Switch 'AT&T Park' to 'Oracle Park' on answer sheet

The word "do" seems to be missing in the final koan.

.gitignore

@@ -1,9 +1,206 @@
+*~
 bin
-classes
-lib
 releases
-target
 *.jar
-.DS_Store
+
+# Created by https://www.gitignore.io/api/clojure,osx,linux,windows,leiningen,intellij,eclipse,sublimetext
+
+### Clojure ###
+pom.xml
+pom.xml.asc
+*jar
+/lib/
+/classes/
+/target/
+/checkouts/
 .lein-deps-sum
-.lein-plugins
+.lein-repl-history
+.lein-plugins/
+.lein-failures
+.nrepl-port
+
+
+### OSX ###
+.DS_Store
+.AppleDouble
+.LSOverride
+
+# Icon must end with two \r
+Icon
+
+
+# Thumbnails
+._*
+
+# Files that might appear in the root of a volume
+.DocumentRevisions-V100
+.fseventsd
+.Spotlight-V100
+.TemporaryItems
+.Trashes
+.VolumeIcon.icns
+
+# Directories potentially created on remote AFP share
+.AppleDB
+.AppleDesktop
+Network Trash Folder
+Temporary Items
+.apdisk
+
+
+### Linux ###
+*~
+
+# KDE directory preferences
+.directory
+
+# Linux trash folder which might appear on any partition or disk
+.Trash-*
+
+
+### Windows ###
+# Windows image file caches
+Thumbs.db
+ehthumbs.db
+
+# Folder config file
+Desktop.ini
+
+# Recycle Bin used on file shares
+$RECYCLE.BIN/
+
+# Windows Installer files
+*.cab
+*.msi
+*.msm
+*.msp
+
+# Windows shortcuts
+*.lnk
+
+
+### Leiningen ###
+pom.xml
+pom.xml.asc
+*jar
+/lib/
+/classes/
+/target/
+/checkouts/
+.lein-deps-sum
+.lein-repl-history
+.lein-plugins/
+.lein-failures
+.nrepl-port
+
+
+### Intellij ###
+# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio
+
+*.iml
+
+## Directory-based project format:
+.idea/
+# if you remove the above rule, at least ignore the following:
+
+# User-specific stuff:
+# .idea/workspace.xml
+# .idea/tasks.xml
+# .idea/dictionaries
+
+# Sensitive or high-churn files:
+# .idea/dataSources.ids
+# .idea/dataSources.xml
+# .idea/sqlDataSources.xml
+# .idea/dynamic.xml
+# .idea/uiDesigner.xml
+
+# Gradle:
+# .idea/gradle.xml
+# .idea/libraries
+
+# Mongo Explorer plugin:
+# .idea/mongoSettings.xml
+
+## File-based project format:
+*.ipr
+*.iws
+
+## Plugin-specific files:
+
+# IntelliJ
+/out/
+
+# mpeltonen/sbt-idea plugin
+.idea_modules/
+
+# JIRA plugin
+atlassian-ide-plugin.xml
+
+# Crashlytics plugin (for Android Studio and IntelliJ)
+com_crashlytics_export_strings.xml
+crashlytics.properties
+crashlytics-build.properties
+
+
+### Eclipse ###
+*.pydevproject
+.metadata
+.gradle
+bin/
+tmp/
+*.tmp
+*.bak
+*.swp
+*~.nib
+local.properties
+.settings/
+.loadpath
+
+# Eclipse Core
+.project
+
+# External tool builders
+.externalToolBuilders/
+
+# Locally stored "Eclipse launch configurations"
+*.launch
+
+# CDT-specific
+.cproject
+
+# JDT-specific (Eclipse Java Development Tools)
+.classpath
+
+# Java annotation processor (APT)
+.factorypath
+
+# PDT-specific
+.buildpath
+
+# sbteclipse plugin
+.target
+
+# TeXlipse plugin
+.texlipse
+
+
+### SublimeText ###
+# cache files for sublime text
+*.tmlanguage.cache
+*.tmPreferences.cache
+*.stTheme.cache
+
+# workspace files are user-specific
+*.sublime-workspace
+
+# project files should be checked into the repository, unless a significant
+# proportion of contributors will probably not be using SublimeText
+# *.sublime-project
+
+# sftp configuration file
+sftp-config.json
+
+# Vagrant
+.vagrant/
+ubuntu-xenial-16.04-cloudimg-console.log

README.md

@@ -1,60 +1,88 @@
 # Clojure Koans
 
-The Clojure Koans are a fun and easy way to get started with Clojure - no
+The Clojure Koans are a fun way to get started with Clojure - no experience
-experience assumed or required.  Just follow the instructions below to start
+assumed or required. Follow the instructions below to start making tests pass!
-making tests pass!
 
 
-### Getting Started
+## Getting Started
 
-The easiest and fastest way to get the koans up and running is to [download the
+I recommend starting from a cloned or forked repo. This way you'll be able to
-latest zip file from Github](https://github.com/functional-koans/clojure-koans/downloads).
+track your progress in Git. You might want to create your own branch - that way
-This way, you'll have all the dependencies you need, including Clojure itself
+if you pull back the latest koans from master, it'll be a bit easier to manage
-and JLine, and you can skip the rest of this section (skip to "Running the
+the inevitable conflicts if we make changes to exercises you've already
-Koans").
+completed.
 
-If you're starting from a cloned or forked repo, that's cool too. This way
+You have a few options for installation:
-you'll be able to track your progress in Git, and see how your answers compare
+
-to others, by checking out the project's Network tab. You might want to create
+- Install the dependencies for the koans (such as Clojure) on your machine
-your own branch - that way if you pull back the latest koans from master, it'll
+- Use Vagrant and the configuration in this repository
-be a bit easier to manage the inevitable conflicts if we make changes to
+- Use Docker
-exercises you've already completed.
+
+Instructions for each option are below!
+
+
+### Installation on Your Machine
 
 The only things you'll need to run the Clojure Koans are:
 
-- JRE 1.5 or higher
+- JDK (I suggest version 8, but anything 6 or above should work fine)
-- [clojure-1.5.0.jar](http://repo1.maven.org/maven2/org/clojure/clojure/1.5.0/clojure-1.5.0.zip)
+- [Leiningen](http://github.com/technomancy/leiningen), a build tool for Clojure
 
-You can use [Leiningen](http://github.com/technomancy/leiningen) to
+Once you've cloned this repo and installed the dependencies, you can run:
-automatically install the Clojure jar in the right place. Leiningen will also
-get you a couple more jarfiles, including JLine, which allows you some of the
-functionality of readline (command-line history, for example).
 
-### Installing dependencies
+```
+lein repl
+```
 
-Dependencies are installed automatically with lein 2, but if you are still
+to make sure all the dependencies get downloaded properly (and then `(exit)`
-using lein 1 run
+when you want to quit). See below for details on the REPL.
-
-`lein deps`
-
-which will download all dependencies you need to run the Clojure koans.
 
