I've been saying for a while[1][2][3] that adding extra abstractions makes
things harder for newcomers, and adding new notations doubly so. And then
I notice this DSL in my own backyard. Makes me feel like a hypocrite.
[1] https://news.ycombinator.com/item?id=13565743#13570092
[2] https://lobste.rs/s/to8wpr/configuration_files_are_canary_warning
[3] https://lobste.rs/s/mdmcdi/little_languages_by_jon_bentley_1986#c_3miuf2
The implementation of the DSL was also highly hacky:
a) It was happening in the tangle/ tool, but was utterly unrelated to tangling
layers.
b) There were several persnickety constraints on the different kinds of
lines and the specific order they were expected in. I kept finding bugs
where the translator would silently do the wrong thing. Or the error messages
sucked, and readers may be stuck looking at the generated code to figure
out what happened. Fixing error messages would require a lot more code,
which is one of my arguments against DSLs in the first place: they may
be easy to implement, but they're hard to design to go with the grain of
the underlying platform. They require lots of iteration. Is that effort
worth prioritizing in this project?
On the other hand, the DSL did make at least some readers' life easier,
the ones who weren't immediately put off by having to learn a strange syntax.
There were fewer quotes to parse, fewer backslash escapes.
Anyway, since there are also people who dislike having to put up with strange
syntaxes, we'll call that consideration a wash and tear this DSL out.
---
This commit was sheer drudgery. Hopefully it won't need to be redone with
a new DSL because I grow sick of backslashes.
I've extracted it into a separate binary, independent of my Mu prototype.
I also cleaned up my tracing layer to be a little nicer. Major improvements:
- Realized that incremental tracing really ought to be the default.
And to minimize printing traces to screen.
- Finally figured out how to combine layers and call stack frames in a
single dimension of depth. The answer: optimize for the experience of
`browse_trace`. Instructions occupy a range of depths based on their call
stack frame, and minor details of an instruction lie one level deeper
in each case.
Other than that, I spent some time adjusting levels everywhere to make
`browse_trace` useful.
I've been working on this slowly over several weeks, but it's too hard
to support 0 as the null value for addresses. I constantly have to add
exceptions for scalar value corresponding to an address type (now
occupying 2 locations). The final straw is the test for 'reload':
x:num <- reload text
'reload' returns an address. But there's no way to know that for
arbitrary instructions.
New plan: let's put this off for a bit and first create support for
literals. Then use 'null' instead of '0' for addresses everywhere. Then
it'll be easy to just change what 'null' means.
Clean up how we reclaim local scopes.
It used to work like this (commit 3216):
1. Update refcounts of products after every instruction, EXCEPT:
a) when instruction is a non-primitive and the callee starts with
'local-scope' (because it's already not decremented in 'return')
OR:
b) when instruction is primitive 'next-ingredient' or
'next-ingredient-without-typechecking', and its result is saved to a
variable in the default space (because it's already incremented at
the time of the call)
2. If a function starts with 'local-scope', force it to be reclaimed
before each return. However, since locals may be returned, *very
carefully* don't reclaim those. (See the logic in the old `escaping`
and `should_update_refcount` functions.)
However, this approach had issues. We needed two separate commands for
'local-scope' (reclaim locals on exit) and 'new-default-space'
(programmer takes charge of reclaiming locals). The hard-coded
reclamation duplicated refcounting logic. In addition to adding
complexity, this implementation failed to work if a function overwrites
default-space after setting up a local-scope (the old default-space is
leaked). It also fails in the presence of continuations. Calling a
continuation more than once was guaranteed to corrupt memory (commit
3986).
After this commit, reclaiming local scopes now works like this:
Update refcounts of products for every PRIMITIVE instruction.
For non-primitive instructions, all the work happens in the `return`
instruction:
increment refcount of ingredients to `return`
(unless -- one last bit of ugliness -- they aren't saved in the
caller)
decrement the refcount of the default-space
use existing infrastructure for reclaiming as necessary
if reclaiming default-space, first decrement refcount of each
local
again, use existing infrastructure for reclaiming as necessary
This commit (finally!) completes the bulk[1] of step 2 of the plan in
commit 3991. It was very hard until I gave up trying to tweak the
existing implementation and just test-drove layer 43 from scratch.
[1] There's still potential for memory corruption if we abuse
`default-space`. I should probably try to add warnings about that at
some point (todo in layer 45).
Periodic cleanup to replace 'reply' with 'return' everywhere in the
repo.
I use 'reply' for students to help reinforce the metaphor of function
calls as being like messages through a pipe. But that causes 'reply' to
get into my muscle memory when writing Mu code for myself, and I worry
that that makes Mu seem unnecessarily alien to anybody reading on
Github.
Perhaps I should just give it up? I'll try using 'return' with my next
student.
Kartik Agaram