Interpret letrec-values

[pmatos]

Summary

• Teach the interpreter to evaluate letrec-values, whose bindings are in scope for both the binding expressions and the body (enabling recursion and mutual recursion), unlike let-values whose expressions evaluate in the enclosing scope.
• letrec-values reuses the existing LetValues AST node and parseLetValues, distinguished by a new Rec flag; the parser accepts the already-lexed letrec-values keyword.
• The interpreter pushes a fresh environment and fills it in left to right, keeping it live on the stack while the binding expressions and body evaluate, so clauses can refer to earlier and later bindings the way top-level recursive definitions already do.
• Free-variable analysis now also walks the binding expressions (previously only the body), shadowing the bound identifiers for letrec-values but not for let-values, so closures enclosing either form capture the correct variables.

Fixes #8

Test plan

• ctest --preset debug — 14 unit tests pass (adds a letrec-values lexing test)
• nora-lit test/integration — 52 integration tests pass (adds 4 letrec-values .rkt tests: sequential binding, closure over a later binding, mutual reference, multiple-values clause)
• clang-format --dry-run --Werror on changed files — clean
• Debug build is warning-clean (warnings-as-errors)

[codecov]

Codecov Report

❌ Patch coverage is 81.96721% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.41%. Comparing base (1ca9b29) to head (9cbd29c).

Files with missing lines	Patch %	Lines
src/Interpreter.cpp	71.42%	10 Missing ⚠️
src/AST.cpp	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #78      +/-   ##
==========================================
+ Coverage   73.19%   74.41%   +1.22%     
==========================================
  Files          24       24              
  Lines        2108     2146      +38     
  Branches      290      299       +9     
==========================================
+ Hits         1543     1597      +54     
+ Misses        565      549      -16     

Flag	Coverage Δ
integration	74.41% <81.96%> (+1.22%)	⬆️

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[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

[pmatos]

Regarding the Codecov patch-coverage report: the meaningful gap was the new AnalysisFreeVars::visit(LetValues) binding-expression traversal (6 lines, 0%), which no test exercised because none nested a let/letrec-values inside a closure.

Fixed in 9cbd29c.

• Changed: added two integration tests — test/integration/letrec-values4.rkt and test/integration/let-values4.rkt — each a closure enclosing a letrec-values / let-values whose binding expression captures a free variable from the surrounding lambda. These drive free-variable analysis over the binding expressions for both the letrec and let branches.
• Validation: cmake --build --preset debug (warning-clean), ctest --preset debug, and nora-lit test/integration (now 54/54) all green.

The remaining uncovered lines are left intentionally: the bindClause error branches in src/Interpreter.cpp require malformed programs that aren't expressible with the current runtime (only +/-/* are registered, no predicates), and the AST.cpp line is the debug-only LLVM_DUMP_METHOD dump() label. Both Codecov checks were already passing (non-blocking).