Add remaining haskell book exercises

Haskell-book/26/Embedded/Embedded.cabal

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+-- This file has been generated from package.yaml by hpack version 0.20.0.
+--
+-- see: https://github.com/sol/hpack
+--
+-- hash: 4aaf9c578000b87231817edc542c283c58e2e1562cc290df37e9e8a9628885b0
+
+name:           Embedded
+version:        0.1.0.0
+author:         Eugen Wissner
+maintainer:     belka@caraus.de
+copyright:      2018 Eugen Wissner
+license:        BSD3
+build-type:     Simple
+cabal-version:  >= 1.10
+
+library
+  hs-source-dirs:
+      src
+  build-depends:
+      base >=4.7 && <5
+    , transformers
+  exposed-modules:
+      OuterInner
+  other-modules:
+      Paths_Embedded
+  default-language: Haskell2010
+
+test-suite Embedded-test
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  hs-source-dirs:
+      test
+  ghc-options: -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      Embedded
+    , base >=4.7 && <5
+    , transformers
+  other-modules:
+      Paths_Embedded
+  default-language: Haskell2010

Haskell-book/26/Embedded/Setup.hs

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+import Distribution.Simple
+main = defaultMain

Haskell-book/26/Embedded/package.yaml

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+name:                Embedded
+version:             0.1.0.0
+license:             BSD3
+author:              "Eugen Wissner"
+maintainer:          "belka@caraus.de"
+copyright:           "2018 Eugen Wissner"
+
+dependencies:
+- base >= 4.7 && < 5
+- transformers
+
+library:
+  source-dirs: src
+
+tests:
+  Embedded-test:
+    main:                Spec.hs
+    source-dirs:         test
+    ghc-options:
+    - -threaded
+    - -rtsopts
+    - -with-rtsopts=-N
+    dependencies:
+    - Embedded

Haskell-book/26/Embedded/src/OuterInner.hs

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+module OuterInner where
+
+import Control.Monad.Trans.Except
+import Control.Monad.Trans.Maybe
+import Control.Monad.Trans.Reader
+
+-- We only need to use return once
+-- because it's one big Monad
+embedded :: MaybeT
+            (ExceptT String
+                    (ReaderT () IO))
+            Int
+--embedded = return 1
+embedded = MaybeT . ExceptT . ReaderT $ return . (const (Right (Just 1)))
+
+-- We can sort of peel away the layers one by one:
+maybeUnwrap :: ExceptT String
+               (ReaderT () IO) (Maybe Int)
+maybeUnwrap = runMaybeT embedded
+
+-- Next
+eitherUnwrap :: ReaderT () IO
+                (Either String (Maybe Int))
+eitherUnwrap = runExceptT maybeUnwrap
+
+-- Lastly
+readerUnwrap :: ()
+             -> IO (Either String
+                           (Maybe Int))
+readerUnwrap = runReaderT eitherUnwrap

