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*~
bin
releases
*.jar
# 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-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

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README.md
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# Clojure Koans
The Clojure Koans are a fun way to get started with Clojure - no experience
assumed or required. Follow the instructions below to start making tests pass!
## Getting Started
I recommend starting from a cloned or forked repo. This way you'll be able to
track your progress in Git. You might want to create your own branch - that way
if you pull back the latest koans from master, it'll be a bit easier to manage
the inevitable conflicts if we make changes to exercises you've already
completed.
You have a few options for installation:
- Install the dependencies for the koans (such as Clojure) on your machine
- Use Vagrant and the configuration in this repository
- Use Docker
Instructions for each option are below!
### Installation on Your Machine
The only things you'll need to run the Clojure Koans are:
- JDK (I suggest version 8, but anything 6 or above should work fine)
- [Leiningen](http://github.com/technomancy/leiningen), a build tool for Clojure
Once you've cloned this repo and installed the dependencies, you can run:
```
lein repl
```
to make sure all the dependencies get downloaded properly (and then `(exit)`
when you want to quit). See below for details on the REPL.
### Installation with Vagrant
Make sure you have [Vagrant](https://www.vagrantup.com/) and
[VirtualBox](https://www.virtualbox.org) installed.
In the root directory of the project, execute:
```
vagrant up
vagrant ssh
cd /vagrant
lein koan run
```
### 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 $(pwd):/app -w /app clojure lein repl
```
## Running the Koans
Run the koans via:
`lein koan run`
If want to run directly from a REPL, once you are inside the `lein repl` prompt you can run the koans with
`(exec "run")`
Either way, it's an auto-runner, so as you save your files with the correct
answers, it will advance you to the next koan or file (conveniently, all files
are prefixed with the sequence that you should follow).
You'll see something like this:
Now meditate on /home/colin/Projects/clojure-koans/src/koans/01_equalities.clj:3
---------------------
Assertion failed!
We shall contemplate truth by testing reality, via equality.
(= __ true)
The output is telling you that you have a failing test in the file named
`01_equalities.clj`, on line 3. So you need to open that file up and make
it pass! You'll always be filling in the blanks to make tests pass.
Sometimes there could be several correct answers (or even an infinite number):
any of them will work in these cases. Some tests will pass even if you replace
the blanks with whitespace (or nothing) instead of the expected answer. Make sure
you give one correct expression to replace each blank.
The koans differ from normal TDD in that the tests are already written for you,
so you'll have to pay close attention to the failure messages, because up until
the very end, making a test pass means that the next failure message comes
up.
While it might be easy (especially at first) to fill in the blanks making
things pass, you should work thoughtfully, making sure you understand why the
answer is what it is. Enjoy your path to Clojure enlightenment!
## Trying more things out
It's very useful to try things out in a REPL (Read-Evaluate-Print Loop)
whenever you get stuck or curious. Run:
```
lein repl
```
and you'll be able to type expressions in, and see what output they produce.
Here are some interesting commands you might try, once you're in a running REPL:
```clojure
(find-doc "vec")
(find-doc #"vec$")
(doc vec)
```
And if those still don't make sense:
```clojure
(doc doc)
(doc find-doc)
```
will show you what those commands mean.
You can exit the REPL with `CTRL-d`, `(exit)`, or `(quit)`.
## Contributing
Patches are encouraged! Make sure the answer sheet still passes
(`lein koan test`), and 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
https://github.com/functional-koans/clojure-koans/contributors
## 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 clear and fun to use and improve upon, and without Relevance's
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
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)
which can be found in the file epl-v10.html at the root of this distribution.
By using this software in any fashion, you are agreeing to be bound by
the terms of this license.

