Result.hs

-----------------------------------------------------------------------------
-- Copyright 2019, Advise-Me project team. This file is distributed under 
-- the terms of the Apache License 2.0. For more information, see the files
-- "LICENSE.txt" and "NOTICE.txt", which are included in the distribution.
-----------------------------------------------------------------------------
-- |
-- Maintainer  :  bastiaan.heeren@ou.nl
-- Stability   :  provisional
-- Portability :  portable (depends on ghc)
--
-----------------------------------------------------------------------------

module Recognize.Model.Result where

import Data.Semigroup

-- | Describes the possible results of the predicate of a constraint
data Result =
  Success -- ^ The predicate was true
  | Failure -- ^ The predicate was false
  | Unknown -- ^ We don't know whether the predicate is true or false
  deriving (Eq, Show)

instance Semigroup Result where
  Success <> Success = Success
  Success <> r2 = r2
  r1 <> Success = r1
  Unknown <> Unknown = Unknown
  _ <> Failure = Failure
  Failure <>  _ = Failure

instance Monoid Result where
   mempty  = Success
   mappend = (<>)

resultToBool :: Result -> Maybe Bool
resultToBool Success = Just True
resultToBool Failure = Just False
resultToBool Unknown = Nothing

isUnknown :: Result -> Bool
isUnknown Unknown = True
isUnknown _ = False

negate :: Result -> Result
negate Success = Failure
negate Failure = Success
negate Unknown = Unknown