diff --git a/.travis.yml b/.travis.yml
new file mode 100644
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,150 @@
+# This is the complex Travis configuration, which is intended for use
+# on open source libraries which need compatibility across multiple GHC
+# versions, must work with cabal-install, and should be
+# cross-platform. For more information and other options, see:
+#
+# https://docs.haskellstack.org/en/stable/travis_ci/
+#
+# Copy these contents into the root directory of your Github project in a file
+# named .travis.yml
+
+# Use new container infrastructure to enable caching
+sudo: false
+
+# Do not choose a language; we provide our own build tools.
+language: generic
+
+# Caching so the next build will be fast too.
+cache:
+  directories:
+  - $HOME/.ghc
+  - $HOME/.cabal
+  - $HOME/.stack
+  - $TRAVIS_BUILD_DIR/.stack-work
+
+# The different configurations we want to test. We have BUILD=cabal which uses
+# cabal-install, and BUILD=stack which uses Stack. More documentation on each
+# of those below.
+#
+# We set the compiler values here to tell Travis to use a different
+# cache file per set of arguments.
+#
+# If you need to have different apt packages for each combination in the
+# matrix, you can use a line such as:
+#     addons: {apt: {packages: [libfcgi-dev,libgmp-dev]}}
+matrix:
+  include:
+  - env: BUILD=cabal GHCVER=8.2.2 CABALVER=2.0 HAPPYVER=1.19.5 ALEXVER=3.1.7
+    compiler: ": #GHC 8.2.2"
+    addons: {apt: {packages: [cabal-install-2.0,ghc-8.2.2,happy-1.19.5,alex-3.1.7], sources: [hvr-ghc]}}
+  - env: BUILD=cabal GHCVER=8.4.3 CABALVER=2.2 HAPPYVER=1.19.5 ALEXVER=3.1.7
+    compiler: ": #GHC 8.4.3"
+    addons: {apt: {packages: [cabal-install-2.2,ghc-8.4.3,happy-1.19.5,alex-3.1.7], sources: [hvr-ghc]}}
+
+  # Build with the newest GHC and cabal-install. This is an accepted failure,
+  # see below.
+  - env: BUILD=cabal GHCVER=head  CABALVER=head HAPPYVER=1.19.5 ALEXVER=3.1.7
+    compiler: ": #GHC HEAD"
+    addons: {apt: {packages: [cabal-install-head,ghc-head,happy-1.19.5,alex-3.1.7], sources: [hvr-ghc]}}
+
+  # The Stack builds. We can pass in arbitrary Stack arguments via the ARGS
+  # variable, such as using --stack-yaml to point to a different file.
+  - env: BUILD=stack ARGS=""
+    compiler: ": #stack default"
+    addons: {apt: {packages: [libgmp-dev]}}
+
+  # Build on macOS in addition to Linux
+  - env: BUILD=stack ARGS=""
+    compiler: ": #stack default osx"
+    os: osx
+
+  allow_failures:
+  - env: BUILD=cabal GHCVER=head  CABALVER=head HAPPYVER=1.19.5 ALEXVER=3.1.7
+
+before_install:
+# Using compiler above sets CC to an invalid value, so unset it
+- unset CC
+
+# We want to always allow newer versions of packages when building on GHC HEAD
+- CABALARGS=""
+- if [ "x$GHCVER" = "xhead" ]; then CABALARGS=--allow-newer; fi
+
+# Download and unpack the stack executable
+- export PATH=/opt/ghc/$GHCVER/bin:/opt/cabal/$CABALVER/bin:$HOME/.local/bin:/opt/alex/$ALEXVER/bin:/opt/happy/$HAPPYVER/bin:$HOME/.cabal/bin:$PATH
+- mkdir -p ~/.local/bin
+- |
+  if [ `uname` = "Darwin" ]
+  then
+    travis_retry curl --insecure -L https://get.haskellstack.org/stable/osx-x86_64.tar.gz | tar xz --strip-components=1 --include '*/stack' -C ~/.local/bin
+  else
+    travis_retry curl -L https://get.haskellstack.org/stable/linux-x86_64.tar.gz | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
+  fi
+
+  # Use the more reliable S3 mirror of Hackage
+  mkdir -p $HOME/.cabal
+  echo 'remote-repo: hackage.haskell.org:http://hackage.fpcomplete.com/' > $HOME/.cabal/config
+  echo 'remote-repo-cache: $HOME/.cabal/packages' >> $HOME/.cabal/config
+
+
+install:
+- echo "$(ghc --version) [$(ghc --print-project-git-commit-id 2> /dev/null || echo '?')]"