 
-### Running the Koans
+### Installation with Vagrant
 
-If you're running from the zipfile or using lein 1, simply run
+Make sure you have [Vagrant](https://www.vagrantup.com/) and
+[VirtualBox](https://www.virtualbox.org) installed.
+In the root directory of the project, execute:
 
-`script/run` on Mac/\*nix
+```
+vagrant up
+vagrant ssh
+cd /vagrant
+lein koan run
+```
 
-`script\run` on Windows
 
-If you're running from a checkout using lein 2, run the koans via
+### Installation with Docker
+
+Once you've got [Docker](https://www.docker.com/) installed, you're basically
+all set. You can run these commands to get started:
+
+To run koans:
+
+```
+docker run --rm -it -v $(pwd):/app -w /app clojure lein koan run
+```
+
+To start up a REPL:
+
+```
+docker run --rm -it -v $(pwd):/app -w /app clojure lein repl
+```
+
+
+## Running the Koans
+
+Run the koans via:
 
 `lein koan run`
 
-It's an auto-runner, so as you save your files with the correct answers, it will
+If want to run directly from a REPL, once you are inside the `lein repl` prompt you can run the koans with
-advance you to the next koan or file (conveniently, all files are prefixed with
+
-the sequence that you should follow).
+`(exec "run")`
+
+Either way, it's an auto-runner, so as you save your files with the correct
+answers, it will advance you to the next koan or file (conveniently, all files
+are prefixed with the sequence that you should follow).
 
 You'll see something like this:
 
@@ -65,31 +93,33 @@ You'll see something like this:
     (= __ true)
 
 The output is telling you that you have a failing test in the file named
-`01_equalities.clj`, on line 3. So you just need to open that file up and make
+`01_equalities.clj`, on line 3. So you need to open that file up and make
 it pass!  You'll always be filling in the blanks to make tests pass.
 Sometimes there could be several correct answers (or even an infinite number):
-any of them will work in these cases.
+any of them will work in these cases. Some tests will pass even if you replace
+the blanks with whitespace (or nothing) instead of the expected answer. Make sure
+you give one correct expression to replace each blank.
 
 The koans differ from normal TDD in that the tests are already written for you,
 so you'll have to pay close attention to the failure messages, because up until
-the very end, making a test pass just means that the next failure message comes
+the very end, making a test pass means that the next failure message comes
 up.
 
-While it might be easy (especially at first) to just fill in the blanks making
+While it might be easy (especially at first) to fill in the blanks making
 things pass, you should work thoughtfully, making sure you understand why the
 answer is what it is.  Enjoy your path to Clojure enlightenment!
 
 
-### Trying more things out
+## Trying more things out
 
-There's a REPL (Read-Evaluate-Print Loop) included in the Clojure Koans. Just
+It's very useful to try things out in a REPL (Read-Evaluate-Print Loop)
-run:
+whenever you get stuck or curious. Run:
 
-`script/repl` on Mac/\*nix
+```
+lein repl
+```
 
-`script\repl` on Windows
+and you'll be able to type expressions in, and see what output they produce.
-
-If you're on lein 2, `lein repl` is what you want instead.
 
 Here are some interesting commands you might try, once you're in a running REPL:
 
@@ -108,42 +138,46 @@ And if those still don't make sense:
 
 will show you what those commands mean.
 
-You can exit the REPL with `CTRL-d` on any OS.
+You can exit the REPL with `CTRL-d`, `(exit)`, or `(quit)`.
 
 
-### Contributing
+## Contributing
 
 Patches are encouraged!  Make sure the answer sheet still passes
-(`script/test`, or `script\test` on Windows, or `lein koan test` on lein2), and
+(`lein koan test`), and send a pull request.
-send a pull request.
 
 The file ideaboard.txt has lots of good ideas for new koans to start, or things
 to add to existing koans.  So write some fun exercises, add your answers to
 `resources/koans.clj`, and we'll get them in there!
 
+Please follow the guidelines in
+http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html for
+commit messages, and put your code in a feature branch (not master) before
+making the pull request. This makes patches easier to review.
+
 Feel free to contact me (Colin Jones / trptcolin) on Github or elsewhere if you
 have any questions or want more direction before you start pitching in.
 
 
-### Contributors
+## Contributors
 
 https://github.com/functional-koans/clojure-koans/contributors
 
 
-### Credits
+## Credits
 
 These exercises were started by [Aaron Bedra](http://github.com/abedra) of
 [Relevance, Inc.](http://github.com/relevance) in early 2010, as a learning
 tool for newcomers to functional programming. Aaron's macro-fu makes these
-koans extremely simple and fun to use, and to improve upon, and without
+koans clear and fun to use and improve upon, and without Relevance's
-Relevance's initiative, this project would not exist.
+initiative, this project would not exist.
 
 Using the [koans](http://en.wikipedia.org/wiki/koan) metaphor as a tool for
 learning a programming language started with the
 [Ruby Koans](http://rubykoans.com) by [EdgeCase](http://github.com/edgecase).
 
 
-### License
+## License
 
 The use and distribution terms for this software are covered by the
 Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)

Vagrantfile

@@ -0,0 +1,31 @@
+Vagrant.configure("2") do |config|
+  config.vm.box = "ubuntu/xenial64"
+
+  config.vm.network "private_network", ip: "192.168.33.33"
+
+  config.vm.provider "virtualbox" do |vb|
+    vb.memory = "1024"
+  end
+
+  config.vm.provision "shell", inline: <<-SHELL
+    set -x
+
+    #apt-get update
+    #apt-get upgrade -y
+    apt-get install -y openjdk-8-jdk
+  SHELL
+
+  config.vm.provision "shell", privileged: false, inline: <<-SHELL
+      pwd
+      mkdir bin
+      echo "PATH=\$PATH:~/bin" >> .bashrc
+
+      cd bin
+      wget https://raw.githubusercontent.com/technomancy/leiningen/stable/bin/lein
+      chmod +x lein
+      ./lein
+
+      cd /vagrant
+      ~/bin/lein deps
+    SHELL
+end

ideaboard.txt

@@ -1,13 +1,16 @@
 Concepts / Language Features
 =====
+
 new record syntax
 Agents
 Vars
 state identity lifetime
-Metadata
 immutability / side effects
 type hints
 Pre and Post conditions of functions
+ex-info/ex-data
+reducers (?)
+transducers (?) - maybe just some basic ones, nothing too crazy
 
 Particular Functions
 =====
@@ -18,11 +21,9 @@ flatten
 
 frequencies
 reductions
-group-by
 keep
 keep-indexed
 map-indexed
 partition-all
 partition-by
 repeatedly
-

project.clj

@@ -1,8 +1,10 @@
-(defproject clojure-koans "0.4.9"
+(defproject clojure-koans "0.5.2-SNAPSHOT"
   :description "The Clojure koans."
-  :dependencies [[org.clojure/clojure "1.5.0"]
+  :dependencies [[org.clojure/clojure "1.10.0"]
-                 [koan-engine "0.2.0"]]
+                 [koan-engine "0.2.5"]]
-  :dev-dependencies [[lein-koan "0.1.2"]]
+  :dev-dependencies [[lein-koan "0.1.5"]]
-  :profiles {:dev {:dependencies [[lein-koan "0.1.2"]]}}
+  :profiles {:dev {:dependencies [[lein-koan "0.1.5"]]}}
-  :plugins [[lein-koan "0.1.2"]]
+  :repl-options {:init-ns koan-engine.runner
+                 :init ^:displace (do (use '[koan-engine.core]))}
+  :plugins [[lein-koan "0.1.5"]]
   :main koan-engine.runner/exec)

resources/koans.clj

@@ -1,77 +1,111 @@
 [["01_equalities" {"__" [true
                       2
-                      7
                       5
-                      4/2
+                      true
                       false
-                      6/3
+                      true
+                      true
+                      false
+                      "hello"
+                      "hello"
+                      nil
                       3]}]
 
