{-# LANGUAGE DataKinds #-}
module Test where

import Data.WorldPeace (OpenUnion, openUnionLift, relaxOpenUnion)
import Data.Bifunctor (first)

data ErrorOne = ErrorOne
data ErrorTwo = ErrorTwo Int
data ErrorThree = ErrorThree String

checkOne :: Int -> Either (OpenUnion '[ErrorOne]) Int
checkOne x = case x of
    1 -> Left $ openUnionLift ErrorOne
    otherwise -> Right x

checkTwo :: Int -> Either (OpenUnion '[ErrorOne, ErrorTwo]) Int
checkTwo x = case x of
    2 -> Left $ openUnionLift ErrorOne
    3 -> Left $ openUnionLift $ ErrorTwo 3
    otherwise -> Right x

checkThree :: Int -> Either (OpenUnion '[ErrorThree]) Int
checkThree x = case x of
    4 -> Left $ openUnionLift $ ErrorThree "error"
    otherwise -> Right x

checkAll :: Int -> Either (OpenUnion '[ErrorOne, ErrorTwo, ErrorThree]) Int
checkAll x = do
    a <- first (relaxOpenUnion) $ checkOne x
    b <- first (relaxOpenUnion) $ checkTwo a
    c <- first (relaxOpenUnion) $ checkThree b
    pure b