Haskell-book/26/Embedded/stack.yaml

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+# This file was automatically generated by 'stack init'
+#
+# Some commonly used options have been documented as comments in this file.
+# For advanced use and comprehensive documentation of the format, please see:
+# https://docs.haskellstack.org/en/stable/yaml_configuration/
+
+# Resolver to choose a 'specific' stackage snapshot or a compiler version.
+# A snapshot resolver dictates the compiler version and the set of packages
+# to be used for project dependencies. For example:
+#
+# resolver: lts-3.5
+# resolver: nightly-2015-09-21
+# resolver: ghc-7.10.2
+# resolver: ghcjs-0.1.0_ghc-7.10.2
+# resolver:
+#  name: custom-snapshot
+#  location: "./custom-snapshot.yaml"
+resolver: lts-11.7
+
+# User packages to be built.
+# Various formats can be used as shown in the example below.
+#
+# packages:
+# - some-directory
+# - https://example.com/foo/bar/baz-0.0.2.tar.gz
+# - location:
+#    git: https://github.com/commercialhaskell/stack.git
+#    commit: e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+# - location: https://github.com/commercialhaskell/stack/commit/e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+#   extra-dep: true
+#  subdirs:
+#  - auto-update
+#  - wai
+#
+# A package marked 'extra-dep: true' will only be built if demanded by a
+# non-dependency (i.e. a user package), and its test suites and benchmarks
+# will not be run. This is useful for tweaking upstream packages.
+packages:
+- .
+# Dependency packages to be pulled from upstream that are not in the resolver
+# (e.g., acme-missiles-0.3)
+# extra-deps: []
+
+# Override default flag values for local packages and extra-deps
+# flags: {}
+
+# Extra package databases containing global packages
+# extra-package-dbs: []
+
+# Control whether we use the GHC we find on the path
+# system-ghc: true
+#
+# Require a specific version of stack, using version ranges
+# require-stack-version: -any # Default
+# require-stack-version: ">=1.6"
+#
+# Override the architecture used by stack, especially useful on Windows
+# arch: i386
+# arch: x86_64
+#
+# Extra directories used by stack for building
+# extra-include-dirs: [/path/to/dir]
+# extra-lib-dirs: [/path/to/dir]
+#
+# Allow a newer minor version of GHC than the snapshot specifies
+# compiler-check: newer-minor

Haskell-book/26/Embedded/test/Spec.hs

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+main :: IO ()
+main = putStrLn "Test suite not yet implemented"

Haskell-book/26/Exercises/.gitignore

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+.stack-work/
+Exercises.cabal
+*~

Haskell-book/26/Exercises/Setup.hs

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+import Distribution.Simple
+main = defaultMain

Haskell-book/26/Exercises/app/Main.hs

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+{-# LANGUAGE OverloadedStrings #-}
+
+module Main where
+
+import Control.Monad.IO.Class
+import Control.Monad.Trans.Class
+import Control.Monad.Trans.Reader
+import Data.IORef
+import qualified Data.Map as M
+import Data.Maybe (fromMaybe)
+import Data.Text.Lazy (Text)
+import qualified Data.Text.Lazy as TL
+import System.Environment (getArgs)
+import Web.Scotty.Trans ( ScottyT(..)
+                        , ActionT(..)
+                        , scottyT
+                        , get
+                        , html
+                        , param )
+
+data Config =
+    Config {
+        -- that's one, one click!
+        -- two...two clicks!
+        -- Three BEAUTIFUL clicks! ah ah ahhhh
+        counts :: IORef (M.Map Text Integer)
+      , prefix :: Text
+    }
+
+type Scotty = ScottyT Text (ReaderT Config IO)
+
+bumpBoomp :: Text
+    -> M.Map Text Integer
+    -> (M.Map Text Integer, Integer)
+bumpBoomp k m =
+    let (maybeCount, newMap) = M.insertLookupWithKey (\_ _ oldCount -> oldCount + 1) k 1 m
+    in case maybeCount of
+        Nothing -> (newMap, 1)
+        Just oldCount -> (newMap, oldCount + 1)
+
+app :: Scotty ()
+app =
+    get "/:key" $ do
+        unprefixed <- param "key"
+        prefix <- lift $ asks prefix
+        let key' = mappend prefix unprefixed
+        counts <- lift $ asks counts
+        (newMap, newInteger) <- liftIO $ bumpBoomp key' <$> readIORef counts
+        liftIO $ writeIORef counts newMap
+        html $ mconcat [ "<h1>Success! Count was: "
+                       , TL.pack $ show (newInteger :: Integer)
+                       , "</h1>"
+                       ]
+
+main :: IO ()
+main = do
+    [prefixArg] <- getArgs
+    counter <- newIORef M.empty
+    let config = Config {counts = counter, prefix = TL.pack prefixArg}
+        runR = flip runReaderT config
+    scottyT 3000 runR app

