-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/
-- | Validity typeclass
--
-- Please see README.md
@package validity
@version 0.2.0.0
-- | Validity 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
-- Prime that represents prime integers.
--
-- If you were to completely enforce the invariant that the represented
-- number is a prime, then we could use Numeric.Natural 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 Prime by a newtype Prime =
-- Prime Int. Now we have to maintain the invariant that the
-- Int that we use to represent the prime is in fact positive
-- and a prime.
--
-- The Validity typeclass allows us to specify this invariant
-- (and enables testing via the genvalidity libraries:
-- https://hackage.haskell.org/package/genvalidity):
--
--
-- instance Validity Prime where
-- isValid (Prime n) = isPrime n
--
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
instance (Data.Validity.Validity a, Data.Foldable.Foldable t) => Data.Validity.Validity (t 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 Validity a instance as well, then a
-- isValidFor b should imply isValid a for any
-- b.
--
-- If there is a Validity b instance as well, then a
-- isValidFor b should imply isValid b for any
-- a.
class RelativeValidity a b
isValidFor :: RelativeValidity a b => a -> b -> Bool