+- if [ -f configure.ac ]; then autoreconf -i; fi
+- |
+  set -ex
+  case "$BUILD" in
+    stack)
+      # Add in extra-deps for older snapshots, as necessary
+      stack --no-terminal --install-ghc $ARGS test --bench --dry-run || ( \
+        stack --no-terminal $ARGS build cabal-install && \
+        stack --no-terminal $ARGS solver --update-config)
+
+      # Build the dependencies
+      stack --no-terminal --install-ghc $ARGS test --bench --only-dependencies
+      ;;
+    cabal)
+      cabal --version
+      travis_retry cabal update
+
+      # Get the list of packages from the stack.yaml file. Note that
+      # this will also implicitly run hpack as necessary to generate
+      # the .cabal files needed by cabal-install.
+      PACKAGES=$(stack --install-ghc query locals | grep '^ *path' | sed 's@^ *path:@@')
+
+      cabal install --only-dependencies --enable-tests --enable-benchmarks --force-reinstalls --ghc-options=-O0 --reorder-goals --max-backjumps=-1 $CABALARGS $PACKAGES
+      ;;
+  esac
+  set +ex
+
+script:
+- |
+  set -ex
+  case "$BUILD" in
+    stack)
+      stack --no-terminal $ARGS test --bench --no-run-benchmarks --haddock --no-haddock-deps
+      ;;
+    cabal)
+      cabal install --enable-tests --enable-benchmarks --force-reinstalls --ghc-options=-O0 --reorder-goals --max-backjumps=-1 $CABALARGS $PACKAGES
+
+      ORIGDIR=$(pwd)
+      for dir in $PACKAGES
+      do
+        cd $dir
+        cabal check || [ "$CABALVER" == "1.16" ]
+        cabal sdist
+        PKGVER=$(cabal info . | awk '{print $2;exit}')
+        SRC_TGZ=$PKGVER.tar.gz
+        cd dist
+        tar zxfv "$SRC_TGZ"
+        cd "$PKGVER"
+        cabal configure --enable-tests --ghc-options -O0
+        cabal build
+        if [ "$CABALVER" = "1.16" ] || [ "$CABALVER" = "1.18" ]; then
+          cabal test
+        else
+          cabal test --show-details=streaming --log=/dev/stdout
+        fi
+        cd $ORIGDIR
+      done
+      ;;
+  esac
+  set +ex
diff --git a/appveyor.yml b/appveyor.yml
new file mode 100644
--- /dev/null
+++ b/appveyor.yml
@@ -0,0 +1,19 @@
+build: off
+
+before_test:
+# http://help.appveyor.com/discussions/problems/6312-curl-command-not-found
+- set PATH=C:\Program Files\Git\mingw64\bin;%PATH%
+
+- curl -sS -ostack.zip -L --insecure http://www.stackage.org/stack/windows-i386
+- 7z x stack.zip stack.exe
+
+clone_folder: "c:\\stack"
+environment:
+  global:
+    STACK_ROOT: "c:\\sr"
+
+test_script:
+- stack setup > nul
+# The ugly echo "" hack is to avoid complaints about 0 being an invalid file
+# descriptor
+- echo "" | stack --no-terminal test
diff --git a/dicegame.hs b/dicegame.hs
new file mode 100644
--- /dev/null
+++ b/dicegame.hs
@@ -0,0 +1,35 @@
+import Control.Monad (replicateM)
+import Control.Monad.RWS
+import System.Random
+
+type Dice = Int
+
+type DiceGame = RWS (Int, Int) [Dice] StdGen
+
+dice' :: DiceGame Dice
+dice' = do
+  bs <- ask
+  g <- get
+  let (r, g') = randomR bs g
+  put g'
+  tell [r]
+  pure r
+
+dice :: DiceGame Dice
+dice = do
+  bs <- ask
+  r <- state (randomR bs)
+  tell [r]
+  pure r
+
+doubleDice :: DiceGame (Dice, Dice)
+doubleDice = (,) <$> dice <*> dice
+
+dices :: Int -> DiceGame [Dice]
+dices n = replicateM n dice 
+
+diceGame :: DiceGame (Dice, Dice)
+diceGame = dice >> dices 5 >> replicateM 2 (dices 3)
+                >> dices 10 >> doubleDice