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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

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ideaboard.txt
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Concepts / Language Features
=====
new record syntax
Agents
Vars
state identity lifetime
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
=====
fnil - creating_a_function
juxt - creating_a_function
constantly - creating_a_function
flatten
frequencies
reductions
keep
keep-indexed
map-indexed
partition-all
partition-by
repeatedly

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<!DOCTYPE html>
<html>
<head>
<meta charset='utf-8'>
<title>functional-koans/clojure-koans @ GitHub</title>
<style type="text/css">
body {
margin-top: 1.0em;
background-color: #186bd8;
font-family: Helvetica, Arial, FreeSans, san-serif;
color: #ffffff;
}
#container {
margin: 0 auto;
width: 700px;
}
h1 { font-size: 3.8em; color: #e79427; margin-bottom: 3px; }
h1 .small { font-size: 0.4em; }
h1 a { text-decoration: none }
h2 { font-size: 1.5em; color: #e79427; }
h3 { text-align: center; color: #e79427; }
a { color: #e79427; }
.description { font-size: 1.2em; margin-bottom: 30px; margin-top: 30px; font-style: italic;}
.download { float: right; }
pre { background: #000; color: #fff; padding: 15px;}
hr { border: 0; width: 80%; border-bottom: 1px solid #aaa}
.footer { text-align:center; padding-top:30px; font-style: italic; }
</style>
</head>
<body>
<a href="http://github.com/functional-koans/clojure-koans"><img style="position: absolute; top: 0; right: 0; border: 0;" src="http://s3.amazonaws.com/github/ribbons/forkme_right_darkblue_121621.png" alt="Fork me on GitHub" /></a>
<div id="container">
<div class="download">
<a href="http://github.com/functional-koans/clojure-koans/zipball/master">
<img border="0" width="90" src="http://github.com/images/modules/download/zip.png"></a>
<a href="http://github.com/functional-koans/clojure-koans/tarball/master">
<img border="0" width="90" src="http://github.com/images/modules/download/tar.png"></a>
</div>
<h1><a href="http://github.com/functional-koans/clojure-koans">clojure-koans</a>
<span class="small">by <a href="http://github.com/functional-koans">functional-koans</a></span></h1>
<div class="description">
A set of exercises for learning Clojure
</div>
<h2>Authors</h2>
<p>Aaron Bedra (aaron@aaronbedra.com)
<br/>Alex Robbins (alexander.j.robbins@gmail.com)
<br/>calebphillips (caleb.phillips@gmail.com)
<br/>Michael Kohl (citizen428@gmail.com)
<br/>Eric Lavigne (lavigne.eric@gmail.com)
<br/>Jaskirat (me@jaskirat.info)
<br/>Micah (micah@8thlight.com)
<br/>Nuno Marques (nuno@platogo.com)
<br/>Colin Jones and Mike Jansen (pair@8thlight.com)
<br/>Colin Jones (trptcolin@gmail.com)
<br/>Mark Simpson (verdammelt@gmail.com)
<br/>
<br/> </p>
<h2>Contact</h2>
<p> (trptcolin@gmail.com)
<br/> </p>
<h2>Download</h2>
<p>
You can download this project in either
<a href="http://github.com/functional-koans/clojure-koans/zipball/master">zip</a> or
<a href="http://github.com/functional-koans/clojure-koans/tarball/master">tar</a> formats.
</p>
<p>You can also clone the project with <a href="http://git-scm.com">Git</a>
by running:
<pre>$ git clone git://github.com/functional-koans/clojure-koans</pre>
</p>
<div class="footer">
get the source code on GitHub : <a href="http://github.com/functional-koans/clojure-koans">functional-koans/clojure-koans</a>
</div>
</div>
</body>
</html>

10
project.clj
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@ -1,10 +0,0 @@
(defproject clojure-koans "0.5.2-SNAPSHOT"
:description "The Clojure koans."
:dependencies [[org.clojure/clojure "1.10.0"]
[koan-engine "0.2.5"]]
:dev-dependencies [[lein-koan "0.1.5"]]
:profiles {:dev {:dependencies [[lein-koan "0.1.5"]]}}
: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)

288
resources/koans.clj
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@ -1,288 +0,0 @@
[["01_equalities" {"__" [true
2
5
true
false
true
true
false
"hello"
"hello"
nil
3]}]
["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]
[:e :a :b :c :d]
:a
[:b :c :d :e]
"No dice!"
()]}]
["04_vectors" {"__" [1
[1]
[nil nil]
2
[111 222 333]
:peanut
:jelly
:jelly
[:butter :and]
3]}]
["05_sets" {"__" [[3]
3
#{1 2 3 4 5}
#{1 2 3 4 5}
#{2 3}
#{1 4}]}]
["06_maps" {"__" [:b 2
1
2
2
1
1
"Sochi"
nil
:key-not-found
true
false
"February"
1 "January"
:c 3
2
2010 2014 2018
"PyeongChang" "Sochi" "Vancouver"
2 3]}]
["07_functions" {"__" [81
20
10
60
15
"AACC"]
"___" [+
*
(fn [f] (f 5))
(fn [f] (f 5))]}]
["08_conditionals" {"__" [:a
[]
nil
:glory
4 6 :your-road
1
:bicycling
"is that even exercise?"]}]
["09_higher_order_functions" {"__" [4 8 12
(* x x)
[false false true false false]
()
[:anything :goes :here]
(< x 31)
(* 10 x) (< x 4)
24
100
(count a) (count b)]}]
["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!" ]}]
["11_lazy_sequences" {"__" [[1 2 3 4]
[0 1 2 3 4]
10
95
[1 2 4 8 16 32 64 128]
:a]
"___" [(fn [x] x)]}]
["12_sequence_comprehensions" {"__" [[0 1 2 3 4 5]
(* x x)
(range 10)
(odd? x) (* x x)
[row column]
]}]
["13_creating_functions" {"__" [true false true
4
:a :b :c :d
:c :d
4
8]
"___" [(complement nil?)
multiply-by-5
(comp dec square)]}]
["14_recursion" {"__" [true
acc
(loop [coll coll
acc ()]
(if (seq coll)
(recur (rest coll) (conj acc (first coll)))
acc))
(loop [n n
acc 1]
(if (zero? n)
acc
(recur (dec n) (* acc n))))]
"___" [not]}]
["15_destructuring" {"__" [":bar:foo"
(format (str "An Oxford comma list of %s, "
"%s, "
"and %s.")
a b c)
(apply str
(interpose " "
(apply list
first-name
last-name
(interleave (repeat "aka") aliases))))
{:original-parts full-name
:named-parts {:first first-name :last last-name}}
(str street-address ", " city ", " state)
city state
(str street-address ", " city ", " state)]
"___" [(fn [[fname lname]
{:keys [street-address city state]}]
(str fname " " lname ", "
street-address ", " city ", " state))
]}]
["16_refs" {"__" ["hello"
"hello"
"better"
"better!!!"
