= 1 + (raise (Foo 3)) let r = try f () with Foo i -> i + 1 val r : int = 4 effect Foo : int -> int let f () = 1 + (perform (Foo 3)) 4 let r = try f () with effect (Foo i) k -> continue k (i + 1) val r : int = 5 fiber — lightweight stack

bytes • No unnecessary closure allocation costs unlike CPS • One-shot delimited continuations • Simplifies reasoning about resources - sockets, locks, etc. • Handlers —> Linked-list of fibers Implementation handle / continue handler sp call chain reference

chain reference • Fibers: Heap allocated, dynamically resized stacks • ~10s of bytes • No unnecessary closure allocation costs unlike CPS • One-shot delimited continuations • Simplifies reasoning about resources - sockets, locks, etc. • Handlers —> Linked-list of fibers

start program C call handle OCaml callback C call C C 1. Stack overflow checks for OCaml functions • Simple static analysis eliminates many checks 2. FFI calls are more expensive due to stack switching • Specialise for calls which {allocate / pass arguments on stack / do neither}

alt-ergo-parameter_smallest_divisor alt-ergo-carte_autorisee_3 alt-ergo-parameter_relabel alt-ergo-OBF__ggjj_2 alt-ergo-parameter_def alt-ergo-parameter_def alt-ergo-OBF__yyll_1 alt-ergo-bbvv_351 alt-ergo-controler_carte_13 alt-ergo-div2_sub alt-ergo-parameter_def alt-ergo-ccgg_2055 alt-ergo-parameter_def alt-ergo-parameter_inverse_in_place alt-ergo-ccgg_1759 alt-ergo-parameter_def alt-ergo-induction_step alt-ergo-ccgg_1618 alt-ergo-ccgg_219 alt-ergo-advance_automaton_25 alt-ergo-nsec_sum_higher_than_1s alt-ergo-fill_assert_39_Alt-Ergo bdd chameneos-async chameneos-lwt cohttp-lwt core_micro cpdf-merge cpdf-reformat cpdf-squeeze cpdf-transform frama-c-deflate frama-c-idct js_of_ocaml jsontrip-sample kb kb-no-exc lexifi-g2pp menhir-fancy menhir-sql menhir-standard minilight numal-durand-kerner-aberth numal-fft numal-k-means numal-levinson-durbin numal-lu-decomposition numal-naive-multilayer numal-qr-decomposition numal-rnd_access numal-simple_access patdiff sauvola-contrast sequence sequence-cps setrip setrip-smallbuf thread-ring-async-pipe thread-ring-lwt-mvar thread-ring-lwt-stream thread-sleep-async thread-sleep-lwt valet-async valet-lwt ydump-sample 4.02.2+effects 4.02.2+vanilla Normalised time (lower is better)

alt-ergo-parameter_smallest_divisor alt-ergo-carte_autorisee_3 alt-ergo-parameter_relabel alt-ergo-OBF__ggjj_2 alt-ergo-parameter_def alt-ergo-parameter_def alt-ergo-OBF__yyll_1 alt-ergo-bbvv_351 alt-ergo-controler_carte_13 alt-ergo-div2_sub alt-ergo-parameter_def alt-ergo-ccgg_2055 alt-ergo-parameter_def alt-ergo-parameter_inverse_in_place alt-ergo-ccgg_1759 alt-ergo-parameter_def alt-ergo-induction_step alt-ergo-ccgg_1618 alt-ergo-ccgg_219 alt-ergo-advance_automaton_25 alt-ergo-nsec_sum_higher_than_1s alt-ergo-fill_assert_39_Alt-Ergo bdd chameneos-async chameneos-lwt cohttp-lwt core_micro cpdf-merge cpdf-reformat cpdf-squeeze cpdf-transform frama-c-deflate frama-c-idct js_of_ocaml jsontrip-sample kb kb-no-exc lexifi-g2pp menhir-fancy menhir-sql menhir-standard minilight numal-durand-kerner-aberth numal-fft numal-k-means numal-levinson-durbin numal-lu-decomposition numal-naive-multilayer numal-qr-decomposition numal-rnd_access numal-simple_access patdiff sauvola-contrast sequence sequence-cps setrip setrip-smallbuf thread-ring-async-pipe thread-ring-lwt-mvar thread-ring-lwt-stream thread-sleep-async thread-sleep-lwt valet-async valet-lwt ydump-sample 4.02.2+effects 4.02.2+vanilla Normalised time (lower is better) 4.02.2+effects ~5.4% slower

t -> (unit -> 'a option) *) let to_gen (type a) (t : a t) = let module M = struct effect Next : a -> unit end in let open M in let step = ref (fun () -> assert false) in let first_step () = try iter (fun x -> perform (Next x)) t; None with effect (Next v) k -> step := continue k; Some v in step := first_step; fun () -> !step () let rec iter f = function | Leaf -> () | Node (l, x, r) -> iter f l; f x; iter f r type 'a t = | Leaf | Node of 'a t * 'a * 'a t