+
+main = newStdGen >>= print . evalRWS diceGame (1, 6)
diff --git a/filecount.hs b/filecount.hs
new file mode 100644
--- /dev/null
+++ b/filecount.hs
@@ -0,0 +1,25 @@
+import Data.Foldable (traverse_)
+import System.Environment (getArgs)
+import System.Directory.Extra
+import Control.Monad.Extra (whenM, ifM, zipWithM)
+import Data.IORef (newIORef, modifyIORef', readIORef)
+
+fileCount :: FilePath -> IO Int
+fileCount fp = do
+   cnt <- newIORef 0
+   whenM (doesDirectoryExist fp) $ go cnt fp 
+   readIORef cnt
+ where
+   go cnt fp = listContents fp >>= traverse_ (processEntry cnt)
+   processEntry cnt fp = ifM (doesDirectoryExist fp) (go cnt fp) (inc cnt)
+   inc cnt = modifyIORef' cnt (+ 1)
+
+fileCount' :: FilePath -> IO Int
+fileCount' fp = length <$> listFilesRecursive fp
+
+main = do
+   args <- getArgs
+   xs <- traverse fileCount args
+   zipWithM printEntry args xs
+ where
+   printEntry fp n = putStrLn (show n ++ "\t" ++ fp)
diff --git a/gcd.hs b/gcd.hs
new file mode 100644
--- /dev/null
+++ b/gcd.hs
@@ -0,0 +1,21 @@
+import Control.Monad.Writer
+
+gcd' :: Integer -> Integer -> Integer
+gcd' a 0 = a
+gcd' a b = gcd b (a `mod` b)
+
+gcd_countSteps :: Integer -> Integer -> Writer (Sum Int) Integer
+gcd_countSteps a 0 = tell (Sum 1) >> pure a
+gcd_countSteps a b = tell (Sum 1) >> gcd_countSteps b (a `mod` b)
+
+gcd_logSteps :: Integer -> Integer -> Writer [(Integer, Integer)] Integer
+gcd_logSteps a 0 = tell [(a,0)] >> pure a
+gcd_logSteps a b = tell [(a,b)] >> gcd_logSteps b (a `mod` b)
+
+gcd_countSteps' a b = mapWriter mapper (gcd_logSteps a b)
+  where
+    mapper (a, w) = (a, Sum $ length w)
+
+gcd_countSteps'' = (mapWriter (Sum . length <$>) .) . gcd_logSteps
+
+main = print "OK"
diff --git a/genSQL.hs b/genSQL.hs
new file mode 100644
--- /dev/null
+++ b/genSQL.hs
@@ -0,0 +1,35 @@
+{-# LANGUAGE OverloadedStrings, ViewPatterns #-}
+
+import Data.Foldable
+import Control.Monad.Writer
+import qualified Data.Text as T
+import qualified Data.Text.IO as TIO
+import Data.Monoid
+
+data ErrorMsg = WrongFormat
+                   Int
+                   T.Text
+  deriving Show
+
+type SQL = T.Text
+
+genInsert s1 s2 = "INSERT INTO items VALUES ('" <> s1 <> "','" <> s2 <> "');\n"
+
+processOneLine :: (Int, T.Text) -> Writer [ErrorMsg] SQL 
+processOneLine (i, T.splitOn ":" -> [s1, s2]) = pure $ genInsert s1 s2
+processOneLine (i, s) = writer (T.empty, [WrongFormat i s])
+
+genSQL :: T.Text -> Writer [ErrorMsg] SQL
+genSQL t = T.concat <$> traverse processOneLine (zip [1..] $ T.lines t)
+
+
+testData = "Pen:Bob\nGlass:Mary:10\nPencil:Alice\nBook:Bob\nBottle"
+
+testGenSQL = do
+  let (sql, errors) = runWriter (genSQL testData) 
+  TIO.putStrLn "SQL:"
+  TIO.putStr sql
+  TIO.putStrLn "Errors:"
+  traverse_ print errors
+
+main = testGenSQL
diff --git a/hid-examples.cabal b/hid-examples.cabal
--- a/hid-examples.cabal
+++ b/hid-examples.cabal
@@ -1,89 +1,204 @@
-name:                hid-examples
-version:             0.1.0.0
-synopsis:            Examples to accompany the book "Haskell in Depth"
-description:
-        This package provides source code examples which accompany the book
-        "Haskell in Depth" by Vitaly Bragilevsky (Manning Publications 2019).
-        You may want to get this package via @cabal get hid-examples@
-        and explore its content.
