Add IO examples

Author: subev

chapter-29/WhatHappens.hs

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+module WhatHappens where
+
+import Control.Concurrent
+import Debug.Trace
+
+myData :: IO (MVar Int)
+myData = newEmptyMVar
+
+main :: IO ()
+main = do
+  mv <- myData
+  putMVar mv 0
+  mv' <- myData
+  zero <- takeMVar mv'
+  print zero
+
+
+blah :: IO String
+blah = return "blah"
+
+blah' = trace "outer trace" blah
+
+woot :: IO String
+woot = return (trace "inner trace" "woot")
+
+main2 :: IO ()
+main2 = do
+  b <- blah'
+  putStrLn b
+  putStrLn b
+  w <- woot
+  putStrLn w
+  putStrLn w

chapter-29/io-chapter/LICENSE

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+Copyright Author name here (c) 2017
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Author name here nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

chapter-29/io-chapter/README.md

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+# io-chapter

chapter-29/io-chapter/Setup.hs

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+import Distribution.Simple
+main = defaultMain

chapter-29/io-chapter/app/IORefTrans.hs

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+module IORefTrans where
+
+import Control.Monad (replicateM)
+import System.Random (randomRIO)
+
+gimmeShelter :: Bool -> IO [Int]
+gimmeShelter True = replicateM 10 (randomRIO (0, 10))
+gimmeShelter False = pure [0]
+
+

chapter-29/io-chapter/app/Main.hs

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+module Main where
+
+main :: IO ()
+main = undefined

chapter-29/io-chapter/app/NestedIO.hs

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+module NestedIO where
+
+import Data.Time.Calendar
+import Data.Time.Clock
+import System.Random
+
+huehue :: IO (Either (IO Int) (IO ()))
+huehue = do
+  t <- getCurrentTime
+  let (_, _, dayOfMonth) = toGregorian (utctDay t)
+  case even dayOfMonth of
+    True -> return $ Left randomIO
+    False -> return $ Right (putStrLn "no soup for you")

chapter-29/io-chapter/io-chapter.cabal

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+name:                io-chapter
+version:             0.1.0.0
+-- synopsis:
+-- description:
+homepage:            https://github.com/githubuser/io-chapter#readme
+license:             BSD3
+license-file:        LICENSE
+author:              Author name here
+maintainer:          example@example.com
+copyright:           2017 Author name here
+category:            Web
+build-type:          Simple
+extra-source-files:  README.md
+cabal-version:       >=1.10
+
+executable io-chapter-exe
+  hs-source-dirs:      app
+  main-is:             Main.hs
+  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
+  build-depends:       base
+                     , io-chapter
+                     , random
+                     , time
+  default-language:    Haskell2010
+
+source-repository head
+  type:     git
+  location: https://github.com/githubuser/io-chapter