How it works

How it works

main.sl ──loader──> packages ──lexer/parser──> ASTs ──codegen──> main.gen.c ──cc──> ./main

1. Loader (src/loader.c) — resolves imports (local directory, native package, stdlib, then slang.project pins), scans package directories for .sl files (in deterministic sorted order), merges them per package, and detects cycles via canonical paths.
2. Lexer (src/lexer.c) — tokenizes source into identifiers, keywords, literals, and operators.
3. Parser (src/parser.c) — recursive-descent parser producing an AST (src/ast.h).
4. Code generator (src/codegen/) — walks the ASTs, performs type inference and semantic checks (including pub enforcement), and emits readable C. The runtime in runtime/ (GC, scheduler, pool, containers, native packages) is real C, spliced into every generated file so the binary stays self-contained. Split by concern: core.c, infer.c, expr.c/stmt.c, program.c, liveness.c (GC safepoint roots), and native.c (NatSig dispatch). internal.h holds the shared CG struct.

Native-package signatures live under src/codegen/pkg_<name>/. Their C runtimes are runtime/sl_<name>.c. json uses dispatch.c because decode/encode are generic over the target type. Adding a fixed-signature package is a pkg_<name>/ directory, a runtime/sl_<name>.c file, and one line in loader.c.

1. Driver (src/main.c) — glues it together and shells out to cc. Because GCC/Clang compile the generated C, you get their full optimizer for free.

Inspect what slang generates:

./slangc examples/hello/main.sl --emit-c && cat main.gen.c

Memory management

Compiled programs embed a precise mark-sweep collector (runtime/sl_gc.c). Allocations go through sl_gc_alloc. main() registers the thread, starts the worker pool, and switches into the main task. There is no libgc dependency.

What this means in practice:

• No manual memory management in slang; no leaks from string churn.
• Collection is tracing (mark-and-sweep), so reference cycles are collected — unlike refcounting.
• Cost: stop-the-world pauses. The allocator still serializes on a mutex (batched); that is the current throughput ceiling.
• Every pool worker is registered with the collector. A collection stops the world, walks safepoint roots, the run queue, parked tasks, and (for async-preempted tasks) a conservative stack scan.

Project layout

src/
  common.h       allocation helpers, growable string buffer, file I/O
  loader.h/.c    package discovery, merging, cycle detection
  lexer.h/.c     tokenizer
  ast.h          AST node definitions
  parser.h/.c    recursive-descent parser
  rtpath.h/.c    locate runtime/ next to slangc
  codegen.h      public codegen API (one function: codegen_program)
  codegen/       type checking + C emission
  main.c         driver: flags, invokes cc
runtime/       real C runtime spliced into generated programs
  sl_core.c sl_gc.c sl_containers.c sl_sched.c sl_pool.c
  sl_time.c sl_net.c sl_tls.c sl_json.c sl_proc.c sl_fs.c
stdlib/        slang-source packages (`import "http"`, `import "byteutil"`;
             `import "log"` is a native package — no source files)
examples/      one directory per example program
tests/         language tests plus tests/runtime/ (no slangc)
Makefile       build/test/clean