+cabal-version: >= 1.10
 
-license:             BSD3
-license-file:        LICENSE
-author:              Vitaly Bragilevsky
-maintainer:          Vitaly Bragilevsky <vit.bragilevsky@gmail.com>
-copyright:           (c) Vitaly Bragilevsky 2018
-category:            Sample Code
-build-type:          Simple
-extra-source-files:  ChangeLog.md
-cabal-version:       >=1.10
+-- This file has been generated from package.yaml by hpack version 0.29.7.
+--
+-- see: https://github.com/sol/hpack
+--
+-- hash: 6d9bc7f35a54450595b8cfc3a4fe434408d4bb09fdf34222dfa11b29c8a6861b
 
-bug-reports:         https://github.com/bravit/hid-examples/issues
-homepage:            https://github.com/bravit/hid-examples/
+name:           hid-examples
+version:        0.2
+synopsis:       Examples to accompany the book "Haskell in Depth"
+description:    This package provides source code examples which accompany the book "Haskell in Depth" by Vitaly Bragilevsky (Manning Publications 2019). You may want to get this package via @cabal get hid-examples@ and explore its content.
+category:       Sample Code
+homepage:       https://github.com/bravit/hid-examples#readme
+bug-reports:    https://github.com/bravit/hid-examples/issues
+author:         Vitaly Bragilevsky
+maintainer:     Vitaly Bragilevsky <vit.bragilevsky@gmail.com>
+license:        BSD3
+license-file:   LICENSE
+build-type:     Simple
+extra-source-files:
+    .travis.yml
+    appveyor.yml
+    ChangeLog.md
+    LICENSE
+    package.yaml
+    README.md
+    stack.yaml
+data-files:
+    data/quotes.csv
+    texts/Dracula.srt
+    texts/forsyte.txt
+    texts/hamlet.txt
+    texts/phrase.txt
+    texts/rune-poem.txt
 
-extra-source-files:    ChangeLog.md
-                       LICENSE
-                       README.md
-                       stack.yaml
+source-repository head
+  type: git
+  location: https://github.com/bravit/hid-examples
 
-data-files:            data/quotes.csv
-                       texts/Dracula.srt
-                       texts/*.txt
+executable dicegame
+  main-is: dicegame.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+    , mtl >=2.0 && <2.3
+    , random >=1.0 && <1.2
+  default-language: Haskell2010
 
-source-repository head
-    type:     git
-    location: https://github.com/bravit/hid-examples.git
+executable filecount
+  main-is: filecount.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+    , extra >=1.5 && <1.7
+  default-language: Haskell2010
 
--- -----------------------------------------------------------------------------
--- Chapter 2
+executable gcd
+  main-is: gcd.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+    , mtl >=2.0 && <2.3
+  default-language: Haskell2010
 
-executable locator
-  main-is:             locator.hs
-  build-depends:       base >=4.10 && <4.12
-  default-language:    Haskell2010
+executable genSQL
+  main-is: genSQL.hs
+  other-modules:
+      Paths_hid_examples
+  other-extensions: OverloadedStrings ViewPatterns
+  build-depends:
+      base >=4.10 && <4.12
+    , mtl >=2.0 && <2.3
+    , text >=1.2 && <1.3
+  default-language: Haskell2010
 
-executable vocab1
-  main-is:             vocab1.hs
-  build-depends:       base >=4.10 && <4.12
-                     , text >=1.2 && <1.3
-  default-language:    Haskell2010
+executable ioref
+  main-is: ioref.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+  default-language: Haskell2010
 
-executable vocab2
-  main-is:             vocab2.hs
-  build-depends:       base >=4.10 && <4.12
-                     , text >=1.2 && <1.3
-  default-language:    Haskell2010
+executable locator
+  main-is: locator.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+  default-language: Haskell2010
 
-executable vocab3
-  main-is:             vocab3.hs
-  build-depends:       base >=4.10 && <4.12
-                     , text >=1.2 && <1.3
-  default-language:    Haskell2010
+executable maybe
+  main-is: maybe.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+    , safe >=0.3 && <0.4
+  default-language: Haskell2010
 
+executable reader
+  main-is: reader.hs
+  other-modules:
+      Paths_hid_examples
+  other-extensions: NamedFieldPuns
+  build-depends:
+      base >=4.10 && <4.12
+    , mtl >=2.0 && <2.3
+  default-language: Haskell2010
+
 executable showexpr
-  main-is:             showexpr.hs
-  build-depends:       base >=4.10 && <4.12
-                     , hint >=0.7 && <0.9
-  default-language:    Haskell2010
+  main-is: showexpr.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+    , hint >=0.7 && <0.9
