From ad8f9f55ea79a4d587aecc69698808da82de3d62 Mon Sep 17 00:00:00 2001 From: somhairle Date: Tue, 21 Apr 2026 20:40:27 +0800 Subject: 二〇二六年四月二十一日 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- ...\346\233\264\346\216\245\350\277\221delimcc.md" | 95 ++++++++++++++++++++++ 1 file changed, 95 insertions(+) create mode 100644 "source/_posts/\351\232\220\350\227\217\344\270\200\344\272\233OCaml-Effect\347\232\204\346\234\272\345\210\266\357\274\214\350\256\251\345\205\266\350\257\255\346\263\225\345\234\250\347\262\276\347\245\236\344\270\212\346\233\264\346\216\245\350\277\221delimcc.md" (limited to 'source/_posts/隐藏一些OCaml-Effect的机制，让其语法在精神上更接近delimcc.md') diff --git "a/source/_posts/\351\232\220\350\227\217\344\270\200\344\272\233OCaml-Effect\347\232\204\346\234\272\345\210\266\357\274\214\350\256\251\345\205\266\350\257\255\346\263\225\345\234\250\347\262\276\347\245\236\344\270\212\346\233\264\346\216\245\350\277\221delimcc.md" "b/source/_posts/\351\232\220\350\227\217\344\270\200\344\272\233OCaml-Effect\347\232\204\346\234\272\345\210\266\357\274\214\350\256\251\345\205\266\350\257\255\346\263\225\345\234\250\347\262\276\347\245\236\344\270\212\346\233\264\346\216\245\350\277\221delimcc.md" new file mode 100644 index 00000000..e6caefb7 --- /dev/null +++ "b/source/_posts/\351\232\220\350\227\217\344\270\200\344\272\233OCaml-Effect\347\232\204\346\234\272\345\210\266\357\274\214\350\256\251\345\205\266\350\257\255\346\263\225\345\234\250\347\262\276\347\245\236\344\270\212\346\233\264\346\216\245\350\277\221delimcc.md" @@ -0,0 +1,95 @@ +--- +title: 隐藏一些OCaml Effect的机制，让其语法在精神上更接近delimcc +date: 2023-06-28 21:47:16 +tags: [Technique] +--- + + +[delimcc_of_fxhandler这个库](https://github.com/kayceesrk/delimcc_of_fxhandler)在OCaml5的effect handlers上实现了一些delimcc原语(shift/reset, control/prompt这些)： +```ocaml + let p = new_prompt () in + assert ([] = push_prompt p (fun () -> + 1::2::take_subcont p (fun _k -> []))); + assert ([1;2] = push_prompt p (fun () -> + 1::2::take_subcont p (fun k -> push_subcont k []))); + assert (135 = + let p1 = new_prompt () in + let p2 = new_prompt () in + let p3 = new_prompt () in + let pushtwice sk = + sk (fun () -> + sk (fun () -> + shift0 p2 (fun sk2 -> sk2 (fun () -> + sk2 (fun () -> 3))) ())) + in + push_prompt p1 (fun () -> + push_prompt p2 (fun () -> + push_prompt p3 (fun () -> shift0 p1 pushtwice ()) + 10) + 1) + 100); + + print_endline "Success!" +``` + +另外， [avsm这里](https://github.com/avsm/ocaml/commits/effect-syntax)可以看到一些OCaml的Effect Syntax进展。 + +还有 [multi-shot continuations in OCaml](https://github.com/dhil/ocaml-multicont)，在这个仓库里面还讨论了一些有趣的问题，例如，OCaml 编译器和runtime会做出一些假设从而进行一些优化，这些优化在使用multi-shot continutation时是不可取的（或完全错误的）。编译器优化导致错误的一个例子是堆到栈的转换，例如: +```ocaml +(* An illustration of how the heap to stack optimisation is broken. + * This example is adapted from de Vilhena and Pottier (2021). + * file: heap2stack.ml + * compile: ocamlopt -I $(opam var lib)/multicont multicont.cmxa heap2stack.ml + * run: ./a.out *) + +(* We first require a little bit of setup. The following declares an + operation `Twice' which we use to implement multiple returns. *) +type _ Effect.t += Twice : unit Effect.t + +(* The handler `htwice' interprets `Twice' by simply invoking its + continuation twice. *) +let htwice : (unit, unit) Effect.Deep.handler + = { retc = (fun x -> x) + ; exnc = (fun e -> raise e) + ; effc = (fun (type a) (eff : a Effect.t) -> + let open Effect.Deep in + match eff with + | Twice -> Some (fun (k : (a, _) continuation) -> + continue (Multicont.Deep.clone_continuation k) (); + continue k ()) + | _ -> None) } + +(* Now for the interesting stuff. In the code below, the compiler will + perform an escape analysis on the reference `i' and deduce that it + does not escape the local scope, because it is unaware of the + semantics of `perform Twice', hence the optimiser will transform + `i' into an immediate on the stack to save a heap allocation. As a + consequence, the assertion `(!i = 1)' will succeed twice, whereas + it should fail after the second return of `perform Twice'. *) +let heap2stack () = + Effect.Deep.match_with + (fun () -> + let i = ref 0 in + Effect.perform Twice; + i := !i + 1; + Printf.printf "i = %d\n%!" !i; + assert (!i = 1)) + () htwice + +(* The following does not trigger an assertion failure. *) +let _ = heap2stack () + +(* To fix this issue, we can wrap reference allocations in an instance + of `Sys.opaque_identity'. However, this is not really a viable fix + in general, as we may not have access to the client code that + allocates the reference! *) +let heap2stack' () = + Effect.Deep.match_with + (fun () -> + let i = Sys.opaque_identity (ref 0) in + Effect.perform Twice; + i := !i + 1; + Printf.printf "i = %d\n%!" !i; + assert (!i = 1)) + () htwice + +(* The following triggers an assertion failure. *) +let _ = heap2stack' () +``` -- cgit v1.2.3