{- |
   Module      : Text.Pandoc.Readers.ODT.Generic.Fallible
   Copyright   : Copyright (C) 2015 Martin Linnemann
   License     : GNU GPL, version 2 or above

   Maintainer  : Martin Linnemann <theCodingMarlin@googlemail.com>
   Stability   : alpha
   Portability : portable

Data types and utilities representing failure. Most of it is based on the
"Either" type in its usual configuration (left represents failure).

In most cases, the failure type is implied or required to be a "Monoid".

The choice of "Either" instead of a custom type makes it easier to write
compatible instances of "ArrowChoice".
-}

-- We export everything
module Text.Pandoc.Readers.ODT.Generic.Fallible where

-- | Default for now. Will probably become a class at some point.
type Failure = ()

type Fallible a = Either Failure a


--
maybeToEither :: Maybe a -> Fallible a
maybeToEither :: forall a. Maybe a -> Fallible a
maybeToEither (Just a
a) = forall a b. b -> Either a b
Right a
a
maybeToEither Maybe a
Nothing  = forall a b. a -> Either a b
Left  ()

--
eitherToMaybe :: Either _l a -> Maybe a
eitherToMaybe :: forall _l a. Either _l a -> Maybe a
eitherToMaybe (Left  _l
_) = forall a. Maybe a
Nothing
eitherToMaybe (Right a
a) = forall a. a -> Maybe a
Just a
a

-- | > recover a === either (const a) id
recover :: a -> Either _f a -> a
recover :: forall a _f. a -> Either _f a -> a
recover a
a (Left  _f
_) = a
a
recover a
_ (Right a
a) = a
a

-- | I would love to use 'fail'. Alas, 'Monad.fail'...
failWith :: failure -> Either failure _x
failWith :: forall a b. a -> Either a b
failWith failure
f = forall a b. a -> Either a b
Left failure
f

--
failEmpty :: (Monoid failure) => Either failure _x
failEmpty :: forall failure _x. Monoid failure => Either failure _x
failEmpty = forall a b. a -> Either a b
failWith forall a. Monoid a => a
mempty

--
succeedWith :: a -> Either _x a
succeedWith :: forall a _x. a -> Either _x a
succeedWith = forall a b. b -> Either a b
Right

--
collapseEither :: Either failure (Either failure x)
               -> Either failure x
collapseEither :: forall failure x.
Either failure (Either failure x) -> Either failure x
collapseEither (Left failure
f         ) = forall a b. a -> Either a b
Left failure
f
collapseEither (Right (Left  failure
f)) = forall a b. a -> Either a b
Left failure
f
collapseEither (Right (Right x
x)) = forall a b. b -> Either a b
Right x
x

-- | If either of the values represents a  non-error, the result is a
-- (possibly combined) non-error. If both values represent an error, an error
-- is returned.
chooseMax :: (Monoid a, Monoid b) => Either a b -> Either a b -> Either a b
chooseMax :: forall a b.
(Monoid a, Monoid b) =>
Either a b -> Either a b -> Either a b
chooseMax = forall a b.
Monoid a =>
(b -> b -> b) -> Either a b -> Either a b -> Either a b
chooseMaxWith forall a. Monoid a => a -> a -> a
mappend

-- | If either of the values represents a non-error, the result is a
-- (possibly combined) non-error. If both values represent an error, an error
-- is returned.
chooseMaxWith :: (Monoid a) => (b -> b -> b)
                            -> Either a b
                            -> Either a b
                            -> Either a b
chooseMaxWith :: forall a b.
Monoid a =>
(b -> b -> b) -> Either a b -> Either a b -> Either a b
chooseMaxWith b -> b -> b
(><) (Right b
a) (Right b
b) = forall a b. b -> Either a b
Right forall a b. (a -> b) -> a -> b
$ b
a b -> b -> b
>< b
b
chooseMaxWith  b -> b -> b
_   (Left  a
a) (Left  a
b) = forall a b. a -> Either a b
Left  forall a b. (a -> b) -> a -> b
$ a
a forall a. Monoid a => a -> a -> a
`mappend` a
b
chooseMaxWith  b -> b -> b
_   (Right b
a)     Either a b
_     = forall a b. b -> Either a b
Right b
a
chooseMaxWith  b -> b -> b
_       Either a b
_     (Right b
b) = forall a b. b -> Either a b
Right b
b