+  default-language: Haskell2010
 
--- -----------------------------------------------------------------------------
--- Chapter 3
+executable shunting-yard
+  main-is: shunting-yard.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+    , mtl >=2.0 && <2.3
+  default-language: Haskell2010
 
 executable stockquotes
-  hs-source-dirs:      stockquotes
-  main-is:             Main.hs
-  other-modules:       BoundedEnum QuoteData Statistics StatReport
-                       Charts HtmlReport Params 
-  other-extensions:    RecordWildCards OverloadedStrings FlexibleInstances
-                       DeriveGeneric DeriveAnyClass
-  build-depends:       base >=4.10 && <4.11
-                     , bytestring >=0.10 && <0.11
-                     , blaze-html >=0.9 && <0.10
-                     , optparse-applicative >=0.14 && <0.15
-                     , time >=1.8 && <1.9
-                     , text >=1.2 && <1.3
-                     , fmt >=0.5 && <0.7
-                     , safe >=0.3 && <0.4
-                     , Chart >=1.8 && <1.9
-                     , Chart-diagrams >=1.8 && <1.9
-                     , cassava >=0.5 && <0.6
-  default-language:    Haskell2010
+  main-is: Main.hs
+  other-modules:
+      BoundedEnum
+      Charts
+      HtmlReport
+      Params
+      QuoteData
+      Statistics
+      StatReport
+      Paths_hid_examples
+  hs-source-dirs:
+      stockquotes
+  other-extensions: RecordWildCards OverloadedStrings FlexibleInstances DeriveGeneric DeriveAnyClass
+  build-depends:
+      Chart >=1.8 && <1.10
+    , Chart-diagrams >=1.8 && <1.10
+    , base >=4.10 && <4.12
+    , blaze-html >=0.9 && <0.10
+    , bytestring >=0.10 && <0.11
+    , cassava >=0.5 && <0.6
+    , fmt >=0.5 && <0.7
+    , optparse-applicative >=0.14 && <0.15
+    , safe >=0.3 && <0.4
+    , text >=1.2 && <1.3
+    , time >=1.8 && <1.10
+  default-language: Haskell2010
+
+executable stref
+  main-is: stref.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+  default-language: Haskell2010
+
+executable vocab1
+  main-is: vocab1.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+    , text >=1.2 && <1.3
+  default-language: Haskell2010
+
+executable vocab2
+  main-is: vocab2.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+    , text >=1.2 && <1.3
+  default-language: Haskell2010
+
+executable vocab3
+  main-is: vocab3.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+    , text >=1.2 && <1.3
+  default-language: Haskell2010
+
+executable weapons
+  main-is: weapons.hs
+  other-modules:
+      Paths_hid_examples
+  build-depends:
+      base >=4.10 && <4.12
+    , mtl >=2.0 && <2.3
+    , random >=1.0 && <1.2
+  default-language: Haskell2010
diff --git a/ioref.hs b/ioref.hs
new file mode 100644
--- /dev/null
+++ b/ioref.hs
@@ -0,0 +1,21 @@
+import Data.IORef
+import Control.Monad
+
+sumNumbers :: IO Int
+sumNumbers = do
+   s <- newIORef 0
+   go s
+   readIORef s
+ where
+   go s = do
+     putStr "Enter next integer number (empty line to finish): "
+     n <- getLine
+     when (not $ null n) $ do
+       let num = read n
+       modifyIORef' s (+ num)
+       go s
+
+main = do
+  s <- sumNumbers
+  putStr "Your sum is: "
+  print s
diff --git a/maybe.hs b/maybe.hs
new file mode 100644
--- /dev/null
+++ b/maybe.hs
@@ -0,0 +1,27 @@
+import Safe
+
+type Name = String
+type Phone = String
+type Location = String
+type PhoneNumbers = [(Name, Phone)]
+type Locations = [(Phone, Location)]
+
+locByName :: PhoneNumbers -> Locations -> Name -> Maybe Location
+locByName pnumbers locs name = lookup name pnumbers >>= flip lookup locs
+
+locByName' :: PhoneNumbers -> Locations -> Name -> Maybe Location
+locByName' pnumbers locs name = case lookup name pnumbers of
+                                   Just number -> lookup number locs
+                                   Nothing -> Nothing
+
+doubleStrNumber :: (Num a, Read a) => String -> Maybe a
+doubleStrNumber s = (*2) <$> readMay s
+
+
+plusStrNumbers :: (Num a, Read a) => String -> String -> Maybe a
+plusStrNumbers s1 s2 = (+) <$> readMay s1 <*> readMay s2
+
+main = do
+  print $ doubleStrNumber "21"
+  print $ plusStrNumbers "10" "xx"
+  
diff --git a/package.yaml b/package.yaml
new file mode 100644
--- /dev/null
+++ b/package.yaml
@@ -0,0 +1,111 @@
+name: hid-examples
+version: 0.2
+synopsis: Examples to accompany the book "Haskell in Depth"
+description:
+        This package provides source code examples which accompany the book
+        "Haskell in Depth" by Vitaly Bragilevsky (Manning Publications 2019).