Haskell-book/26/Exercises/package.yaml

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+name:                Exercises
+version:             0.1.0.0
+license:             BSD3
+author:              "Eugen Wissner"
+maintainer:          "belka@caraus.de"
+copyright:           "2018 Eugen Wissner"
+
+dependencies:
+- base >= 4.7 && < 5
+- containers
+- scotty
+- transformers
+- text
+
+library:
+  source-dirs: src
+
+executables:
+  HitCounter:
+    main:        Main.hs
+    source-dirs: app
+    ghc-options:
+    - -threaded
+    - -rtsopts
+    - -with-rtsopts=-N
+
+tests:
+  Exercises-test:
+    main:                Spec.hs
+    source-dirs:         test
+    ghc-options:
+    - -threaded
+    - -rtsopts
+    - -with-rtsopts=-N
+    dependencies:
+    - Exercises
+    - hspec

Haskell-book/26/Exercises/src/Exercises.hs

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+module Exercises where
+
+import Control.Monad.IO.Class (liftIO)
+import Control.Monad.Trans.Class (lift)
+import Control.Monad.Trans.Reader (Reader(..), ReaderT(..), runReader, runReaderT)
+import Control.Monad.Trans.State (StateT(..))
+import Data.Functor.Identity (Identity(..))
+
+-- 1. rDec is a function that should get its argument in the context of
+-- Reader and return a value decremented by one.
+--
+-- Note that “Reader” from transformers is ReaderT of Identity and
+-- that runReader is a convenience function throwing away the
+-- meaningless structure for you. Play with runReaderT if you like.
+rDec :: Num a => Reader a a
+rDec = ReaderT $ dec
+    where dec :: Num a => a -> Identity a
+          dec = return . (flip (-) 1)
+
+-- 2. Once you have an rDec that works, make it and any inner lamb-
+-- das pointfree if that’s not already the case.
+
+
+-- 3. rShow is show, but in Reader.
+rShow :: Show a => Reader a String
+rShow = ReaderT $ toString
+    where toString = return . show
+
+-- 4. Once you have an rShow that works, make it pointfree.
+
+
+-- 5. rPrintAndInc will first print the input with a greeting, then return
+-- the input incremented by one.
+rPrintAndInc :: (Num a, Show a) => ReaderT a IO a
+rPrintAndInc = ReaderT print
+    where print x = do
+            liftIO $ putStrLn $ "Hi: " ++ show x
+            return $ x + 1
+
+-- Prelude> runReaderT rPrintAndInc 1
+-- Hi: 1
+-- 2
+-- Prelude> traverse (runReaderT rPrintAndInc) [1..10]
+-- Hi: 1
+-- Hi: 2
+-- Hi: 3
+-- Hi: 4
+-- Hi: 5
+-- Hi: 6
+-- Hi: 7
+-- Hi: 8
+-- Hi: 9
+-- Hi: 10
+-- [2,3,4,5,6,7,8,9,10,11]
+
+
+-- 6. sPrintIncAccum first prints the input with a greeting, then puts
+-- the incremented input as the new state, and returns the original
+-- input as a String.
+sPrintIncAccum :: (Num a, Show a) => StateT a IO String
+sPrintIncAccum = StateT print
+    where print x = do
+            liftIO $ putStrLn $ "Hi: " ++ show x
+            return $ (show x, x + 1)
+
+-- Prelude> runStateT sPrintIncAccum 10
+-- Hi: 10
+-- ("10",11)
+-- Prelude> mapM (runStateT sPrintIncAccum) [1..5]
+-- Hi: 1
+-- Hi: 2
+-- Hi: 3
+-- Hi: 4
+-- Hi: 5
+-- [("1",2),("2",3),("3",4),("4",5),("5",6)]

Haskell-book/26/Exercises/src/Fix.hs

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+module Fix where
+
+import Control.Monad.IO.Class (liftIO)
+import Control.Monad.Trans.Maybe
+import Control.Monad
+
+isValid :: String -> Bool
+isValid v = '!' `elem` v
+
+maybeExcite :: MaybeT IO String
+maybeExcite = do
+    v <- liftIO getLine
+    guard $ isValid v
+    return v
+
+doExcite :: IO ()
+doExcite = do
+    putStrLn "say something excite!"
+    excite <- runMaybeT maybeExcite
+    case excite of
+      Nothing -> putStrLn "MOAR EXCITE"
+      Just e ->
+          putStrLn
+            ("Good, was very excite: " ++ e)

