-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | Define Backwards Compatibility Schemes for Arbitrary Data
--   
--   Define Backwards Compatibility Schemes for Arbitrary Data
@package data-compat
@version 0.1.0.2


-- | See <a>http://programmable.computer/compatible.html</a> for a full
--   exposition and worked examples.
module Data.Compat

-- | A class for backwards-compatible data.
class Compat a where {
    
    -- | The predecessor for this type, i.e. the type for the data schema
    --   directly preceeding <tt>a</tt>.
    type family Pred a :: *;
    
    -- | Any additional constraints required to yield data values. Typically
    --   this will be a class that provides a parser.
    type family CompatConstraint a :: * -> Constraint;
    
    -- | A type for wrapping migration results. It is most useful if this type
    --   has <a>Alternative</a> and <a>Monad</a> instances, enabling the use of
    --   <a>getCompatible</a>. <a>Maybe</a> is a good first choice.
    type family CompatF a :: * -> *;
}

-- | How to migrate from a value of the preceeding schema to the current
--   schema.
migrate :: Compat a => Pred a -> CompatF a a
continue :: Compat a => Proxy a -> Maybe (Dict (Compat (Pred a), CompatConstraint a (Pred a), CompatConstraint a ~ CompatConstraint (Pred a), CompatF a ~ CompatF (Pred a)))

-- | Recursively migrate a data value to the most recent schema, if
--   possible.
getCompatible :: forall a. (Compat a, CompatConstraint a a, Alternative (CompatF a), Monad (CompatF a)) => (forall c. (Compat c, CompatConstraint a c) => CompatF a c) -> CompatF a a