- ["02_lists" {"__" [1 2 3 4 5
+ ["02_strings" {"__" ["hello"
+                "world"
+                "Cool "
+                "right?"
+                0
+                11
+                false
+                6 11
+                "123"
+                ", "
+                "1" "2" "3"
+                "olleh"
+                "hello"
+                13
+                nil
+                "hello world"
+                true
+                false
+                false
+                "a"
+                true
+                true
+                false]}]
+
+ ["03_lists" {"__" [1 2 3 4 5
                  1
                  [2 3 4 5]
+                 3
+                 0
                  ()
                  [:a :b :c :d :e]
-                 [0 :a :b :c :d :e]
+                 [:e :a :b :c :d]
                  :a
                  [:b :c :d :e]
                  "No dice!"
                  ()]}]
 
- ["03_vectors" {"__" [1
+ ["04_vectors" {"__" [1
-                   []
                    [1]
-                   [nil]
+                   [nil nil]
                    2
-                   [333]
+                   [111 222 333]
                    :peanut
                    :jelly
                    :jelly
                    [:butter :and]
                    3]}]
 
- ["04_sets" {"__" [nil
+ ["05_sets" {"__" [[3]
                 3
                 #{1 2 3 4 5}
                 #{1 2 3 4 5}
                 #{2 3}
                 #{1 4}]}]
 
- ["05_maps" {"__" [{}
+ ["06_maps" {"__" [:b 2
-                0
                 1
                 2
                 2
                 1
                 1
-                "Vancouver"
+                "Sochi"
                 nil
                 :key-not-found
                 true
                 false
                 "February"
                 1 "January"
-                2006 2010 2014
+                :c 3
-                "Vancouver"]}]
+                2
+                2010 2014 2018
+                "PyeongChang" "Sochi" "Vancouver"
+                2 3]}]
 
- ["06_functions" {"__" [20
+ ["07_functions" {"__" [81
-                     10 5
+                     20
-                     30 2
+                     10
+                     60
                      15
-                     20 *]
+                     "AACC"]
-               "___" [(fn [f] (f 5))
+               "___" [+
+                      *
+                      (fn [f] (f 5))
                       (fn [f] (f 5))]}]
 
- ["07_conditionals" {"__" [:a
+ ["08_conditionals" {"__" [:a
                         []
                         nil
                         :glory
                         4 6 :your-road
-                        'doom 0
+                        1
-                        :cocked-pistol
+                        :bicycling
-                        :say-what?]}]
+                        "is that even exercise?"]}]
 
- ["08_higher_order_functions" {"__" [4 8 12
+ ["09_higher_order_functions" {"__" [4 8 12
                                   (* x x)
                                   [false false true false false]
                                   ()
@@ -82,29 +116,29 @@
                                   100
                                   (count a) (count b)]}]
 
- ["09_runtime_polymorphism" {"__" [(str (:name a) " eats veggies.")
+ ["10_runtime_polymorphism" {"__" [(str (:name a) " eats veggies.")
                                 (str (:name a) " eats animals.")
                                 (str "I don't know what " (:name a) " eats.")
                                 "Hello World!"
                                 "Hello, you silly world."
                                 "Hello to this group: Peter, Paul, Mary!" ]}]
 
- ["10_lazy_sequences" {"__" [[1 2 3 4]
+ ["11_lazy_sequences" {"__" [[1 2 3 4]
                           [0 1 2 3 4]
                           10
                           95
-                          (range 20)
+                          [1 2 4 8 16 32 64 128]
                           :a]
-                    "___" [(fn [x] :foo)]}]
+                    "___" [(fn [x] x)]}]
 
- ["11_sequence_comprehensions" {"__" [[0 1 2 3 4 5]
+ ["12_sequence_comprehensions" {"__" [[0 1 2 3 4 5]
-                                   (* index index)
+                                   (* x x)
                                    (range 10)
-                                   (odd? index) (* index index)
+                                   (odd? x) (* x x)
                                    [row column]
                                    ]}]
 
- ["12_creating_functions" {"__" [true false true
+ ["13_creating_functions" {"__" [true false true
                               4
                               :a :b :c :d
                               :c :d
@@ -114,7 +148,7 @@
                                multiply-by-5
                                (comp dec square)]}]
 
- ["13_recursion" {"__" [true
+ ["14_recursion" {"__" [true
                      acc
                      (loop [coll coll
                             acc ()]
@@ -128,10 +162,10 @@
                          (recur (dec n) (* acc n))))]
                "___" [not]}]
 
- ["14_destructuring" {"__" [":bar:foo"
+ ["15_destructuring" {"__" [":bar:foo"
-                         (format (str "First comes %s, "
+                         (format (str "An Oxford comma list of %s, "
-                                      "then comes %s, "
+                                      "%s, "
-                                      "then comes %s with the baby carriage")
+                                      "and %s.")
                                  a b c)
                          (apply str
                                 (interpose " "
@@ -150,7 +184,7 @@
                                  street-address ", " city ", " state))
                           ]}]
 
- ["15_refs" {"__" ["hello"
+ ["16_refs" {"__" ["hello"
                 "hello"
                 "better"
                 "better!!!"
@@ -159,7 +193,7 @@
                 ]
           "___" [(fn [x] (+ 20 x))]}]
 
- ["16_atoms" {"__" [0
+ ["17_atoms" {"__" [0
                  1
                  (swap! atomic-clock (partial + 4))
                  20
@@ -167,17 +201,15 @@
                  atomic-clock 20 :fin
                  ]}]
 
- ["17_macros" {"__" [~(first form)
+ ["18_quote" {"__" ['(1 2 3 4 5)
-                  ~(nth form 2)
+                    (1 2 3 4 5)
-                  form
+                    'age
-                  (drop 2 form)
+                    quote
-                  "Hello, Macros!"
+                    '(+ 2 3)
-                  10
+                    1 2 3
-                  '(+ 9 1)
+                    1 5]}]
-                  '(* 10 2)
-                  '(+ 10 (2 * 3))]}]
 
- ["18_datatypes" {"__" [(print
+ ["19_datatypes" {"__" [(print
                       (str "You're really the "
                            (.category this)
                            ", " recipient "... sorry."))
@@ -189,18 +221,68 @@
                      (str "Congratulations on your Best Picture Oscar, "
                           "Evil Alien Conquerors!")]}]
 