+        You may want to get this package via @cabal get hid-examples@
+        and explore its content.
+
+category:            Sample Code
+license:             BSD3
+author: Vitaly Bragilevsky
+maintainer: Vitaly Bragilevsky <vit.bragilevsky@gmail.com>
+github: bravit/hid-examples
+extra-source-files:
+    - ChangeLog.md
+    - LICENSE
+    - README.md
+    - stack.yaml
+    - .travis.yml
+    - appveyor.yml
+    - package.yaml
+
+data-files:
+    - data/*.*
+    - texts/*.*
+
+dependencies: base >=4.10 && <4.12
+
+executables:
+    # Chapter 2
+    locator:
+        main: locator.hs
+    vocab1:
+        main: vocab1.hs
+        dependencies: text >=1.2 && <1.3
+    vocab2:
+        main: vocab2.hs
+        dependencies: text >=1.2 && <1.3
+    vocab3:
+        main: vocab3.hs
+        dependencies: text >=1.2 && <1.3
+    showexpr:
+        main: showexpr.hs
+        dependencies: hint >=0.7 && <0.9
+    # Chapter 3
+    stockquotes:
+        source-dirs: stockquotes
+        main: Main.hs
+        other-extensions:
+          - RecordWildCards
+          - OverloadedStrings
+          - FlexibleInstances
+          - DeriveGeneric
+          - DeriveAnyClass
+        dependencies:
+          - bytestring >=0.10 && <0.11
+          - blaze-html >=0.9 && <0.10
+          - optparse-applicative >=0.14 && <0.15
+          - time >=1.8 && <1.10
+          - text >=1.2 && <1.3
+          - fmt >=0.5 && <0.7
+          - safe >=0.3 && <0.4
+          - Chart >=1.8 && <1.10
+          - Chart-diagrams >=1.8 && <1.10
+          - cassava >=0.5 && <0.6
+    # Chapter 5
+    maybe:
+        main: maybe.hs
+        dependencies:
+          - safe >=0.3 && <0.4
+    reader:
+        main: reader.hs
+        other-extensions:
+          - NamedFieldPuns
+        dependencies:
+          - mtl >=2.0 && <2.3
+    genSQL:
+        main: genSQL.hs
+        other-extensions:
+          - OverloadedStrings
+          - ViewPatterns
+        dependencies:
+          - text >=1.2 && <1.3
+          - mtl >=2.0 && <2.3
+    gcd:
+        main: gcd.hs
+        dependencies:
+          - mtl >=2.0 && <2.3
+    weapons:
+        main: weapons.hs
+        dependencies:
+          - mtl >=2.0 && <2.3
+          - random >=1.0 && <1.2
+    shunting-yard:
+        main: shunting-yard.hs
+        dependencies:
+          - mtl >=2.0 && <2.3
+    dicegame:
+        main: dicegame.hs
+        dependencies:
+          - mtl >=2.0 && <2.3
+          - random >=1.0 && <1.2
+    ioref:
+        main: ioref.hs
+    filecount:
+        main: filecount.hs
+        dependencies:
+          - extra >=1.5 && <1.7
+    stref:
+        main: stref.hs
diff --git a/reader.hs b/reader.hs
new file mode 100644
--- /dev/null
+++ b/reader.hs
@@ -0,0 +1,38 @@
+{-# LANGUAGE NamedFieldPuns #-}
+import Control.Monad.Reader
+
+data Config = Config {
+    flag1 :: Bool,
+    flag2 :: Bool
+    -- ...
+  }
+
+type ConfigM = Reader Config
+
+main = do 
+  let c = Config True False
+  pure $ runReader work c
+  print "OK"
+
+work :: ConfigM ()
+work = do
+  -- ...
+  f1
+  -- ...
+
+f1 :: ConfigM ()
+f1 = do
+  -- ...
+  f11
+  -- ...
+
+f11 :: ConfigM ()
+f11 = do
+  -- ...
+  c <- ask
+  -- ...