Haskell-book/26/Exercises/stack.yaml

@@ -0,0 +1,65 @@
+# This file was automatically generated by 'stack init'
+#
+# Some commonly used options have been documented as comments in this file.
+# For advanced use and comprehensive documentation of the format, please see:
+# https://docs.haskellstack.org/en/stable/yaml_configuration/
+
+# Resolver to choose a 'specific' stackage snapshot or a compiler version.
+# A snapshot resolver dictates the compiler version and the set of packages
+# to be used for project dependencies. For example:
+#
+# resolver: lts-3.5
+# resolver: nightly-2015-09-21
+# resolver: ghc-7.10.2
+# resolver: ghcjs-0.1.0_ghc-7.10.2
+#
+# The location of a snapshot can be provided as a file or url. Stack assumes
+# a snapshot provided as a file might change, whereas a url resource does not.
+#
+# resolver: ./custom-snapshot.yaml
+# resolver: https://example.com/snapshots/2018-01-01.yaml
+resolver: lts-11.8
+
+# User packages to be built.
+# Various formats can be used as shown in the example below.
+#
+# packages:
+# - some-directory
+# - https://example.com/foo/bar/baz-0.0.2.tar.gz
+# - location:
+#    git: https://github.com/commercialhaskell/stack.git
+#    commit: e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+# - location: https://github.com/commercialhaskell/stack/commit/e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+#  subdirs:
+#  - auto-update
+#  - wai
+packages:
+- .
+# Dependency packages to be pulled from upstream that are not in the resolver
+# using the same syntax as the packages field.
+# (e.g., acme-missiles-0.3)
+# extra-deps: []
+
+# Override default flag values for local packages and extra-deps
+# flags: {}
+
+# Extra package databases containing global packages
+# extra-package-dbs: []
+
+# Control whether we use the GHC we find on the path
+# system-ghc: true
+#
+# Require a specific version of stack, using version ranges
+# require-stack-version: -any # Default
+# require-stack-version: ">=1.7"
+#
+# Override the architecture used by stack, especially useful on Windows
+# arch: i386
+# arch: x86_64
+#
+# Extra directories used by stack for building
+# extra-include-dirs: [/path/to/dir]
+# extra-lib-dirs: [/path/to/dir]
+#
+# Allow a newer minor version of GHC than the snapshot specifies
+# compiler-check: newer-minor

Haskell-book/26/Exercises/test/Spec.hs

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+import Control.Monad.Trans.Reader
+import Exercises
+import Test.Hspec
+
+main :: IO ()
+main = hspec $ do
+    describe "rDec" $ do
+        it "returns a value decremented by one" $ do
+            runReader rDec 1 `shouldBe` 0
+
+        it "decrements all elements of a list" $ do
+            (fmap (runReader rDec) [1..10]) `shouldBe` [0,1,2,3,4,5,6,7,8,9]
+
+    describe "rShow" $ do
+        it "shows a number" $ do
+            runReader rShow 1 `shouldBe` "1"
+
+        it "shows a list" $ do
+            (fmap (runReader rShow) [1..10]) `shouldBe` ["1","2","3","4","5","6","7","8","9","10"]

Haskell-book/26/MaybeT/.gitignore

@@ -0,0 +1,3 @@
+.stack-work/
+MaybeT.cabal
+*~

Haskell-book/26/MaybeT/Setup.hs

@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain

Haskell-book/26/MaybeT/package.yaml

@@ -0,0 +1,23 @@
+name:                MaybeT
+version:             0.1.0.0
+license:             BSD3
+author:              "Eugen Wissner"
+maintainer:          "belka@caraus.de"
+copyright:           "2018 Eugen Wissner"
+
+dependencies:
+- base >= 4.7 && < 5
+
+library:
+  source-dirs: src
+
+tests:
+  MaybeT-test:
+    main:                Spec.hs
+    source-dirs:         test
+    ghc-options:
+    - -threaded
+    - -rtsopts
+    - -with-rtsopts=-N
+    dependencies:
+    - MaybeT