- ["19_java_interop" {"__" [java.lang.String
+ ["20_java_interop" {"__" [java.lang.String
                         "SELECT * FROM"
                         10
                         1024
                         ]
                   "___" [#(.toUpperCase %)
-                         ]
+                         ]}]
-                  }]
+
- ["20_partition" {"__" [partition
+ ["21_partition" {"__" [partition
                         [:a :b :c]
                         '((0 1 2) (3 4))
                         5
                         :hello
-                        (6 :this :are)
+                        (6 :these :are)
-                        ]}]]
+                        ]}]
+
+ ["22_group_by" {"__" [odd?
+                       {5 ["hello" "world"] 3 ["foo" "bar"]}
+                       {1 [{:name "Bob" :id 1}
+                           {:last-name "Smith" :id 1}]
+                        2 [{:name "Jennifer" :id 2}]}
+                       nil
+                       {:naughty-list [{:name "Jimmy" :bad true}
+                                       {:name "Joe" :bad true}]
+                        :nice-list [{:name "Jane" :bad false}]}]}]
+
+ ["23_meta" {"__" [{:league "National League"}
+                   {:division "West"}
+                   "This doesn't implement the IObj interface"
+                   {:foo :bar}
+                   nil
+                   \C
+                   inc
+                   :park "Oracle Park"
+                   'Giants
+                   "Giants"]}]
+
+ ["24_macros" {"__" [~(first form)
+                     ~(nth form 2)
+                     form
+                     (drop 2 form)
+                     "Hello, Macros!"
+                     10
+                     '(+ 9 1)]}]
+
+ ["25_threading_macros" {"__" [{:a 1}
+                               "Hello world, and moon, and stars"
+                               "String with a trailing space"
+                               6
+                               1
+                               [2 3 4]
+                               12
+                               [1 2 3]]}]
+
+ ["26_transducers" {"__" ['(2 3 4)
+                          [2 4]
+                          [2 4]
+                          [2 4]
+                          6]}]
+
+ ["27_multimethods" {"__" ["Hello, World!"
+                           "Hello there"
+                           1
+                           6]}]
+]

script/deploy.sh

@@ -4,6 +4,8 @@ mkdir -p releases
 lein1 deps
 zip -r releases/clojure-koans-`date +"%Y-%m-%d_%H-%M"`.zip \
     . \
+    -x "./.idea/*" \
+    -x "./.lein-plugins/*" \
     -x "./.git/*" \
     -x "releases/*"
 

src/koans/01_equalities.clj

@@ -1,3 +1,6 @@
+(ns koans.01-equalities
+  (:require [koan-engine.core :refer :all]))
+
 (meditations
   "We shall contemplate truth by testing reality, via equality"
   (= __ true)
@@ -6,16 +9,31 @@
   (= __ (+ 1 1))
 
   "You can test equality of many things"
-  (= (+ 3 4) __ (+ 2 __))
+  (= (+ 3 4) 7 (+ 2 __))
 
   "Some things may appear different, but be the same"
-  (= 2 2/1 __)
+  (= __ (= 2 2/1))
 
   "You cannot generally float to heavens of integers"
   (= __ (= 2 2.0))
 
   "But a looser equality is also possible"
-  (== 2.0 2 __)
+  (= __ (== 2.0 2))
+
+  "Something is not equal to nothing"
+  (= __ (not (= 1 nil)))
+
+  "Strings, and keywords, and symbols: oh my!"
+  (= __ (= "hello" :hello 'hello))
+
+  "Make a keyword with your keyboard"
+  (= :hello (keyword __))
+
+  "Symbolism is all around us"
+  (= 'hello (symbol __))
+
+  "What could be equivalent to nothing?"
+  (= __ nil)
 
   "When things cannot be equal, they must be different"
   (not= :fill-in-the-blank __))

src/koans/02_strings.clj

@@ -0,0 +1,70 @@
+(ns koans.02-strings
+  (:require [koan-engine.core :refer :all]
+            [clojure.string :as string]))
+
+(meditations
+  "A string is nothing more than text surrounded by double quotes"
+  (= __ "hello")
+
+  "But double quotes are just magic on top of something deeper"
+  (= __ (str 'world))
+
+  "You can do more than create strings, you can put them together"
+  (= "Cool right?" (str __ __))
+
+  "You can even get certain characters"
+  (= \C (get "Characters" __))
+
+  "Or even count the characters"
+  (= __ (count "Hello World"))
+
+  "But strings and characters are not the same"
+  (= __ (= \c "c"))
+
+  "What if you only wanted to get part of a string?"
+  (= "World" (subs "Hello World" __ __))
+
+  "How about joining together elements in a list?"
+  (= __ (string/join '(1 2 3)))
+
+  "What if you wanted to separate them out?"
+  (= "1, 2, 3" (string/join __ '(1 2 3)))
+
+  "Maybe you want to separate out all your lines"
+  (= [__ __ __] (string/split-lines "1\n2\n3"))
+
+  "You may want to make sure your words are backwards"
+  (= __ (string/reverse "hello"))
+
+  "Maybe you want to find the index of the first occurrence of a substring"
+  (= 0 (string/index-of "hello world" __))
+
+  "Or maybe the last index of the same substring"
+  (= __ (string/last-index-of "hello world, hello" "hello"))
+
+  "But when something doesn't exist, nothing is found"
+  (= __ (string/index-of "hello world" "bob"))
+
+  "Sometimes you don't want whitespace cluttering the front and back"
+  (= __ (string/trim "  \nhello world \t \n"))
+
+  "You can check if something is a char"
+  (= __ (char? \c))
+
+  "But it may not be"
+  (= __ (char? "a"))
+
+  "But chars aren't strings"
+  (= __ (string? \b))
+
+  "Strings are strings"
+  (= true (string? __))
+
+  "Some strings may be blank"
+  (= __ (string/blank? ""))
+
+  "Even if at first glance they aren't"
+  (= __ (string/blank? " \n \t  "))
+
+  "However, most strings aren't blank"
+  (= __ (string/blank? "hello?\nare you out there?")))

src/koans/03_lists.clj

@@ -1,3 +1,6 @@
+(ns koans.03-lists
+  (:require [koan-engine.core :refer :all]))
+
 (meditations
   "Lists can be expressed by function or a quoted form"
   (= '(__ __ __ __ __) (list 1 2 3 4 5))
@@ -8,14 +11,20 @@
   "As well as the rest"
   (= __ (rest '(1 2 3 4 5)))
 
-  "The rest when nothing is left is empty"
+  "Count your blessings"
+  (= __ (count '(dracula dooku chocula)))
+
+  "Before they are gone"
+  (= __ (count '()))
+
+  "The rest, when nothing is left, is empty"
   (= __ (rest '(100)))
 
-  "And construction by adding an element to the front is simple"
+  "Construction by adding an element to the front is easy"
   (= __ (cons :a '(:b :c :d :e)))
 
-  "Conjoining an element to a list can be done in the reverse order"
+  "Conjoining an element to a list isn't hard either"
-  (= __ (conj '(:a :b :c :d :e) 0))
+  (= __ (conj '(:a :b :c :d) :e))
 
   "You can use a list like a stack to get the first element"
   (= __ (peek '(:a :b :c :d :e)))
@@ -26,9 +35,11 @@
   "But watch out if you try to pop nothing"
   (= __ (try
           (pop '())
-          (catch IllegalStateException e "No dice!")))
+          (catch IllegalStateException e
+            "No dice!")))
 
