jolt could call C (foreign-fn -> foreign-procedure) but C could not call back
into jolt, which GTK signals (and any callback-taking C API) require. Add the
inverse: jolt.ffi/foreign-callable wraps a jolt fn as a C-callable function
pointer, mirroring the foreign-fn pipeline.
A new jolt.ffi/__ccallable special form carries the fn as a child expression
(analyzed + walked by the passes; ir.clj gains an :ffi-callable arm in both
child walks) plus literal arg/ret type keywords. The back end lowers it to a
locked Chez foreign-callable and returns its entry-point address as a jolt
pointer; host/chez/ffi.ss registers the code object so the collector keeps it,
and free-callable unlocks it. :collect-safe emits the convention that
reactivates the thread on entry, for callbacks fired while it is parked in a
:blocking call (a GTK main loop).
Test: ffi-binding-test.ss sorts an int array through libc qsort with a jolt
comparator (C -> jolt -> C). Re-minted seed.
read-bytes/write-bytes go through UTF-8 (with a latin1 fallback), which mangles
arbitrary binary — gzip payloads, TLS records, any non-text body. An HTTP client
moving bytes between jolt byte-arrays and foreign socket/zlib/OpenSSL buffers
needs byte-exact transfer. read-array returns a fresh byte-array of n bytes from
foreign memory; write-array copies a byte-array's bytes into a pointer. Test
covers a round-trip preserving high bytes (200, 255).
A jolt library can now bind its own native dependencies and expose a Clojure API
over them — no jolt built-in required. This is the foundation for moving the
http-client / db / adapter functionality out of the host and into real libraries.
- jolt.ffi/foreign-fn (sugar: defcfn) is a compiler special form: a compile-time
-typed C signature lowers to a real Chez foreign-procedure (analyzer :ffi-fn ->
backend foreign-procedure), so calls are typed and marshaled, not eval'd.
- host/chez/ffi.ss provides the rest under jolt.ffi: load-library, alloc/free,
read/write/sizeof, ptr<->string, null/null?. Loaded after the loader snapshot
so a library's (require '[jolt.ffi]) still loads the macro side.
- Types: int/uint/long/ulong/int64/uint64/size_t/ssize_t/iptr/uptr/double/float/
pointer/string/void/uint8/char.
Validated end to end: a pure-Clojure file binds libc (getpid/strlen/abs) and
libsqlite3 (open/prepare/step/column/finalize over out-param pointers) and runs a
query. Gate test test/chez/ffi-binding-test.ss (make ffi); selfhost holds.
