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OCaml 5.0のEffect handlersをさわってみた

Effect handlersについて調べた時のメモ書きです。 OCamlについては初心者です。

参考文献

• https://v2.ocaml.org/releases/5.0/htmlman/effects.html
• https://github.com/ocamllabs/ocaml-effects-tutorial
• https://qiita.com/hayao0727/items/92b8e71b9305765b3458

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open Effect
open Effect.Deep
open Effect.Shallow

type _ Effect.t += Get: int t
                 | Put: int -> unit t
                 | Exc: string -> unit t

let run_reader (i : int) e =
  try_with e ()

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package monadicDC

import scala.annotation.tailrec

enum Equal[A, B] {
  case EQ[A]() extends Equal[A, A]
  case NE()
}

opaque type Prompt[A] = Int

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:- use_module(library(clpfd)).

piece(_, []).
piece([_ | Frame], [[] | Piece]) :-
    piece(Frame, Piece).
piece([[X | FrameLine] | Frame], [[X | PieceLine] | Piece]) :-
    piece([FrameLine | Frame], [PieceLine | Piece]).

tail([], []).
tail([_ | T], T).

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scala> trait Eff[+R[_], A]
// defined trait Eff

scala> enum Reader[I, A] { case Ask[I]() extends Reader[I, I] }
// defined class Reader

scala> enum Writer[W, A] { case Tell[W](value: W) extends Writer[W, Unit] }
// defined class Writer

scala> def run[A](eff: Eff[Nothing, A]): A = ???

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# 値によって変わる型

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---

## 今日はなすネタ

面白そうなツイートを見つけた

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import os
import re
import time
import picamera
import slack
import RPi.GPIO as GPIO

SERVO_OUT = 2
IMAGE_FILENAME = 'test.jpg'
RECORDING_FILENAME = 'test.h264'                                                                                                                                                                                                             

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{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE DataKinds, PolyKinds #-}
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, FlexibleContexts #-}

module EffAp where

import Control.Concurrent
import Control.Concurrent.Async
import OpenUnion

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package starlight

import akka.actor.Actor
import akka.actor.ActorSystem
import akka.actor.Props
import akka.stream.ActorMaterializer
import akka.stream.scaladsl.FileIO
import akka.stream.scaladsl.Source
import java.awt.RenderingHints
import java.awt.image.BufferedImage