stackbuilders · mrkkrp · Feb 1, 2017 · Jan 22, 2017 · Jan 27, 2017 · Jan 30, 2017
diff --git a/tutorials/haskell/generics/code/LICENSE.md b/tutorials/haskell/generics/code/LICENSE.md
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright © 2017 Stack Builders
+
+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/tutorials/haskell/generics/code/README.md b/tutorials/haskell/generics/code/README.md
@@ -0,0 +1,9 @@
+# Haskel Generics
+
+Code for the above-mentioned tutorial.
+
+## License
+
+Copyright © 2017 Stack Builders
+
+Distributed under MIT.
diff --git a/tutorials/haskell/generics/code/Setup.hs b/tutorials/haskell/generics/code/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/tutorials/haskell/generics/code/generics.cabal b/tutorials/haskell/generics/code/generics.cabal
@@ -0,0 +1,26 @@
+name:                 generics
+version:              0.1.0
+cabal-version:        >= 1.10
+license:              MIT
+license-file:         LICENSE.md
+author:               Mark Karpov <mkarpov@stackbuilders.com>
+maintainer:           Mark Karpov <mkarpov@stackbuilders.com>
+homepage:             https://github.com/stackbuilders/tutorials
+bug-reports:          https://github.com/stackbuilders/tutorials/issues
+category:             Generics
+synopsis:             Code for the Stack Builders Generics tutorial
+build-type:           Simple
+description:          Code for the Stack Builders Generics tutorial.
+extra-doc-files:      CHANGELOG.md
+                    , README.md
+
+source-repository head
+  type:               git
+  location:           https://github.com/stackbuilders/tutorials.git
+
+library
+  hs-source-dirs:     src
+  build-depends:      base             >= 4.7 && < 5.0
+  exposed-modules:    GenericsTutorial
+  ghc-options:        -O2 -Wall
+  default-language:   Haskell2010
diff --git a/tutorials/haskell/generics/code/src/GenericsTutorial.hs b/tutorials/haskell/generics/code/src/GenericsTutorial.hs
@@ -0,0 +1,54 @@
+{-# LANGUAGE DefaultSignatures #-}
+{-# LANGUAGE DeriveGeneric     #-}
+{-# LANGUAGE FlexibleContexts  #-}
+{-# LANGUAGE TypeFamilies      #-}
+{-# LANGUAGE TypeOperators     #-}
+
+module GenericsTutorial
+  ( CountFields (..) )
+where
+
+import GHC.Generics
+import Numeric.Natural
+import Prelude
+
+class CountFields a where
+  -- | Return number of constructor fields for a value.
+  countFields :: a -> Natural
+  default countFields :: (Generic a, CountFields1 (Rep a)) => a -> Natural
+  countFields = defaultCountFields
+
+defaultCountFields :: (Generic a, CountFields1 (Rep a)) => a -> Natural
+defaultCountFields = countFields1 . from
+
+class CountFields1 f where
+  countFields1 :: f p -> Natural
+
+instance CountFields1 V1 where
+  countFields1 _ = 0
+
+instance CountFields1 U1 where
+  countFields1 _ = 0
+
+instance CountFields1 (K1 i c) where
+  countFields1 _ = 1
+
+instance CountFields1 f => CountFields1 (M1 i c f) where
+  countFields1 (M1 x) = countFields1 x
+
+instance (CountFields1 a, CountFields1 b) => CountFields1 (a :+: b) where
+  countFields1 (L1 x) = countFields1 x
+  countFields1 (R1 x) = countFields1 x
+
+instance (CountFields1 a, CountFields1 b) => CountFields1 (a :*: b) where
+  countFields1 (a :*: b) = countFields1 a + countFields1 b
+
+----------------------------------------------------------------------------
+-- Tests
+
+instance CountFields (Maybe a)
+
+data Foo = Foo Int Int Int | Bar Bool
+  deriving (Show, Generic)
+
+instance CountFields Foo
diff --git a/tutorials/haskell/generics/code/stack.yaml b/tutorials/haskell/generics/code/stack.yaml
@@ -0,0 +1,3 @@
+resolver: lts-7.16
+packages:
+- '.'