Haskell-book/26/MaybeT/src/Either.hs

@@ -0,0 +1,56 @@
+module Either where
+
+import Control.Monad (liftM)
+import MonadTrans
+import MonadIO
+
+newtype EitherT e m a =
+    EitherT { runEitherT :: m (Either e a) }
+
+-- 1
+instance Functor m => Functor (EitherT e m) where
+    fmap f (EitherT x) = EitherT $ (fmap . fmap) f x
+
+-- 2
+instance Applicative m => Applicative (EitherT e m) where
+    pure x = EitherT $ pure $ pure x
+
+    (EitherT f) <*> (EitherT a) = EitherT $ (<*>) <$> f <*> a
+
+-- 3
+instance Monad m => Monad (EitherT e m) where
+    return = pure
+
+    (EitherT em) >>= f = EitherT $ do
+        v <- em
+        case v of
+            Left y -> return $ Left y
+            Right y -> runEitherT (f y)
+
+
+-- 4
+-- transformer version of swapEither.
+-- Hint: write swapEither first, then swapEitherT in terms of the former.
+swapEither :: Either e a -> Either a e
+swapEither (Left x) = Right x
+swapEither (Right y) = Left y
+
+swapEitherT :: (Functor m)
+            => EitherT e m a
+            -> EitherT a m e
+swapEitherT (EitherT x) = EitherT $ fmap swapEither x
+
+-- 5. Write the transformer variant of the either catamorphism.
+eitherT :: Monad m
+        => (a -> m c)
+        -> (b -> m c)
+        -> EitherT a m b
+        -> m c
+eitherT f g (EitherT x) = x >>= (either f g)
+
+instance MonadTrans (EitherT e) where
+    lift = EitherT . liftM Right
+
+instance (MonadIO m)
+  => MonadIO (EitherT e m) where
+      liftIO = lift . liftIO

Haskell-book/26/MaybeT/src/Identity.hs

@@ -0,0 +1,43 @@
+module Identity where
+
+import MonadIO
+import MonadTrans
+
+newtype Identity a =
+    Identity { runIdentity :: a }
+    deriving (Eq, Show)
+
+instance Functor Identity where
+    fmap f (Identity a) = Identity (f a)
+
+instance Applicative Identity where
+    pure = Identity
+    (Identity f) <*> (Identity a) = Identity (f a)
+
+newtype IdentityT f a =
+    IdentityT { runIdentityT :: f a }
+    deriving (Eq, Show)
+
+instance (Functor m)
+  => Functor (IdentityT m) where
+      fmap f (IdentityT fa) = IdentityT (fmap f fa)
+
+instance (Applicative m)
+  => Applicative (IdentityT m) where
+      pure x = IdentityT (pure x)
+
+      (IdentityT fab) <*> (IdentityT fa) =
+          IdentityT (fab <*> fa)
+
+instance (Monad m)
+  => Monad (IdentityT m) where
+      return = pure
+
+      (IdentityT ma) >>= f = IdentityT $ ma >>= runIdentityT . f
+
+instance (MonadIO m)
+  => MonadIO (IdentityT m) where
+      liftIO = IdentityT . liftIO
+
+instance MonadTrans IdentityT where
+    lift = IdentityT

