Joseph Ferano
5a67cf458a
The first of the three things HANDOFF-x86-redef.md left: a function or a defvar the running process has no symbol for. ELF cannot grow one, so the address is asked for by string at install time -- flan_dev_cell for a cell, flan_dev_global for a global's storage -- and parked in a slot this module defines. The reference side is one new [loc] case and nothing else. [Lslot] loads the slot and answers [Reg (scratch, d)], which is exactly what [Lgot] already did with [Got] where this has [Sym]; every site that reaches a cell already double-loads, so no call site, no place expression and no [sym_loc] caller had to learn a third case. [fnctx.slot] is a second predicate rather than a widened [ext] because they answer different questions -- [ext] says "the host's, reach it through the GOT", [slot] says "nobody's yet, reach it through a slot I filled". It defaults to [fun _ -> None], so the whole-program path emits byte-identical output and the survey goes on being a structural check. flan_reload_install is now a function with a frame rather than a run of loads and stores, because it makes calls and a call on an unaligned stack faults inside glibc's movaps rather than anywhere a reader would look. Its shape is emit_globals_init's, down to owning the null transfer cell no caller hands it. A new global's declared value travels with it: flan_dev_global copies the image onto the allocation the first time the name is interned and ignores it after, which is where "a reload must not reset the state" lives. emit.ml folds that value into an LLVM constant and this file has no folder, so the image is a module-local buffer written by the initialiser lowered as ordinary code -- the same bargain emit_globals_data already documents. Republishing a defconst came free once the rest was there: one store of the new constant into the host's global, which is what emit.ml does. reload-v6.flan is new. v3's [extra] is declared zero, which calloc also gives, so a run-time-new global whose initial value never arrived would still pass; v6's [tuning] is 42 and the host prints 88. test_reload.ml's x86 section now runs all four modules against the same transcript the LLVM path is held to, and the refusal it used to assert is gone.
Flan
A statically typed Lisp for native games and interactive development.
Flan is an experimental, ahead-of-time compiled Lisp for programs that need predictable memory use and a fast edit–run loop. It combines S-expressions, static types, explicit ownership, and a development session that can replace a function in a running program without resetting its state.
It is being built around games, but the interesting part is broader: a compiled language where the running program remains available for inspection, experimentation, and small changes.
In practical terms: you get parentheses, a debugger that would like to have a conversation, and no garbage collector quietly choosing the dramatic moment to join your frame loop.
What it has
- Native compilation through LLVM, plus an in-progress direct x86-64 backend.
- C-like data layout: structs, fixed arrays, pointers, slices, and explicit allocation. There is no garbage collector.
- Owned
VecandMapcontainers, plus checked moves and borrowing-oriented slice operations. - Generics, algebraic unions, enums, macros, packages,
defer, and a C FFI. - Conditions and restarts for recoverable failures and interactive debugging.
- A raylib package and a collection of ported raylib examples.
- Native, WASI, and web build targets. The cross targets are useful but less complete than the native development workflow.
The project is exploratory software, not a stable language release. Some features are deliberately refused while their semantics are still undecided; the compiler aims to say why rather than quietly accepting a partial version. It has opinions, but at least they arrive as error messages.
Quick start
Building requires a current OCaml/Dune toolchain, LLVM/Clang, and the native C toolchain. Raylib is only needed for programs that use the bundled graphics package.
dune build
dune exec ./bin/main.exe -- run web/examples/hello.flan
To build a standalone native executable:
dune exec ./bin/main.exe -- build web/examples/hello.flan -o hello
./hello
The falling-sand demo uses raylib:
dune exec ./bin/main.exe -- run sand.flan
Once you are iterating regularly, put the built executable on your PATH if
you want to use the shorter flan commands shown below.
The live development loop
Start a long-lived development session:
flan dev sand.flan
The program runs normally and publishes a local socket beside the source file. The bundled Emacs mode can attach to it, evaluate expressions in the live process, inspect a stopped program, and recompile a top-level function from the buffer. A body change takes effect on the next call; changing a function's signature is intentionally rejected. The program keeps its state, which is especially nice when you have finally arranged the sand into something almost worth saving.
To set up the mode:
(add-to-list 'load-path "~/path/to/flan/emacs")
(require 'flan-mode)
Then use M-x flan-dev to start and attach, or C-c C-z to attach to a
session started in a terminal. The editor workflow is documented in
emacs/MANUAL.md.
A small example
(defstruct AssetMissing [id i32])
(defn load-asset [id i32] i32
(signal (AssetMissing {.id id}))
100)
(defn asset-or-placeholder [id i32] i32
(restart-case (load-asset id)
(use-placeholder [] -1)))
(defn main [] ()
(handler-bind [(AssetMissing [_] (invoke-restart 'use-placeholder))]
(println (asset-or-placeholder 7))))
Here a missing asset signals a typed condition. The handler chooses a restart, so execution continues with a placeholder instead of requiring error values to be threaded through every caller. See web/examples/restart.flan for a runnable version.
Commands
flan check <file.flan> type-check a program
flan run <file.flan> [args...] build and run it
flan build <file.flan> [-o out] [options] build a native executable
flan dev <file.flan> [-s socket] start a live development session
Useful build options include --debug, --sanitize, --no-bounds-checks,
--x86, and --target=wasm32-wasi|web. run is native-only; cross-built
output should be run with an appropriate WASI runtime or browser. A .wasm
file is not a tiny native executable in a trench coat.
Project map
- web/index.html — language reference and fuller examples.
- spec-memory.md — ownership, containers, and generics.
- spec-conditions.md — conditions, handlers, and restarts.
- emacs/MANUAL.md — the interactive editor workflow.
- docs/BUILT.md — implementation rationale.
- NEXT.md — current work and known limits.
License
Flan is released under the MIT License. Third-party material under
vendor/ is distributed under its own licenses.