validdata.hs

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-- | Capturing data that can either be valid or invalid.
module Language.Atom.Common.ValidData
  ( ValidData
  , validData
  , getValidData
  , whenValid
  , whenInvalid
  ) where

import Language.Atom

-- | 'ValidData' captures the data and its validity condition.
--   'ValidData' is abstract to prevent rules from using invalid data.
data ValidData a = ValidData a (Term Bool)

-- | Create 'ValidData' given the data and validity condition.
validData :: a -> Term Bool -> ValidData a
validData = ValidData 

-- | Get a valid data.  Action is disabled if data is invalid.
getValidData :: ValidData a -> Action a
getValidData (ValidData a v) = when v >> return a

-- | Action enabled if 'ValidData' is valid.
whenValid :: ValidData a -> Action ()
whenValid (ValidData _ v) = when v

-- | Action enabled if 'ValidData' is not valid.
whenInvalid :: ValidData a -> Action ()
whenInvalid (ValidData _ v) = when $ inv v