Haskell-book/26/MaybeT/src/Maybe.hs

@@ -0,0 +1,40 @@
+module Maybe where
+
+import Control.Monad
+import MonadIO
+import MonadTrans
+
+newtype MaybeT m a =
+    MaybeT { runMaybeT :: m (Maybe a) }
+
+-- compare to the instance for MaybeT
+instance (Functor m)
+      => Functor (MaybeT m) where
+        fmap f (MaybeT ma) =
+            MaybeT $ (fmap . fmap) f ma
+
+instance (Applicative m)
+      => Applicative (MaybeT m) where
+        pure x = MaybeT (pure (pure x))
+
+        (MaybeT fab) <*> (MaybeT mma) = MaybeT $ (<*>) <$> fab <*> mma
+
+instance (Monad m)
+      => Monad (MaybeT m) where
+        return = pure
+
+        -- (>>=) :: MaybeT m a -> (a -> MaybeT m b) -> MaybeT m b
+        (MaybeT ma) >>= f = MaybeT $ do
+            -- ma :: m (Maybe a)
+            -- v :: Maybe a
+            v <- ma
+            case v of
+                Nothing -> return Nothing
+                Just y -> runMaybeT (f y)
+
+instance MonadTrans MaybeT where
+    lift = MaybeT . liftM Just
+
+instance (MonadIO m)
+  => MonadIO (MaybeT m) where
+      liftIO = lift . liftIO

Haskell-book/26/MaybeT/src/MonadIO.hs

@@ -0,0 +1,5 @@
+module MonadIO where
+
+class (Monad m) => MonadIO m where
+    -- | Lift a computation from the 'IO' monad.
+    liftIO :: IO a -> m a

Haskell-book/26/MaybeT/src/MonadTrans.hs

@@ -0,0 +1,7 @@
+module MonadTrans where
+
+class MonadTrans t where
+    -- | Lift a computation from
+    -- the argument monad to
+    -- the constructed monad.
+    lift :: (Monad m) => m a -> t m a

Haskell-book/26/MaybeT/src/Reader.hs

@@ -0,0 +1,35 @@
+module Reader where
+
+import MonadIO
+import MonadTrans
+
+newtype ReaderT r m a =
+    ReaderT { runReaderT :: r -> m a }
+
+instance (Functor m)
+      => Functor (ReaderT r m) where
+    fmap f (ReaderT rma) =
+        ReaderT $ (fmap . fmap) f rma
+
+instance (Applicative m)
+      => Applicative (ReaderT r m) where
+    pure a = ReaderT (pure (pure a))
+
+    (ReaderT fmab) <*> (ReaderT rma) =
+        ReaderT $ (<*>) <$> fmab <*> rma
+
+instance (Monad m)
+      => Monad (ReaderT r m) where
+    return = pure
+
+    (ReaderT rma) >>= f =
+        ReaderT $ \r -> do
+            a <- rma r
+            runReaderT (f a) r
+
+instance MonadTrans (ReaderT r) where
+    lift = ReaderT . const
+
+instance (MonadIO m)
+  => MonadIO (ReaderT r m) where
+      liftIO = lift . liftIO

Haskell-book/26/MaybeT/src/State.hs

@@ -0,0 +1,41 @@
+module State where
+
+import MonadIO
+import MonadTrans
+
+newtype StateT s m a =
+    StateT { runStateT :: s -> m (a, s) }
+
+-- 1
+instance (Functor m)
+      => Functor (StateT s m) where
+    fmap f (StateT m) = StateT $ \s -> fmap first $ m s
+            where first = uncurry (\t1 t2 -> ((f t1), t2))
+            
+-- 2
+-- Links:
+--   http://stackoverflow.com/questions/18673525/is-it-possible-to-implement-applicative-m-applicative-statet-s-m
+--   https://github.com/NICTA/course/issues/134
+instance (Monad m)
+      => Applicative (StateT s m) where
+    pure x = StateT $ (\s -> pure (x, s))
+    StateT g <*> StateT h = StateT $ \s -> keepFirst <$> g s <*> h s
+        where keepFirst (f, s') (x, _) = (f x, s')
+  
+
+-- 3
+instance (Monad m)
+      => Monad (StateT s m) where
+    return = pure
+
+    (StateT sma) >>= f =
+        StateT $ \s -> do
+            a <- sma s
+            runStateT (f $ fst a) s
+
+instance MonadTrans (StateT s) where
+    lift c = StateT $ \s -> c >>= (\x -> return (x, s))
+
+instance (MonadIO m)
+  => MonadIO (StateT s m) where
+      liftIO = lift . liftIO