   "The rest of nothing isn't so strict"
   (= __ (try
           (rest '())
-          (catch IllegalStateException e "No dice!"))))
+          (catch IllegalStateException e
+            "No dice!"))))

src/koans/04_sets.clj

@@ -1,18 +0,0 @@
-(meditations
-  "You can create a set in two ways"
-  (= #{} (set __))
-
-  "They are another important data structure in clojure"
-  (= __ (count #{1 2 3}))
-
-  "Remember that a set is a 'set'"
-  (= __ (set '(1 1 2 2 3 3 4 4 5 5)))
-
-  "You can ask clojure for the union of two sets"
-  (= __ (clojure.set/union #{1 2 3 4} #{2 3 5}))
-
-  "And also the intersection"
-  (= __ (clojure.set/intersection #{1 2 3 4} #{2 3 5}))
-
-  "But don't forget about the difference"
-  (= __ (clojure.set/difference #{1 2 3 4 5} #{2 3 5})))

src/koans/04_vectors.clj

@@ -1,21 +1,21 @@
+(ns koans.04-vectors
+  (:require [koan-engine.core :refer :all]))
+
 (meditations
-  "You can use vectors in clojure to create an 'Array' like structure"
+  "You can use vectors in clojure as array-like structures"
   (= __ (count [42]))
 
-  "You can create a vector in several ways"
+  "You can create a vector from a list"
-  (= __ (vec nil))
-
-  "And populate it in either of these ways"
   (= __ (vec '(1)))
 
-  "There is another way as well"
+  "Or from some elements"
-  (= __ (vector nil))
+  (= __ (vector nil nil))
 
   "But you can populate it with any number of elements at once"
   (= [1 __] (vec '(1 2)))
 
-  "And add to it as well"
+  "Conjoining to a vector is different than to a list"
-  (= __ (conj (vec nil) 333))
+  (= __ (conj [111 222] 333))
 
   "You can get the first element of a vector like so"
   (= __ (first [:peanut :butter :and :jelly]))

src/koans/05_maps.clj

@@ -1,50 +0,0 @@
-(meditations
-  "There are two ways to create maps"
-  (= __ (hash-map))
-
-  "Maps in clojure associate keys with values"
-  (= __ (count (hash-map)))
-
-  "A value must be supplied for each key"
-  (= {:a 1} (hash-map :a __))
-
-  "The size is the number of entries"
-  (= __ (count {:a 1 :b 2}))
-
-  "You can look up the value for a given key"
-  (= __ (get {:a 1 :b 2} :b))
-
-  "Maps can be used as lookup functions"
-  (= __ ({:a 1 :b 2} :a))
-
-  "And so can keywords"
-  (= __ (:a {:a 1 :b 2}))
-
-  "But map keys need not be keywords"
-  (= __ ({2006 "Torino" 2010 "Vancouver" 2014 "Sochi"} 2010))
-
-  "You may not be able to find an entry for a key"
-  (= __ (get {:a 1 :b 2} :c))
-
-  "But you can provide your own default"
-  (= __ (get {:a 1 :b 2} :c :key-not-found))
-
-  "You can find out if a key is present"
-  (= __ (contains? {:a nil :b nil} :b))
-
-  "Or if it is missing"
-  (= __ (contains? {:a nil :b nil} :c))
-
-  "Maps are immutable, but you can create a new, 'changed' version"
-  (= {1 "January" 2 __} (assoc {1 "January" } 2 "February"))
-
-  "You can also 'remove' an entry"
-  (= {__ __} (dissoc {1 "January" 2 "February"} 2))
-
-  "Often you will need to get the keys (which will be in hash order)"
-  (= (list __ __ __)
-     (sort (keys {2006 "Torino" 2010 "Vancouver" 2014 "Sochi"})))
-
-  "Or the values"
-  (= (list "Sochi" "Torino" __)
-     (sort (vals {2006 "Torino" 2010 "Vancouver" 2014 "Sochi"}))))

src/koans/05_sets.clj

@@ -0,0 +1,22 @@
+(ns koans.05-sets
+  (:require [koan-engine.core :refer :all]
+            [clojure.set :as set]))
+
+(meditations
+  "You can create a set by converting another collection"
+  (= #{3} (set __))
+
+  "Counting them is like counting other collections"
+  (= __ (count #{1 2 3}))
+
+  "Remember that a set is a *mathematical* set"
+  (= __ (set '(1 1 2 2 3 3 4 4 5 5)))
+
+  "You can ask Clojure for the union of two sets"
+  (= __ (set/union #{1 2 3 4} #{2 3 5}))
+
+  "And also the intersection"
+  (= __ (set/intersection #{1 2 3 4} #{2 3 5}))
+
+  "But don't forget about the difference"
+  (= __ (set/difference #{1 2 3 4 5} #{2 3 5})))

src/koans/06_functions.clj

@@ -1,29 +0,0 @@
-(defn multiply-by-ten [n]
-  (* 10 n))
-
-(defn square [n] (* n n))
-
-(meditations
-  "Functions are often defined before they are used"
-  (= __ (multiply-by-ten 2))
-
-  "But they can also be defined inline"
-  (= __ ((fn [n] (* __ n)) 2))
-
-  "Or using even shorter syntax"
-  (= __ (#(* 15 %) __))
-
-  "Short anonymous functions may take multiple arguments"
-  (= __ (#(+ %1 %2 %3) 4 5 6))
-
-  "One function can beget another"
-  (= __ ((fn []
-           ((fn [a b] (__ a b))
-            4 5))))
-
-  "Higher-order functions take function arguments"
-  (= 25 (___
-         (fn [n] (* n n))))
-
-  "But they are often better written using the names of functions"
-  (= 25 (___ square)))

src/koans/06_maps.clj

@@ -0,0 +1,63 @@
+(ns koans.06-maps
+  (:require [koan-engine.core :refer :all]))
+
+(meditations
+  "Don't get lost when creating a map"
+  (= {:a 1 :b 2} (hash-map :a 1 __ __))
+
+  "A value must be supplied for each key"
+  (= {:a 1} (hash-map :a __))
+
+  "The size is the number of entries"
+  (= __ (count {:a 1 :b 2}))
+
+  "You can look up the value for a given key"
+  (= __ (get {:a 1 :b 2} :b))
+
+  "Maps can be used as functions to do lookups"
+  (= __ ({:a 1 :b 2} :a))
+
+  "And so can keywords"
+  (= __ (:a {:a 1 :b 2}))
+
+  "But map keys need not be keywords"
+  (= __ ({2010 "Vancouver" 2014 "Sochi" 2018 "PyeongChang"} 2014))
+
+  "You may not be able to find an entry for a key"
+  (= __ (get {:a 1 :b 2} :c))
+
+  "But you can provide your own default"
+  (= __ (get {:a 1 :b 2} :c :key-not-found))
+
+  "You can find out if a key is present"
+  (= __ (contains? {:a nil :b nil} :b))
+
+  "Or if it is missing"
+  (= __ (contains? {:a nil :b nil} :c))
+
+  "Maps are immutable, but you can create a new and improved version"
+  (= {1 "January" 2 __} (assoc {1 "January"} 2 "February"))
+
+  "You can also create a new version with an entry removed"
+  (= {__ __} (dissoc {1 "January" 2 "February"} 2))
+
+  "Create a new map by merging"
+  (= {:a 1 :b 2 __ __} (merge {:a 1 :b 2} {:c 3}))
+
+  "Specify how to handle entries with same keys when merging"
+  (= {:a 1 :b __ :c 3} (merge-with + {:a 1 :b 1} {:b 1 :c 3}))
+
+  "Often you will need to get the keys, but the order is undependable"
+  (= (list __ __ __)
+     (sort (keys { 2014 "Sochi" 2018 "PyeongChang" 2010 "Vancouver"})))
+
+  "You can get the values in a similar way"
+  (= (list __ __ __)
+     (sort (vals {2010 "Vancouver" 2014 "Sochi" 2018 "PyeongChang"})))
+
+  "You can even iterate over the map entries as a seq"
+  (= {:a __ :b __}
+     (into {}
+           (map
+            (fn [[k v]] [k (inc v)])
+            {:a 1 :b 2}))))