+  pure ()
+
+nc = \c @ Config {flag1} -> c {flag1 = not flag1}
+
+nc2 = \c -> c {flag1 = False}
diff --git a/shunting-yard.hs b/shunting-yard.hs
new file mode 100644
--- /dev/null
+++ b/shunting-yard.hs
@@ -0,0 +1,177 @@
+import Data.Char
+import Data.List
+import Data.Foldable
+import Control.Monad.State
+
+-- Implementation of the Shunting-yard algorithm
+
+data Expr a = Lit a | Add (Expr a) (Expr a) | Mult (Expr a) (Expr a)
+
+type Token = String
+type Stack = [Token]
+type Output = [Expr Integer]
+type MyState = (Stack, Output)
+
+push :: Token -> State MyState ()
+push t = modify (\(s, es) -> (t : s, es))
+
+pop :: State MyState Token
+pop = do
+  (t : s, es) <- get -- let it crash on empty stack
+  put (s, es)
+  pure t
+
+pop_ :: State MyState ()  -- let it crash on empty stack
+pop_ = modify (\(s, es) -> (tail s, es))
+
+top :: State MyState Token
+top = gets (head . fst) -- let it crash on empty stack
+
+isEmpty :: State MyState Bool
+isEmpty = null <$> gets fst
+
+notEmpty :: State MyState Bool
+notEmpty = not <$> isEmpty
+
+output :: Token -> State MyState ()
+output t = modify (builder t <$>)
+  where 
+    builder "+" (e1 : e2 : es) = Add e1 e2 : es
+    builder "*" (e1 : e2 : es) = Mult e1 e2 : es
+    builder n es = Lit (read n) : es -- let it crash on not a number
+
+whileNotEmptyAnd :: (Token -> Bool) -> State MyState () -> State MyState ()
+whileNotEmptyAnd pred m = go
+  where
+    go = do
+      b1 <- notEmpty
+      when b1 $ do
+        b2 <- pred <$> top
+        when b2 (m >> go)
+
+isOp "+" = True
+isOp "*" = True
+isOp _ = False
+
+precedence "+" = 1
+precedence "*" = 2
+precedence _ = 0
+
+t1 `precGTE` t2 = precedence t1 >= precedence t2 
+
+convertToExpr :: String -> Expr Integer
+convertToExpr str = head $ snd $ execState convert ([], [])
+  where
+    convert = traverse_ processToken (reverse $ tokenize str) >> transferRest
+
+    processToken ")" = push ")"
+    processToken "(" = transferWhile (/= ")") >> pop_
+    processToken t
+      | isOp t = transferWhile (`precGTE` t) >> push t
+      | otherwise = output t -- number
+
+    transfer = pop >>= output
+    transferWhile pred = whileNotEmptyAnd pred transfer
+    transferRest = transferWhile (const True)
+    
+    tokenize = groupBy (\a b -> isDigit a && isDigit b)
+               . filter (not . isSpace)
+
+{-
+
+https://en.wikipedia.org/wiki/Shunting-yard_algorithm
+
+* stack
+* output
+* reading tokens in reversed order
+
+while there are tokens to be read:
+  read a token.
+  if the token is a right bracket (i.e. ")"), then:
+    push it onto the stack.
+  if the token is a left bracket (i.e. "("), then:
+    while the operator at the top of the stack is not a right bracket:
+      pop the operator from the stack onto the output.
+    pop the right bracket from the stack.
+    /* if the stack runs out without finding a right bracket,
+       then there are mismatched parentheses. */
+  if the token is an operator, then:
+    while ((there is an operator at the top of the stack
+                        with equal or greater precedence)
+           and (the operator at the top of the stack
+                is not a left bracket):
+       pop operators from the stack onto the output.
+    push it onto the stack.
+  if the token is a number, then:
+    push it to the output.
+
+if there are no more tokens to read:
+  while there are still operator tokens on the stack:
+    /* if the operator token on the top of the stack is a bracket,
+       then there are mismatched parentheses. */
+    pop the operator from the operator stack onto the output.
+exit.