-- | Class of containers that can escalate contained 'Either's.
-- The word "Vector" is meant in the sense of a disease transmitter.
class ChoiceVector v where
  spreadChoice :: v (Either f a) -> Either f (v a)

instance ChoiceVector ((,) a) where
  spreadChoice :: forall f a. (a, Either f a) -> Either f (a, a)
spreadChoice (a
_, Left  f
f) = forall a b. a -> Either a b
Left  f
f
  spreadChoice (a
x, Right a
y) = forall a b. b -> Either a b
Right (a
x,a
y)
  -- Wasn't there a newtype somewhere with the elements flipped?

-- | Wrapper for a list. While the normal list instance of 'ChoiceVector'
-- fails whenever it can, this type will never fail.
newtype SuccessList a = SuccessList { forall a. SuccessList a -> [a]
collectNonFailing :: [a] }
  deriving ( SuccessList a -> SuccessList a -> Bool
forall a. Eq a => SuccessList a -> SuccessList a -> Bool
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
/= :: SuccessList a -> SuccessList a -> Bool
$c/= :: forall a. Eq a => SuccessList a -> SuccessList a -> Bool
== :: SuccessList a -> SuccessList a -> Bool
$c== :: forall a. Eq a => SuccessList a -> SuccessList a -> Bool
Eq, SuccessList a -> SuccessList a -> Bool
SuccessList a -> SuccessList a -> Ordering
SuccessList a -> SuccessList a -> SuccessList a
forall a.
Eq a
-> (a -> a -> Ordering)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> a)
-> (a -> a -> a)
-> Ord a
forall {a}. Ord a => Eq (SuccessList a)
forall a. Ord a => SuccessList a -> SuccessList a -> Bool
forall a. Ord a => SuccessList a -> SuccessList a -> Ordering
forall a. Ord a => SuccessList a -> SuccessList a -> SuccessList a
min :: SuccessList a -> SuccessList a -> SuccessList a
$cmin :: forall a. Ord a => SuccessList a -> SuccessList a -> SuccessList a
max :: SuccessList a -> SuccessList a -> SuccessList a
$cmax :: forall a. Ord a => SuccessList a -> SuccessList a -> SuccessList a
>= :: SuccessList a -> SuccessList a -> Bool
$c>= :: forall a. Ord a => SuccessList a -> SuccessList a -> Bool
> :: SuccessList a -> SuccessList a -> Bool
$c> :: forall a. Ord a => SuccessList a -> SuccessList a -> Bool
<= :: SuccessList a -> SuccessList a -> Bool
$c<= :: forall a. Ord a => SuccessList a -> SuccessList a -> Bool
< :: SuccessList a -> SuccessList a -> Bool
$c< :: forall a. Ord a => SuccessList a -> SuccessList a -> Bool
compare :: SuccessList a -> SuccessList a -> Ordering
$ccompare :: forall a. Ord a => SuccessList a -> SuccessList a -> Ordering
Ord, Int -> SuccessList a -> ShowS
forall a. Show a => Int -> SuccessList a -> ShowS
forall a. Show a => [SuccessList a] -> ShowS
forall a. Show a => SuccessList a -> String
forall a.
(Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
showList :: [SuccessList a] -> ShowS
$cshowList :: forall a. Show a => [SuccessList a] -> ShowS
show :: SuccessList a -> String
$cshow :: forall a. Show a => SuccessList a -> String
showsPrec :: Int -> SuccessList a -> ShowS
$cshowsPrec :: forall a. Show a => Int -> SuccessList a -> ShowS
Show )

instance ChoiceVector SuccessList  where
  spreadChoice :: forall f a. SuccessList (Either f a) -> Either f (SuccessList a)
spreadChoice = forall a b. b -> Either a b
Right forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a. [a] -> SuccessList a
SuccessList forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr forall {a} {a}. Either a a -> [a] -> [a]
unTagRight [] forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a. SuccessList a -> [a]
collectNonFailing
    where unTagRight :: Either a a -> [a] -> [a]
unTagRight (Right a
x) = (a
xforall a. a -> [a] -> [a]
:)
          unTagRight Either a a
_         = forall a. a -> a
id