src/koans/07_functions.clj

@@ -0,0 +1,40 @@
+(ns koans.07-functions
+  (:require [koan-engine.core :refer :all]))
+
+(defn multiply-by-ten [n]
+  (* 10 n))
+
+(defn square [n] (* n n))
+
+(meditations
+  "Calling a function is like giving it a hug with parentheses"
+  (= __ (square 9))
+
+  "Functions are usually defined before they are used"
+  (= __ (multiply-by-ten 2))
+
+  "But they can also be defined inline"
+  (= __ ((fn [n] (* 5 n)) 2))
+
+  "Or using an even shorter syntax"
+  (= __ (#(* 15 %) 4))
+
+  "Even anonymous functions may take multiple arguments"
+  (= __ (#(+ %1 %2 %3) 4 5 6))
+
+  "Arguments can also be skipped"
+  (= __ (#(str "AA" %2) "bb" "CC"))
+
+  "One function can beget another"
+  (= 9 (((fn [] ___)) 4 5))
+
+  "Functions can also take other functions as input"
+  (= 20 ((fn [f] (f 4 5))
+           ___))
+
+  "Higher-order functions take function arguments"
+  (= 25 (___
+          (fn [n] (* n n))))
+
+  "But they are often better written using the names of functions"
+  (= 25 (___ square)))

src/koans/08_conditionals.clj

@@ -1,11 +1,12 @@
-(defn explain-defcon-level [exercise-term]
+(ns koans.08-conditionals
+  (:require [koan-engine.core :refer :all]))
+
+(defn explain-exercise-velocity [exercise-term]
   (case exercise-term
-        :fade-out          :you-and-what-army
+        :bicycling        "pretty fast"
-        :double-take       :call-me-when-its-important
+        :jogging          "not super fast"
-        :round-house       :o-rly
+        :walking          "not fast at all"
-        :fast-pace         :thats-pretty-bad
+        "is that even exercise?"))
-        :cocked-pistol     :sirens
-        :say-what?))
 
 (meditations
   "You will face many decisions"
@@ -33,14 +34,14 @@
                         :else __)))
 
   "Or your fate may be sealed"
-  (= __ (if-not (zero? __)
+  (= 'doom (if-not (zero? __)
           'doom
-          'doom))
+          'more-doom))
 
-  "In case of emergency, sound the alarms"
+  "In case of emergency, go fast"
-  (= :sirens
+  (= "pretty fast"
-     (explain-defcon-level __))
+     (explain-exercise-velocity __))
 
   "But admit it when you don't know what to do"
   (= __
-     (explain-defcon-level :yo-mama)))
+     (explain-exercise-velocity :watching-tv)))

src/koans/09_higher_order_functions.clj

@@ -1,3 +1,6 @@
+(ns koans.09-higher-order-functions
+  (:require [koan-engine.core :refer :all]))
+
 (meditations
   "The map function relates a sequence to another"
   (= [__ __ __] (map (fn [x] (* 4 x)) [1 2 3]))

src/koans/10_runtime_polymorphism.clj

@@ -1,9 +1,12 @@
+(ns koans.10-runtime-polymorphism
+  (:require [koan-engine.core :refer :all]))
+
 (defn hello
   ([] "Hello World!")
   ([a] (str "Hello, you silly " a "."))
   ([a & more] (str "Hello to this group: "
                    (apply str
-                          (interpose ", " (concat (list a) more)))
+                          (interpose ", " (cons a more)))
                    "!")))
 
 (defmulti diet (fn [x] (:eater x)))
@@ -26,6 +29,10 @@
   (= "Bambi eats veggies."
      (diet {:species "deer" :name "Bambi" :age 1 :eater :herbivore}))
 
+  "Animals have different names"
+  (= "Thumper eats veggies."
+     (diet {:species "rabbit" :name "Thumper" :age 1 :eater :herbivore}))
+
   "Different methods are used depending on the dispatch function result"
   (= "Simba eats animals."
      (diet {:species "lion" :name "Simba" :age 1 :eater :carnivore}))

src/koans/11_lazy_sequences.clj

@@ -1,3 +1,6 @@
+(ns koans.11-lazy-sequences
+  (:require [koan-engine.core :refer :all]))
+
 (meditations
   "There are many ways to generate a sequence"
   (= __ (range 1 5))
@@ -14,12 +17,12 @@
      (drop __ (range 100)))
 
   "Iteration provides an infinite lazy sequence"
-  (= __ (take 20 (iterate inc 0)))
+  (= __ (take 8 (iterate (fn [x] (* x 2)) 1)))
 
   "Repetition is key"
   (= [:a :a :a :a :a :a :a :a :a :a]
      (repeat 10 __))
 
   "Iteration can be used for repetition"
-  (= (repeat 100 :foo)
+  (= (repeat 100 "hello")
-     (take 100 (iterate ___ :foo))))
+     (take 100 (iterate ___ "hello"))))

src/koans/12_sequence_comprehensions.clj

@@ -1,27 +1,30 @@
+(ns koans.12-sequence-comprehensions
+  (:require [koan-engine.core :refer :all]))
+
 (meditations
   "Sequence comprehensions can bind each element in turn to a symbol"
   (= __
-     (for [index (range 6)]
+     (for [x (range 6)]
-       index))
+       x))
 
   "They can easily emulate mapping"
   (= '(0 1 4 9 16 25)
-     (map (fn [index] (* index index))
+     (map (fn [x] (* x x))
           (range 6))
-     (for [index (range 6)]
+     (for [x (range 6)]
        __))
 
   "And also filtering"
   (= '(1 3 5 7 9)
      (filter odd? (range 10))
-     (for [index __ :when (odd? index)]
+     (for [x __ :when (odd? x)]
-       index))
+       x))
 
-  "Combinations these transformations is trivial"
+  "Combinations of these transformations are trivial"
   (= '(1 9 25 49 81)
-     (map (fn [index] (* index index))
+     (map (fn [x] (* x x))
           (filter odd? (range 10)))
-     (for [index (range 10) :when __]
+     (for [x (range 10) :when __]
        __))
 
   "More complex transformations simply take multiple binding forms"

src/koans/13_creating_functions.clj

@@ -1,3 +1,6 @@
+(ns koans.13-creating-functions
+  (:require [koan-engine.core :refer :all]))
+
 (defn square [x] (* x x))
 
 (meditations

src/koans/14_recursion.clj

@@ -1,3 +1,6 @@
+(ns koans.14-recursion
+  (:require [koan-engine.core :refer :all]))
+
 (defn is-even? [n]
   (if (= n 0)
     __
@@ -29,13 +32,13 @@
   "Reversing directions is easy when you have not gone far"
   (= '(1) (recursive-reverse [1]))
 
-  "Yet more difficult the more steps you take"
+  "Yet it becomes more difficult the more steps you take"
-  (= '(5 4 3 2 1) (recursive-reverse [1 2 3 4 5]))
+  (= '(6 5 4 3 2) (recursive-reverse [2 3 4 5 6]))
 
-  "Simple things may appear simple."
+  "Simple things may appear simple"
   (= 1 (factorial 1))
 
-  "They may require other simple steps."
+  "They may require other simple steps"
   (= 2 (factorial 2))
 
   "Sometimes a slightly bigger step is necessary"

src/koans/15_destructuring.clj

@@ -1,3 +1,6 @@
+(ns koans.15-destructuring
+  (:require [koan-engine.core :refer :all]))
+
 (def test-address
   {:street-address "123 Test Lane"
    :city "Testerville"
@@ -9,24 +12,24 @@
          [:foo :bar]))
 
