-- | This module defines a common type various evaluation machine use to return their results.

{-# LANGUAGE DeriveAnyClass        #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings     #-}
{-# LANGUAGE RankNTypes            #-}
{-# LANGUAGE UndecidableInstances  #-}

module PlutusCore.Evaluation.Result
    ( AsEvaluationFailure (..)
    , evaluationFailure
    , _EvaluationFailureVia
    , EvaluationResult (..)
    , isEvaluationSuccess
    , isEvaluationFailure
    ) where

import PlutusPrelude

import PlutusCore.Pretty

import Control.Lens
import Control.Monad.Except

-- Note that we can't just use 'makeClassyPrisms' for 'EvaluationResult' as that would generate
-- @_EvaluationSuccess@ as well as @_EvaluationFailure@, which would no longer be prismatic error
-- handling: it'd constrain the monad, not the error in it.
--
-- We could define
--
--     data EvaluationFailure = EvaluationFailure
--
-- just for the purpose of using 'makeClassyPrisms' over it, but then it's clearer to write out
-- the class definition manually than to hide it behind a TH function called over a redundant
-- data type name-clashing with the useful 'EvaluationResult'.
-- | A class for viewing errors as evaluation failures (in the sense of Plutus).
class AsEvaluationFailure err where
    _EvaluationFailure :: Prism' err ()

evaluationFailure :: AsEvaluationFailure err => err
evaluationFailure :: err
evaluationFailure = Tagged () (Identity ()) -> Tagged err (Identity err)
forall err. AsEvaluationFailure err => Prism' err ()
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forall t b. AReview t b -> b -> t
# ()

-- | Construct a 'Prism' focusing on the @*EvaluationFailure@ part of @err@ by taking
-- that @*EvaluationFailure@ and
--
-- 1. returning it for the setter part of the prism
-- 2. checking the error for equality with @*EvaluationFailure@ for the opposite direction.
_EvaluationFailureVia :: Eq err => err -> Prism' err ()
_EvaluationFailureVia :: err -> Prism' err ()
_EvaluationFailureVia err
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-- | The parameterized type of results various evaluation engines return.
-- On the PLC side this becomes (via @makeKnown@) either a call to 'Error' or
-- a value of the PLC counterpart of type @a@.
data EvaluationResult a
    = EvaluationSuccess a
    | EvaluationFailure
    deriving (Int -> EvaluationResult a -> ShowS
[EvaluationResult a] -> ShowS
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-- This and the next one are two instances that allow us to write the following:
--
-- >>> import Control.Monad.Error.Lens
-- >>> throwing_ _EvaluationFailure :: EvaluationResult Bool
-- EvaluationFailure
instance AsEvaluationFailure () where
    _EvaluationFailure :: p () (f ()) -> p () (f ())
_EvaluationFailure = p () (f ()) -> p () (f ())
forall a. a -> a
id

instance MonadError () EvaluationResult where
    throwError :: () -> EvaluationResult a
throwError () = EvaluationResult a
forall a. EvaluationResult a
EvaluationFailure

    catchError :: EvaluationResult a
-> (() -> EvaluationResult a) -> EvaluationResult a
catchError EvaluationResult a
EvaluationFailure () -> EvaluationResult a
f = () -> EvaluationResult a
f ()
    catchError EvaluationResult a
x                 () -> EvaluationResult a
_ = EvaluationResult a
x

instance Applicative EvaluationResult where
    pure :: a -> EvaluationResult a
pure = a -> EvaluationResult a
forall a. a -> EvaluationResult a
EvaluationSuccess

    EvaluationSuccess a -> b
f <*> :: EvaluationResult (a -> b)
-> EvaluationResult a -> EvaluationResult b
<*> EvaluationResult a
a = (a -> b) -> EvaluationResult a -> EvaluationResult b
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fmap a -> b
f EvaluationResult a
a
    EvaluationResult (a -> b)
EvaluationFailure   <*> EvaluationResult a
_ = EvaluationResult b
forall a. EvaluationResult a
EvaluationFailure

instance Monad EvaluationResult where
    EvaluationSuccess a
x >>= :: EvaluationResult a
-> (a -> EvaluationResult b) -> EvaluationResult b
>>= a -> EvaluationResult b
f = a -> EvaluationResult b
f a
x
    EvaluationResult a
EvaluationFailure   >>= a -> EvaluationResult b
_ = EvaluationResult b
forall a. EvaluationResult a
EvaluationFailure

instance Alternative EvaluationResult where
    empty :: EvaluationResult a
empty = EvaluationResult a
forall a. EvaluationResult a
EvaluationFailure

    EvaluationSuccess a
x <|> :: EvaluationResult a -> EvaluationResult a -> EvaluationResult a
<|> EvaluationResult a
_ = a -> EvaluationResult a
forall a. a -> EvaluationResult a
EvaluationSuccess a
x
    EvaluationResult a
EvaluationFailure   <|> EvaluationResult a
a = EvaluationResult a
a

instance MonadFail EvaluationResult where
    fail :: String -> EvaluationResult a
fail String
_ = EvaluationResult a
forall a. EvaluationResult a
EvaluationFailure

instance PrettyBy config a => PrettyBy config (EvaluationResult a) where
    prettyBy :: config -> EvaluationResult a -> Doc ann
prettyBy config
config (EvaluationSuccess a
x) = config -> a -> Doc ann
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config a
x
    prettyBy config
_      EvaluationResult a
EvaluationFailure     = Doc ann
"Failure"

instance PrettyClassic a => Pretty (EvaluationResult a) where
    pretty :: EvaluationResult a -> Doc ann
pretty = EvaluationResult a -> Doc ann
forall a ann. PrettyClassic a => a -> Doc ann
prettyClassicDef

-- | Check whether an 'EvaluationResult' is an 'EvaluationSuccess'.
isEvaluationSuccess :: EvaluationResult a -> Bool
isEvaluationSuccess :: EvaluationResult a -> Bool
isEvaluationSuccess = Bool -> Bool
not (Bool -> Bool)
-> (EvaluationResult a -> Bool) -> EvaluationResult a -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. EvaluationResult a -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null

-- | Check whether an 'EvaluationResult' is an 'EvaluationFailure'.
isEvaluationFailure :: EvaluationResult a -> Bool
isEvaluationFailure :: EvaluationResult a -> Bool
isEvaluationFailure = EvaluationResult a -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null