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


-- | Validity typeclass
--   
--   Note: There are companion instance packages for this library:
--   
--   <ul>
--   <li><a>validity-text</a></li>
--   <li><a>validity-containers</a></li>
--   </ul>
@package validity
@version 0.3.0.2


-- | <tt>Validity</tt> is used to specify additional invariants upon values
--   that are not enforced by the type system.
--   
--   Let's take an example. Suppose we were to implement a type
--   <tt>Prime</tt> that represents prime integers.
--   
--   If you were to completely enforce the invariant that the represented
--   number is a prime, then we could use <tt>Numeric.Natural</tt> and only
--   store the index of the given prime in the infinite sequence of prime
--   numbers. This is very safe but also very expensive if we ever want to
--   use the number, because we would have to calculcate all the prime
--   numbers until that index.
--   
--   Instead we choose to implement <tt>Prime</tt> by a <tt>newtype Prime =
--   Prime Int</tt>. Now we have to maintain the invariant that the
--   <tt>Int</tt> that we use to represent the prime is in fact positive
--   and a prime.
--   
--   The <tt>Validity</tt> typeclass allows us to specify this invariant
--   (and enables testing via the <tt>genvalidity</tt> libraries:
--   <a>https://hackage.haskell.org/package/genvalidity</a> ):
--   
--   <pre>
--   instance Validity Prime where
--       isValid (Prime n) = isPrime n
--   </pre>
module Data.Validity

-- | A class of types that have additional invariants defined upon them
--   that aren't enforced by the type system
class Validity a
isValid :: Validity a => a -> Bool

-- | Construct a valid element from an unchecked element
constructValid :: Validity a => a -> Maybe a

-- | Construct a valid element from an unchecked element, throwing
--   <a>error</a> on invalid elements.
constructValidUnsafe :: (Show a, Validity a) => a -> a
instance (Data.Validity.Validity a, Data.Validity.Validity b) => Data.Validity.Validity (a, b)
instance (Data.Validity.Validity a, Data.Validity.Validity b, Data.Validity.Validity c) => Data.Validity.Validity (a, b, c)
instance Data.Validity.Validity a => Data.Validity.Validity [a]
instance Data.Validity.Validity a => Data.Validity.Validity (GHC.Base.Maybe a)


-- | Relative validity
module Data.RelativeValidity

-- | A class of types that have additional invariants defined upon them
--   that aren't enforced by the type system
--   
--   If there is a <tt>Validity a</tt> instance as well, then <tt>a
--   <a>isValidFor</a> b</tt> should imply <tt>isValid a</tt> for any
--   <tt>b</tt>.
--   
--   If there is a <tt>Validity b</tt> instance as well, then <tt>a
--   <a>isValidFor</a> b</tt> should imply <tt>isValid b</tt> for any
--   <tt>a</tt>.
class RelativeValidity a b
isValidFor :: RelativeValidity a b => a -> b -> Bool