   "Whether in function definitions"
-  (= (str "First comes love, "
+  (= (str "An Oxford comma list of apples, "
-          "then comes marriage, "
+          "oranges, "
-          "then comes Clojure with the baby carriage")
+          "and pears.")
      ((fn [[a b c]] __)
-      ["love" "marriage" "Clojure"]))
+      ["apples" "oranges" "pears"]))
 
   "Or in let expressions"
-  (= "Rich Hickey aka The Clojurer aka Go Time aka Macro Killah"
+  (= "Rich Hickey aka The Clojurer aka Go Time aka Lambda Guru"
      (let [[first-name last-name & aliases]
-           (list "Rich" "Hickey" "The Clojurer" "Go Time" "Macro Killah")]
+           (list "Rich" "Hickey" "The Clojurer" "Go Time" "Lambda Guru")]
        __))
 
   "You can regain the full argument if you like arguing"
-  (= {:original-parts ["Steven" "Hawking"] :named-parts {:first "Steven" :last "Hawking"}}
+  (= {:original-parts ["Stephen" "Hawking"] :named-parts {:first "Stephen" :last "Hawking"}}
-     (let [[first-name last-name :as full-name] ["Steven" "Hawking"]]
+     (let [[first-name last-name :as full-name] ["Stephen" "Hawking"]]
        __))
 
-  "Break up maps by key"
+  "Break up maps by keys"
   (= "123 Test Lane, Testerville, TX"
      (let [{street-address :street-address, city :city, state :state} test-address]
        __))

src/koans/16_refs.clj

@@ -1,3 +1,6 @@
+(ns koans.16-refs
+  (:require [koan-engine.core :refer :all]))
+
 (def the-world (ref "hello"))
 (def bizarro-world (ref {}))
 

src/koans/17_atoms.clj

@@ -1,3 +1,6 @@
+(ns koans.17-atoms
+  (:require [koan-engine.core :refer :all]))
+
 (def atomic-clock (atom 0))
 
 (meditations
@@ -24,7 +27,7 @@
           (compare-and-set! atomic-clock 100 :fin)
           @atomic-clock))
 
-  "When your expectations are aligned with reality things, proceed that way"
+  "When your expectations are aligned with reality, things proceed that way"
   (= :fin (do
             (compare-and-set! __ __ __)
             @atomic-clock)))

src/koans/18_quote.clj

@@ -0,0 +1,25 @@
+(ns koans.18-quote
+  (:require [koan-engine.core :refer :all]))
+
+
+(meditations
+  "Wrap a quote around a list to suppress evaluation"
+  (= (quote (1 2 3 4 5)) __)
+
+  "There is a shortcut too!"
+  (= (quote __) '(1 2 3 4 5))
+
+  "You can quote symbols as well as lists... without evaluation!"
+  (= __ (let [age 9] (quote age)))
+
+  "You can use a literal list as a data collection without having Clojure try to call a function"
+  (= (cons 1 (__ (2 3))) (list 1 2 3) (cons 1 [2 3]))
+
+  "The quote affects all of its arguments, not just the top level"
+  (= (list 1 __) '(1 (+ 2 3)))
+
+  "Syntax-quote (`) acts similarly to the normal quote"
+  (= (list __ __ __) `(1 2 3) '(1 2 3))
+
+  "Unquote (~) within a syntax-quoted expression lets you mark specific expressions as requiring evaluation"
+  (= (list __ __) `(1 ~(+ 2 3)) '(1 5)))

src/koans/19_datatypes.clj

@@ -1,3 +1,6 @@
+(ns koans.19-datatypes
+  (:require [koan-engine.core :refer :all]))
+
 (defrecord Nobel [prize])
 (deftype Pulitzer [prize])
 

src/koans/20_java_interop.clj

@@ -1,3 +1,6 @@
+(ns koans.20-java-interop
+  (:require [koan-engine.core :refer :all]))
+
 (meditations
   "You may have done more with Java than you know"
   (= __ (class "warfare")) ; hint: try typing (javadoc "warfare") in the REPL

src/koans/21_partition.clj

@@ -1,3 +1,6 @@
+(ns koans.21-partition
+  (:require [koan-engine.core :refer :all]))
+
 (meditations
   "To split a collection you can use the partition function"
   (= '((0 1) (2 3)) (__ 2 (range 4)))
@@ -5,14 +8,14 @@
   "But watch out if there are not enough elements to form n sequences"
   (= '(__) (partition 3 [:a :b :c :d :e]))
 
-  "You can use partition-all to also get partitions with less then n elements"
+  "You can use partition-all to include any leftovers too"
   (= __ (partition-all 3 (range 5)))
 
   "If you need to, you can start each sequence with an offset"
   (= '((0 1 2) (5 6 7) (10 11 12)) (partition 3 __ (range 13)))
 
-  "Consider padding the last sequence with some default values.."
+  "Consider padding the last sequence with some default values"
   (= '((0 1 2) (3 4 5) (6 :hello)) (partition 3 3 [__] (range 7)))
 
-  ".. but notice that they will only pad up to given sequence length"
+  "But notice that they will only pad up to the given sequence length"
-  (= '((0 1 2) (3 4 5) __) (partition 3 3 [:this :are "my" "words"] (range 7))))
+  (= '((0 1 2) (3 4 5) __) (partition 3 3 [:these :are "my" "words"] (range 7))))

src/koans/22_group_by.clj

@@ -0,0 +1,36 @@
+(ns koans.22-group-by
+  (:require [koan-engine.core :refer :all]))
+
+(defn get-odds-and-evens [coll]
+  (let [{odds true evens false} (group-by __ coll)]
+    [odds evens]))
+
+(meditations
+  "To categorize a collection by some function, use group-by"
+  (= __ (group-by count ["hello" "world" "foo" "bar"]))
+
+  "You can simulate filter + remove in one pass"
+  (= (get-odds-and-evens [1 2 3 4 5])
+     ((juxt filter remove) odd? [1 2 3 4 5])
+     [[1 3 5] [2 4]])
+
+  "You can also group by a primary key"
+  (= __
+     (group-by :id [{:id 1 :name "Bob"}
+                    {:id 2 :name "Jennifer"}
+                    {:id 1 :last-name "Smith"} ]))
+
+  "But be careful when you group by a non-required key"
+  (= {"Bob" [{:name "Bob" :id 1}]
+      "Jennifer" [{:name "Jennifer" :id 2}]
+      __ [{:last-name "Smith" :id 1}]}
+   (group-by :name [{:id 1 :name "Bob"}
+                    {:id 2 :name "Jennifer"}
+                    {:id 1 :last-name "Smith"}]))
+
+  "The true power of group-by comes with custom functions"
+  (= __
+     (group-by #(if (:bad %) :naughty-list :nice-list)
+               [{:name "Jimmy" :bad true}
+                {:name "Jane" :bad false}
+                {:name "Joe" :bad true}])))