Haskell-book/26/MaybeT/stack.yaml

@@ -0,0 +1,66 @@
+# This file was automatically generated by 'stack init'
+#
+# Some commonly used options have been documented as comments in this file.
+# For advanced use and comprehensive documentation of the format, please see:
+# https://docs.haskellstack.org/en/stable/yaml_configuration/
+
+# Resolver to choose a 'specific' stackage snapshot or a compiler version.
+# A snapshot resolver dictates the compiler version and the set of packages
+# to be used for project dependencies. For example:
+#
+# resolver: lts-3.5
+# resolver: nightly-2015-09-21
+# resolver: ghc-7.10.2
+# resolver: ghcjs-0.1.0_ghc-7.10.2
+# resolver:
+#  name: custom-snapshot
+#  location: "./custom-snapshot.yaml"
+resolver: lts-11.6
+
+# User packages to be built.
+# Various formats can be used as shown in the example below.
+#
+# packages:
+# - some-directory
+# - https://example.com/foo/bar/baz-0.0.2.tar.gz
+# - location:
+#    git: https://github.com/commercialhaskell/stack.git
+#    commit: e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+# - location: https://github.com/commercialhaskell/stack/commit/e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+#   extra-dep: true
+#  subdirs:
+#  - auto-update
+#  - wai
+#
+# A package marked 'extra-dep: true' will only be built if demanded by a
+# non-dependency (i.e. a user package), and its test suites and benchmarks
+# will not be run. This is useful for tweaking upstream packages.
+packages:
+- .
+# Dependency packages to be pulled from upstream that are not in the resolver
+# (e.g., acme-missiles-0.3)
+# extra-deps: []
+
+# Override default flag values for local packages and extra-deps
+# flags: {}
+
+# Extra package databases containing global packages
+# extra-package-dbs: []
+
+# Control whether we use the GHC we find on the path
+# system-ghc: true
+#
+# Require a specific version of stack, using version ranges
+# require-stack-version: -any # Default
+# require-stack-version: ">=1.6"
+#
+# Override the architecture used by stack, especially useful on Windows
+# arch: i386
+# arch: x86_64
+#
+# Extra directories used by stack for building
+# extra-include-dirs: [/path/to/dir]
+# extra-lib-dirs: [/path/to/dir]
+#
+# Allow a newer minor version of GHC than the snapshot specifies
+# compiler-check: newer-minor

Haskell-book/26/MaybeT/test/Spec.hs

@@ -0,0 +1,2 @@
+main :: IO ()
+main = putStrLn "Test suite not yet implemented"

Haskell-book/26/Morra/.gitignore

@@ -0,0 +1,3 @@
+.stack-work/
+Morra.cabal
+*~

Haskell-book/26/Morra/Setup.hs

@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain

Haskell-book/26/Morra/app/Main.hs

@@ -0,0 +1,69 @@
+module Main where
+
+import Control.Monad
+import Control.Monad.Trans.State
+import System.Random
+import System.Console.ANSI (clearScreen)
+
+type Score = StateT (Integer, Integer) IO (Integer, Integer)
+
+yourTurn :: IO (Integer, Integer)
+yourTurn = do
+    putStrLn "Wie viele Finger zeigen Sie?"
+    shown <- liftM read getLine
+
+    putStrLn "Wie viele Finger wird der Gegner zeigen?"
+    guessed <- liftM read getLine
+
+    clearScreen
+
+    return (shown, guessed)
+
+
+aiTurn :: IO (Integer, Integer)
+aiTurn = do
+    gen1 <- getStdGen
+
+    let (shown, gen2) = randomR (1, 5) gen1
+    putStrLn $ "Der Gegner zeigt: " ++ (show shown)
+
+    let (guessed, gen3) = randomR (1, 5) gen2
+    putStrLn $ "Der Gegner hat " ++ (show guessed) ++ " geraten."
+
+    setStdGen gen3
+    return (shown, guessed)
+
+
+score :: IO (Integer, Integer) -> Score
+score partnerTurn = StateT $ \(s1, s2) -> do
+    you <- yourTurn
+    partner <- partnerTurn
+    let sum = (fst you) + (snd partner)
+
+    let yourScore = if (snd you) == sum then 1 else 0
+    let partnerScore = if (snd partner) == sum then 1 else 0
+    return ((yourScore, partnerScore), (s1 + yourScore, s2 + partnerScore))
+
+
+loopGame :: IO (Integer, Integer)
+         -> (Integer, Integer)
+         -> IO (Either (Integer, Integer) (Integer, Integer))
+loopGame partnerTurn currentScore = do
+    (result, s) <- runStateT (score partnerTurn) currentScore
+    putStrLn $ show $ result
+
+    case s of
+      (16, _) -> return $ Left result
+      (_, 16) -> return $ Right result
+      _       -> loopGame partnerTurn s
+
+
+main :: IO ()
+main = do
+    winner <- loopGame aiTurn (0, 0)
+
+    case winner of
+      Left x ->  putStrLn $ "You've won! Score: " ++ (show x)
+      Right x -> putStrLn $ "You've lost! Score: " ++ (show x)
+
+    return ()