+
+-}
+
+-- Printing `Expr a` values
+
+instance Show a => Show (Expr a) where
+  showsPrec _ (Lit a)  = shows a
+  showsPrec p (Add e1 e2) = showParen (p > precAdd)
+                            $ showsPrec precAdd e1
+                              . showString "+" 
+                              . showsPrec precAdd e2
+    where precAdd = 5
+  showsPrec p (Mult e1 e2) = showParen (p > precMult)
+                             $ showsPrec (precMult) e1
+                               . showString "*"
+                               . showsPrec (precMult) e2
+    where precMult = 6
+
+-- Evaluating expressions
+
+myeval :: Num a => Expr a -> a
+myeval (Lit e) = e
+myeval (Add e1 e2) = myeval e1 + myeval e2
+myeval (Mult e1 e2) = myeval e1 * myeval e2
+
+-- Testing
+
+strs = ["42", "12 + 13", "(2+3*3)*5", "1+(1+2)*(2+2*(1+2))+1+3*2",
+        "13+2+12+2+1+2+13+2", "1*2*132*22*1*22*0*2", "10*(1+2)*2*(2+1*2)+1+3+2"]
+
+view = traverse_ printExpr strs
+  where
+    printExpr s = do
+      let e = convertToExpr s
+      putStrLn $ show e ++ "=" ++ show (myeval e)
+
+exprs = map convertToExpr strs
+exprs' = map (convertToExpr . show) exprs
+
+check = and $ zipWith (\e1 e2 -> myeval e1 == myeval e2) exprs exprs'
+
+-- Converting expressions to prefix and postfix forms
+
+data ExprForm = Prefix | Postfix
+
+exprTo _ (Lit a) = show a
+exprTo form (Add e1 e2) = binOp "+" form e1 e2
+exprTo form (Mult e1 e2) = binOp "*" form e1 e2
+
+binOp op form e1 e2 = concat $ intersperse " " (args form) 
+   where
+     e1' = exprTo form e1
+     e2' = exprTo form e2
+     args Prefix = [op, e1', e2']
+     args Postfix = [e1', e2', op]
+
+main = do
+  view
+  putStr "Checked: "
+  print check
+  putStrLn "\nPrefix forms: "
+  mapM_ (putStrLn.exprTo Prefix) exprs
+  putStrLn "\nPostfix forms: "
+  mapM_ (putStrLn.exprTo Postfix) exprs
diff --git a/stref.hs b/stref.hs
new file mode 100644
--- /dev/null
+++ b/stref.hs
@@ -0,0 +1,33 @@
+import Data.Foldable (traverse_)
+import Control.Monad
+import Control.Monad.ST
+import Data.STRef
+
+comp1 :: ST s (STRef s Int)
+comp1 = do
+  -- ...
+  newSTRef 0
+
+comp2 :: STRef s Int -> ST s Int
+comp2 ref = do
+  -- ...
+  readSTRef ref
+
+
+--main = print $ runST (comp2 (runST comp1))
+
+countZeros :: [Int] -> Int
+countZeros = length . filter (== 0)
+
+countZerosST :: [Int] -> Int
+countZerosST xs = runST $ do
+   c <- newSTRef 0
+   traverse_ (\x -> when (x==0) $ inc c) xs
+   readSTRef c
+ where
+   inc c = modifySTRef' c (+1)
+
+main = do
+  print $ runST (comp1 >>= comp2)
+  print $ countZeros $ replicate 1000 0
+  print $ countZerosST $ replicate 1000 0
diff --git a/weapons.hs b/weapons.hs
new file mode 100644
--- /dev/null
+++ b/weapons.hs
@@ -0,0 +1,38 @@
+import Data.List (group, sort)
+import Control.Monad (replicateM)
+import Control.Monad.State
+import System.Random
+
+data Weapon = Rock | Paper | Scissors
+  deriving (Show, Bounded, Enum, Eq, Ord)
+
+data Winner = First | Second | Draw
+  deriving (Show, Eq, Ord)
+
+winner :: (Weapon, Weapon) -> Winner
+winner (Paper, Rock) = First
+winner (Scissors, Paper) = First
+winner (Rock, Scissors) = First
+winner (w1, w2) = if w1 == w2 then Draw else Second
+
+instance Random Weapon where
+    randomR (a,b) g = case randomR (fromEnum a, fromEnum b) g of
+                        (r, g') -> (toEnum r, g')
+    random g = randomR (minBound, maxBound) g
+
+
+randomWeapon :: State StdGen Weapon
+randomWeapon = state random
+
+gameRound :: State StdGen (Weapon, Weapon)
+gameRound = (,) <$> randomWeapon <*> randomWeapon
+
+game :: Int -> State StdGen [(Winner, Int)]
+game n = counts <$> replicateM n (winner <$> gameRound)
+  where
+    counts xs = map (\xs@(x:_) -> (x, length xs)) $ group $ sort xs
+    
+main = do
+  g <- newStdGen
+  let r = evalState (game 10) g
+  print r