src/koans/23_meta.clj

@@ -0,0 +1,51 @@
+(ns koans.23-meta
+  (:require [koan-engine.core :refer :all]))
+
+(def giants
+  (with-meta 'Giants
+    {:league "National League"}))
+
+(meditations
+  "Some objects can be tagged using the with-meta function"
+  (= __ (meta giants))
+
+  "Or more succinctly with a reader macro"
+  (= __ (meta '^{:division "West"} Giants))
+
+  "While others can't"
+  (= __ (try
+          (with-meta
+            2
+            {:prime true})
+          (catch ClassCastException e
+            "This doesn't implement the IObj interface")))
+
+  "Notice when metadata carries over"
+  (= __ (meta (merge '^{:foo :bar} {:a 1 :b 2}
+                     {:b 3 :c 4})))
+
+  "And when it doesn't"
+  (= __ (meta (merge {:a 1 :b 2}
+                     '^{:foo :bar} {:b 3 :c 4})))
+
+  "Metadata can be used as a type hint to avoid reflection during runtime"
+  (= __ (#(.charAt ^String % 0) "Cast me"))
+
+  "You can directly update an object's metadata"
+  (= 8 (let [giants
+             (with-meta
+               'Giants
+               {:world-series-titles (atom 7)})]
+         (swap! (:world-series-titles (meta giants)) __)
+         @(:world-series-titles (meta giants))))
+
+  "You can also create a new object from another object with metadata"
+  (= {:league "National League" :park "Oracle Park"}
+     (meta (vary-meta giants
+                      assoc __ __)))
+
+  "But it won't affect behavior like equality"
+  (= __ (vary-meta giants dissoc :league))
+
+  "Or the object's printed representation"
+  (= __ (pr-str (vary-meta giants dissoc :league))))

src/koans/24_macros.clj

@@ -1,26 +1,29 @@
+(ns koans.24-macros
+  (:require [koan-engine.core :refer :all]))
+
 (defmacro hello [x]
   (str "Hello, " x))
 
 (defmacro infix [form]
   (list (second form) (first form) (nth form 2)))
 
-(defmacro infix-better [form]
+(defmacro infix-concise [form]
   `(~(second form) ; Note the syntax-quote (`) and unquote (~) characters!
     __
     __))
 
-(defmacro r-infix [form]
+(defmacro recursive-infix [form]
   (cond (not (seq? form))
         __
         (= 1 (count form))
-        `(r-infix ~(first form))
+        `(recursive-infix ~(first form))
         :else
         (let [operator (second form)
               first-arg (first form)
               others __]
           `(~operator
-            (r-infix ~first-arg)
+            (recursive-infix ~first-arg)
-            (r-infix ~others)))))
+            (recursive-infix ~others)))))
 
 (meditations
   "Macros are like functions created at compile time"
@@ -33,10 +36,10 @@
   (= __ (macroexpand '(infix (9 + 1))))
 
   "You can do better than that - hand crafting FTW!"
-  (= __ (macroexpand '(infix-better (10 * 2))))
+  (= '(* 10 2) (macroexpand '(infix-concise (10 * 2))))
 
-  "Things don't always work as you would like them to... "
+  "Things don't always work as you would like them to"
-  (= __ (macroexpand '(infix-better ( 10 + (2 * 3)))))
+  (= '(+ 10 (2 * 3)) (macroexpand '(infix-concise (10 + (2 * 3)))))
 
   "Really, you don't understand recursion until you understand recursion"
-  (= 36 (r-infix (10 + (2 * 3) + (4 * 5)))))
+  (= 36 (recursive-infix (10 + (2 * 3) + (4 * 5)))))

src/koans/25_threading_macros.clj

@@ -0,0 +1,66 @@
+(ns koans.25-threading-macros
+  (:require [koan-engine.core :refer :all]))
+
+(def a-list
+  '(1 2 3 4 5))
+
+(def a-list-with-maps
+  '({:a 1} {:a 2} {:a 3}))
+
+(defn function-that-takes-a-map [map a b]
+  (get map :a))
+
+(defn function-that-takes-a-coll [a b coll]
+  (map :a coll))
+
+(meditations
+ "We can use thread first for more readable sequential operations"
+ (= __
+    (-> {}
+        (assoc :a 1)))
+
+ "Consider also the case of strings"
+ (= __
+    (-> "Hello world"
+        (str ", and moon")
+        (str ", and stars")))
+
+ "When a function has no arguments to partially apply, just reference it"
+ (= __
+    (-> "String with a trailing space "
+        clojure.string/trim))
+
+ "Most operations that take a scalar value as an argument can be threaded-first"
+ (= __
+    (-> {}
+        (assoc :a 1)
+        (assoc :b 2)
+        (assoc :c {:d 4
+                   :e 5})
+        (update-in [:c :e] inc)
+        (get-in [:c :e])))
+
+ "We can use functions we have written ourselves that follow this pattern"
+ (= __
+    (-> {}
+        (assoc :a 1)
+        (function-that-takes-a-map "hello" "there")))
+
+ "We can also thread last using ->>"
+ (= __
+    (->> [1 2 3]
+         (map inc)))
+
+ "Most operations that take a collection can be threaded-last"
+ (= __
+    (->> a-list
+         (map inc)
+         (filter even?)
+         (into [])
+         (reduce +)))
+
+ "We can use functions we have written ourselves that follow this pattern"
+ (= __
+    (->> a-list-with-maps
+         (function-that-takes-a-coll "hello" "there")
+         (into []))))

src/koans/26_transducers.clj

@@ -0,0 +1,30 @@
+(ns koans.26-transducers
+  (:require [koan-engine.core :refer :all]))
+
+(def example-transducer
+  (map inc))
+
+(def transforms
+  (comp (map inc)
+     (filter even?)))
+
+(meditations
+ "A sequence operation with only one argument often returns a transducer"
+ (= __
+    (sequence example-transducer [1 2 3]))
+
+ "Consider that sequence operations can be composed as transducers"
+ (= __
+    (transduce transforms conj [1 2 3]))
+
+ "We can do this eagerly"
+ (= __
+    (into [] transforms [1 2 3]))
+
+ "Or lazily"
+ (= __
+    (sequence transforms [1 2 3]))
+
+ "The transduce function can combine mapping and reduction"
+ (= __
+    (transduce transforms + [1 2 3])))

src/koans/27_multimethods.clj

@@ -0,0 +1,44 @@
+(ns koans.27-multimethods
+  (:require [koan-engine.core :refer :all]))
+
+(defmulti multimethod-without-args
+ (fn [keyword-arg] keyword-arg))
+
+(defmethod multimethod-without-args :first [_]
+ (str "Hello, World!"))
+
+(defmethod multimethod-without-args :second [_]
+ (str "Hello there"))
+
+(defmulti multimethod-with-args
+ (fn [opt-one opt-two] opt-one))
+
+(defmethod multimethod-with-args :path-one [_ opts]
+ (:first-opt opts))
+
+(defmethod multimethod-with-args :path-two [_ opts]
+ (let [numbers (:second-opt opts)]
+  (->> numbers
+       (map inc)
+       (reduce +))))
+
+(defmethod multimethod-with-args :path-three [_])
+
+(meditations
+ "A multimethod takes one or more arguments to dispatch on"
+ (= __
+    (multimethod-without-args :first))
+
+ "Though it can be ignored and represented by _ in defmethods"
+ (= __
+    (multimethod-without-args :second))
+
+ "Alternatively, we can use the arguments in defmethods"
+ (= __
+    (multimethod-with-args :path-one {:first-opt 1
+                                      :second-opt 2}))
+ 
+ "This allows us to do something different in each method implementation"
+ (= __
+    (multimethod-with-args :path-two {:first-opt 1
+                                      :second-opt [0 1 2]})))