a larger
type like `(array (address number) 3)`.
So, I redid it all. I switched the representation of types (because the
old representation made unit tests difficult to retrofit) and added unit
tests to the metadata precomputation. I also made layer 30 only do the
minimal metadata precomputation it needs for the concepts introduced
until then. In the process, I also made the precomputation more correct
than before, and added hooks in the right place so that I could augment
the logic when I introduced shape-shifting containers.
== lessons learned
There's several levels of hygiene when it comes to layers:
1. Every layer introduces precisely what it needs and in the simplest
way possible. If I was building an app until just that layer, nothing
would seem over-engineered.
2. Some layers are fore-shadowing features in future layers. Sometimes
this is ok. For example, layer 10 foreshadows containers and arrays and
so on without actually supporting them. That is a net win because it
lets me lay out the core of Mu's data structures out in one place. But
if the fore-shadowing gets too complex things get nasty. Not least
because it can be hard to write unit tests for features before you
provide the plumbing to visualize and manipulate them.
3. A layer is introducing features that are tested only in later layers.
4. A layer is introducing features with tests that are invalidated in
later layers. (This I knew from early on to be an obviously horrendous
idea.)
Summary: avoid Level 2 (foreshadowing layers) as much as possible.
Tolerate it indefinitely for small things where the code stays simple
over time, but become strict again when things start to get more
complex.
Level 3 is mostly a net lose, but sometimes it can be expedient (a real
case of the usually grossly over-applied term "technical debt"), and
it's better than the conventional baseline of no layers and no
scenarios. Just clean it up as soon as possible.
Definitely avoid layer 4 at any time.
== minor lessons
Avoid unit tests for trivial things, write scenarios in context as much as
possible. But within those margins unit tests are fine. Just introduce them
before any scenarios (commit 3297).
Reorganizing layers can be easy. Just merge layers for starters! Punt on
resplitting them in some new way until you've gotten them to work. This is the
wisdom of Refactoring: small steps.
What made it hard was not wanting to merge *everything* between layer 30
and 55. The eventual insight was realizing I just need to move those two
full-strength transforms and nothing else.
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Standardize quotes around reagents in error messages.
I'm still sure there's issues. For example, the messages when
type-checking 'copy'. I'm not putting quotes around them because in
layer 60 I end up creating dilated reagents, and then it's a bit much to
have quotes and (two kinds of) brackets. But I'm sure I'm doing that
somewhere..
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Fix CI failure.
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Now that we no longer have non-shared addresses, we can just always
track refcounts for all addresses.
Phew!
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This should eradicate the issue of 2771.
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I'm dropping all mention of 'recipe' terminology from the Readme. That
way I hope to avoid further bike-shedding discussions while I very
slowly decide on the right terminology with my students.
I could be smarter in my error messages and use 'recipe' when code uses
it and 'function' otherwise. But what about other words like ingredient?
It would all add complexity that I'm not yet sure is worthwhile. But I
do want separate experiences for veteran programmers reading about Mu on
github and for people learning programming using Mu.
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I'm going to stop wasting precious first-line characters on 'bugfix:'.
It's going to be all bugfixes for a while I think.
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I really have only one warning left: when somebody redefines a function.
I think I'm going to just turn that into an error as well and drop the
notion of warnings altogether. Anytime we find something wrong we stop
running the program. This is a place where hygiene is justified.
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Delete all the [] that has crept in since 2377 in November.
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Stack of plans for cleaning up replace_type_ingredients() and a couple
of other things, from main problem to subproblems:
include type names in the type_tree rather than in the separate properties vector
make type_tree and string_tree real cons cells, with separate leaf nodes
redo the vocabulary for dumping various objects:
do we really need to_string and debug_string?
can we have a version with *all* information?
can we have to_string not call debug_string?
This commit nibbles at the edges of the final task, switching from
member method syntax to global function like almost everything else. I'm
mostly using methods just for STL in this project.
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This is the one major refinement on the C programming model I'm planning
to introduce in mu. Instead of Rust's menagerie of pointer types and
static checking, I want to introduce just one new type, and use it to
perform ref-counting at runtime.
So far all we're doing is updating new's interface. The actual
ref-counting implementation is next.
One implication: I might sometimes need duplicate implementations for a
recipe with allocated vs vanilla addresses of the same type. So far it
seems I can get away with just always passing in allocated addresses;
the situations when you want to pass an unallocated address to a recipe
should be few and far between.
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Reorganize layers in preparation for a better way to manage heap
allocations without ever risking use-after-free errors.
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It comes up pretty early in the codebase, but hopefully won't come up
in the mu level until we get to higher-order recipes. Potentially
intimidating name, but such prime real estate with no confusing
overloadings in other projects!
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While pushing out color support in fake screens I realized I've been
complecting the special-case of a special-case to transform
literal-string arguments for 'new'. As a result I hadn't been catching
bad habits like giving its arg the wrong type. Now we have cleaner
separation of the two variants of 'new', a few more checks, and better
error messages when we mis-call it.
Aside: I've added a third goto target. Sliding into spaghetti? Keep an
eye on it.
This goto might become a common pattern: a layer hooking into a previous
one to prevent it from happening. In this case new on literal-strings
prevents the transform for new from triggering.
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..now that we support non-integers.
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Useful check:
$ grep "[^ '\"]\[[^\"]" *.cc \
|perl -pwe 's/\Wargv\[|\WTests\[|\Wframe\[|\WMemory\[|\WName\[|\WSurrounding_space\[|\WRecipe\[|\WType\[|\WRecipe_number\[|\WType_number\[|\WBefore_fragments\[|\WAfter_fragments\[//g' \
|perl -pwe 's/\Wargv\[|\WTests\[|\Wframe\[|\WMemory\[|\WName\[|\WSurrounding_space\[|\WRecipe\[|\WType\[|\WRecipe_number\[|\WType_number\[|\WBefore_fragments\[|\WAfter_fragments\[//g' \
|grep '[^ ]\['
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All primitives now always write to all their products. If a product is
not used that's fine, but if an instruction seems to expect too many
products mu will complain.
In the process, many primitives can operate on more than two ingredients
where it seems intuitive. You can add or divide more than two numbers
together, copy or negate multiple corresponding locations, etc.
There's one remaining bit of ugliness. Some instructions like
get/get-address, index/index-address, wait-for-location, these can
unnecessarily load values from memory when they don't need to.
Useful vim commands:
%s/ingredients\[\([^\]]*\)\]/ingredients.at(\1)/gc
%s/products\[\([^\]]*\)\]/products.at(\1)/gc
.,$s/\[\(.\)]/.at(\1)/gc
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I've tried to update the Readme, but there are at least a couple of issues.
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