C Codegen Backend

LOGOS can now compile to C. compile_to_c() produces a single self-contained .c file with an embedded runtime — no external dependencies, compiles with gcc -O2.

The C runtime includes:

  • Seq_i64, Seq_bool, Seq_str — dynamic arrays with 1-based indexing
  • Map_i64_i64 — open-addressing hash map
  • String helpers — logos_concat, logos_substr, logos_parseInt
  • IO — printf-based Show implementation

C keyword escaping handles collisions: variables named int, double, char, void, etc. get a logos_ prefix via escape_c_ident(). The CContext::resolve() method applies escaping at a single point for all name lookups.

Supported: integers, floats, booleans, strings, sequences, maps, sets, control flow, functions, recursion.

Not supported: CRDTs, async, zones, networking, polymorphism, closures, structs, enums, Escape blocks.

Constant Propagation

A new optimizer pass (optimize/propagate.rs) performs forward substitution of immutable constants. Given:

Let x be 5.
Let y be x + 3.
Show y.

After constant propagation, x is substituted into the expression for y, enabling further folding by the existing constant folder. The pipeline order is: fold → propagate → dce.

Safety: the pass skips substitution inside Index and Slice expressions to preserve swap and vec-fill pattern detection in the codegen.

334 New E2E Tests

  • 16 Rust codegen mirror files (181 tests) — every interpreter-only feature now also tested through the Rust codegen pipeline: primitives, variables, expressions, comparisons, logical operators, control flow, iteration, functions, collections, maps, sets, tuples, types, structs, enums, edge cases
  • e2e_codegen_gaps.rs (64 tests) — floats, modulo, options, nothing, collection type combos, struct/enum patterns, control flow, functions, escape blocks, strings
  • e2e_codegen_optimization.rs (15 tests) — TCO, constant propagation, DCE, vec-fill, swap, fold, index simplification
  • e2e_interpreter_gaps.rs (60 tests) — interpreter counterparts for gap coverage
  • e2e_interpreter_optimization.rs (14 tests) — interpreter counterparts for optimization correctness

Bug Fixes

  1. For-range guard for complex expressions — While i is at most length of items previously produced _ in generated Rust because codegen_expr_simple couldn't handle the length of expression. Added is_simple_expr() guard to bail out when the limit is too complex.
  1. For-range post-loop value for empty loops — While x < 5 with x = 10 previously set x = 5 after the empty loop. Now uses max(start, limit) for exclusive and max(start, limit + 1) for inclusive bounds.
  1. Vec-fill pattern relaxed mutability — Let items be a new Seq of Bool (without explicit mutable) now matches the vec-fill optimization. The pattern check was too strict about mutability annotations.
  1. C codegen missing Set variants — SetI64 and SetStr were not handled in c_type_str(), causing a match failure.
  1. Interpreter float comparison — apply_comparison now handles Float-Float, Int-Float, and Float-Int comparisons instead of falling through to a default case.