diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2016 Tom Sydney Kerckhove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/Setup.hs b/Setup.hs
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/src/Data/Validity.hs b/src/Data/Validity.hs
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--- /dev/null
+++ b/src/Data/Validity.hs
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+{-# LANGUAGE FlexibleInstances #-}
+
+{-|
+
+ @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
+    ( Validity(..)
+    ) where
+
+
+-- | A class of types that have additional invariants defined upon them
+-- that aren't enforced by the type system
+class Validity a where
+    isValid :: a -> Bool
+
+-- | Any @Foldable@ of things that can be checked for validity can be checked
+-- for validity
+--
+-- This includes lists, which means that the empty list is considered valid.
+-- If the empty list should not be considered valid as part of your custom data
+-- type, make sure to write a custom @Validity instance@
+--
+-- This also includes @Maybe@:
+-- It makes sense to assume that 'Nothing' is valid.
+-- If Nothing wasn't valid, you wouldn't have used a Maybe
+-- in the datastructure.
+instance (Validity a, Foldable t) => Validity (t a) where
+    isValid = all isValid
+
diff --git a/validity.cabal b/validity.cabal
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--- /dev/null
+++ b/validity.cabal
@@ -0,0 +1,24 @@
+name:                validity
+version:             0.1.0.0
+synopsis:            Validity typeclass
+description:         Please see README.md
+homepage:            https://github.com/NorfairKing/validity#readme
+license:             MIT
+license-file:        LICENSE
+author:              Tom Sydney Kerckhove
+maintainer:          syd.kerckhove@gmail.com
+copyright:           Copyright: (c) 2016 Tom Sydney Kerckhove
+category:            Web
+build-type:          Simple
+-- extra-source-files:
+cabal-version:       >=1.10
+
+library
+  hs-source-dirs:      src
+  exposed-modules:     Data.Validity
+  build-depends:       base >= 4.7 && < 5
+  default-language:    Haskell2010
+
+source-repository head
+  type:     git
+  location: https://github.com/NorfairKing/validity