unikernel/duniverse/ocaml-caqti/caqti/lib-platform/stream.ml

@@ -0,0 +1,84 @@
+(* Copyright (C) 2018--2019  Petter A. Urkedal <paurkedal@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version, with the LGPL-3.0 Linking Exception.
+ *
+ * This library is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * and the LGPL-3.0 Linking Exception along with this library.  If not, see
+ * <http://www.gnu.org/licenses/> and <https://spdx.org>, respectively.
+ *)
+
+open Caqti_stream_sig
+
+module type FIBER = sig
+  type +'a t
+
+  module Infix : sig
+    val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
+    val (>|=) : 'a t -> ('a -> 'b) -> 'b t
+  end
+
+  val return : 'a -> 'a t
+end
+
+module Make(Fiber : FIBER) : S with type 'a fiber := 'a Fiber.t = struct
+  open Fiber.Infix
+
+  let (>>=?) res_future f =
+    res_future >>= function
+    | Ok a -> f a
+    | Error _ as r -> Fiber.return r
+
+  let (>|=?) res_future f =
+    res_future >>= function
+    | Ok a -> Fiber.return @@ Ok (f a)
+    | Error _ as r -> Fiber.return r
+
+  type ('a, 'err) t = unit -> ('a, 'err) node Fiber.t
+  and ('a, 'err) node =
+    | Nil
+    | Error of 'err
+    | Cons of 'a * ('a, 'err) t
+
+  let rec fold ~f t state =
+    t () >>= function
+    | Nil -> Fiber.return (Ok state)
+    | Error err -> Fiber.return (Error err : ('a, 'err) result)
+    | Cons (a, t') -> fold ~f t' (f a state)
+
+  let rec fold_s ~f t state =
+    t () >>= function
+    | Nil -> Fiber.return (Ok state)
+    | Error err -> Fiber.return (Error (`Congested err) : ('a, 'err) result)
+    | Cons (a, t') -> f a state >>=? fold_s ~f t'
+
+  let rec iter_s ~f t =
+    t () >>= function
+    | Nil -> Fiber.return (Ok ())
+    | Error err -> Fiber.return (Error (`Congested err) : ('a, 'err) result)
+    | Cons (a, t') -> f a >>=? fun () -> iter_s ~f t'
+
+  let to_rev_list t = fold ~f:List.cons t []
+
+  let to_list t = to_rev_list t >|=? List.rev
+
+  let rec of_list l =
+    fun () -> match l with
+    | [] -> Fiber.return Nil
+    | hd::tl -> Fiber.return (Cons (hd, (of_list tl)))
+
+  let rec map_result ~f xs () =
+    xs () >|= function
+     | Cons (x, xs') ->
+        (match f x with
+         | Result.Ok y -> Cons (y, map_result ~f xs')
+         | Result.Error e -> Error e)
+     | Nil | Error _ as r -> r
+end