Add eager merge container primitives

[saulshanabrook]

Stack

Draft PR built on top of #881.

This branch includes the commits from that PR until #881 lands, so review should focus on the final commit, Add eager merge container primitives.

What changed

• Adds Maybe and Either container sorts with unwrap/match primitives.
• Adds unstable-if, a Unit-thunk-conditioned primitive that eagerly returns one of two already-built values.
• Registers unstable-if, Maybe match, and Either match in both declaration orders needed by generated egglog programs.
• Adds focused .egg tests for Maybe, Either, UnstableFn, and late registration.

Why

eggcc is moving merge functions away from constructor-producing encodings. These primitives let merge bodies compute eagerly over container values, so generated :merge expressions can return an existing value rather than creating a constructor node only to rewrite it later.

Validation

• cargo build --release
• cargo build --release --bin egglog-experimental in the dependent egglog-experimental worktree
• fish -lc 'cargo build --release' in eggcc
• During development, focused file tests passed for fn, maybe, either, and pair.

[codspeed-hq]

Merging this PR will improve performance by 7.61%

⚡ 1 improved benchmark
✅ 25 untouched benchmarks
⏩ 216 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	tests[repro-665-set-union]	625.2 ms	581 ms	+7.61%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing saulshanabrook:codex/eager-merge-containers (411c991) with main (f0da95b)}

Footnotes

1. 216 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov-commenter]

Codecov Report

❌ Patch coverage is 75.67204% with 181 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.57%. Comparing base (57108da) to head (411c991).
⚠️ Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
src/exec_state.rs	0.00%	66 Missing ⚠️
src/lib.rs	77.15%	53 Missing ⚠️
src/sort/either.rs	80.87%	35 Missing ⚠️
src/sort/maybe.rs	86.58%	22 Missing ⚠️
src/typechecking.rs	89.36%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #918      +/-   ##
==========================================
- Coverage   87.17%   86.57%   -0.61%     
==========================================
  Files          88       90       +2     
  Lines       26106    27019     +913     
==========================================
+ Hits        22759    23392     +633     
- Misses       3347     3627     +280     

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[oflatt]

Just a note, I think maybe and either seem like egglog-experimental type things right?
I think moving egglog-experimental into this code base would make this a lot easier...

[saulshanabrook]

TODO should remove this extra change here

[saulshanabrook]

Just a note, I think maybe and either seem like egglog-experimental type things right?

Yeah that sounds nice! The issue is that we have to inline certain type registration in the fn.rs registration:

    register_maybe_primitives_for_function(eg, self.clone());
    register_if_primitives_for_function(eg, self.clone());
    register_either_primitives_for_function(eg, self.clone());

To move those to experimental, we could add some kind of thing in core to allow registering callbacks here... I think I could do that, in a way that is non specific to unstable function... Would definately be nice to move a bunch of this stuff to experimental I agree! Also to be able to add particular other function registration to other sorts like Map that are in experimental.

I think moving egglog-experimental into this code base would make this a lot easier...

Yeah once all my in flight PRs (besides this one) land in egglog/experimental I will make a PR to see how that looks!

[saulshanabrook]

Closing and replacing with an experimental PR