Haskell-book/26/Morra/package.yaml

@@ -0,0 +1,21 @@
+name:                Morra
+version:             0.1.0.0
+license:             BSD3
+author:              "Eugen Wissner"
+maintainer:          "belka@caraus.de"
+copyright:           "2018 Eugen Wissner"
+
+dependencies:
+- base >= 4.7 && < 5
+- random
+- transformers
+- ansi-terminal
+
+executables:
+  morra:
+    main:                Main.hs
+    source-dirs:         app
+    ghc-options:
+    - -threaded
+    - -rtsopts
+    - -with-rtsopts=-N

Haskell-book/26/Morra/stack.yaml

@@ -0,0 +1,65 @@
+# This file was automatically generated by 'stack init'
+#
+# Some commonly used options have been documented as comments in this file.
+# For advanced use and comprehensive documentation of the format, please see:
+# https://docs.haskellstack.org/en/stable/yaml_configuration/
+
+# Resolver to choose a 'specific' stackage snapshot or a compiler version.
+# A snapshot resolver dictates the compiler version and the set of packages
+# to be used for project dependencies. For example:
+#
+# resolver: lts-3.5
+# resolver: nightly-2015-09-21
+# resolver: ghc-7.10.2
+# resolver: ghcjs-0.1.0_ghc-7.10.2
+#
+# The location of a snapshot can be provided as a file or url. Stack assumes
+# a snapshot provided as a file might change, whereas a url resource does not.
+#
+# resolver: ./custom-snapshot.yaml
+# resolver: https://example.com/snapshots/2018-01-01.yaml
+resolver: lts-11.9
+
+# User packages to be built.
+# Various formats can be used as shown in the example below.
+#
+# packages:
+# - some-directory
+# - https://example.com/foo/bar/baz-0.0.2.tar.gz
+# - location:
+#    git: https://github.com/commercialhaskell/stack.git
+#    commit: e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+# - location: https://github.com/commercialhaskell/stack/commit/e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+#  subdirs:
+#  - auto-update
+#  - wai
+packages:
+- .
+# Dependency packages to be pulled from upstream that are not in the resolver
+# using the same syntax as the packages field.
+# (e.g., acme-missiles-0.3)
+# extra-deps: []
+
+# Override default flag values for local packages and extra-deps
+# flags: {}
+
+# Extra package databases containing global packages
+# extra-package-dbs: []
+
+# Control whether we use the GHC we find on the path
+# system-ghc: true
+#
+# Require a specific version of stack, using version ranges
+# require-stack-version: -any # Default
+# require-stack-version: ">=1.7"
+#
+# Override the architecture used by stack, especially useful on Windows
+# arch: i386
+# arch: x86_64
+#
+# Extra directories used by stack for building
+# extra-include-dirs: [/path/to/dir]
+# extra-lib-dirs: [/path/to/dir]
+#
+# Allow a newer minor version of GHC than the snapshot specifies
+# compiler-check: newer-minor