(dosync (ref-set the-world 0))
(map :jerry [@the-world @bizarro-world])
]
"___" [(fn [x] (+ 20 x))]}]
["17_atoms" {"__" [0
1
(swap! atomic-clock (partial + 4))
20
20
atomic-clock 20 :fin
]}]
["18_quote" {"__" ['(1 2 3 4 5)
(1 2 3 4 5)
'age
quote
'(+ 2 3)
1 2 3
1 5]}]
["19_datatypes" {"__" [(print
(str "You're really the "
(.category this)
", " recipient "... sorry."))
"peace"
"literature"
"physics"
nil
[true false]
(str "Congratulations on your Best Picture Oscar, "
"Evil Alien Conquerors!")]}]
["20_java_interop" {"__" [java.lang.String
"SELECT * FROM"
10
1024
]
"___" [#(.toUpperCase %)
]}]
["21_partition" {"__" [partition
[:a :b :c]
'((0 1 2) (3 4))
5
:hello
(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]}]
]

18
script/deploy.sh
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@ -1,18 +0,0 @@
#!/bin/sh
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/*"
echo
echo "Don't forget to upload the zipfile (somewhere...)"
echo `ls -t releases/clojure-koans-*.zip | head -n1`
echo "git push"
echo "git push --tags"
echo

12
script/repl
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@ -1,12 +0,0 @@
#!/bin/sh
CLASSPATH=src
for f in lib/*.jar lib/dev/*.jar resources/; do
CLASSPATH=$CLASSPATH:$f
done
if [ "$OSTYPE" = "cygwin" ]; then
CLASSPATH=`cygpath -wp $CLASSPATH`
fi
java -Xmx1G -cp $CLASSPATH jline.ConsoleRunner clojure.main

14
script/repl.bat
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@ -1,14 +0,0 @@
@echo off
setLocal EnableDelayedExpansion
set CLASSPATH="
for %%j in (".\lib\*.jar") do (
set CLASSPATH=!CLASSPATH!;%%~fj
)
set CLASSPATH=!CLASSPATH!"
set CLASSPATH=%CLASSPATH%;src;resources
set JLINE=jline.ConsoleRunner
java -Xmx1G -cp %CLASSPATH% %JLINE% clojure.main

13
script/run
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@ -1,13 +0,0 @@
#!/bin/sh
CLASSPATH=src
for f in lib/*.jar lib/dev/*.jar resources/; do
CLASSPATH=$CLASSPATH:$f
done
if [ "$OSTYPE" = "cygwin" ]; then
CLASSPATH=`cygpath -wp $CLASSPATH`
fi
java -cp "$CLASSPATH" clojure.main script/run.clj
echo

12
script/run.bat
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@ -1,12 +0,0 @@
@echo off
setLocal EnableDelayedExpansion
set CLASSPATH="
for %%j in (".\lib\*.jar", ".\lib\dev\*.jar") do (
set CLASSPATH=!CLASSPATH!;%%~fj
)
set CLASSPATH=!CLASSPATH!"
set CLASSPATH=%CLASSPATH%;src;resources
java -Xmx1G -cp %CLASSPATH% clojure.main script\run.clj

2
script/run.clj
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@ -1,2 +0,0 @@
(require 'koan-engine.runner)
(koan-engine.runner/exec "run")

14
script/test
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@ -1,14 +0,0 @@
#!/bin/sh
CLASSPATH=src
for f in lib/*.jar lib/dev/*.jar resources/; do
CLASSPATH=$CLASSPATH:$f
done
if [ "$OSTYPE" = "cygwin" ]; then
CLASSPATH=`cygpath -wp $CLASSPATH`
fi
java -cp "$CLASSPATH" clojure.main script/test.clj
echo

11
script/test.bat
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@ -1,11 +0,0 @@
@echo off
setLocal EnableDelayedExpansion
set CLASSPATH="
for %%j in (".\lib\*.jar", ".\lib\dev\*.jar") do (
set CLASSPATH=!CLASSPATH!;%%~fj
)
set CLASSPATH=!CLASSPATH!"
set CLASSPATH=%CLASSPATH%;src;resources
java -Xmx1G -cp %CLASSPATH% clojure.main script\test.clj

2
script/test.clj
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@ -1,2 +0,0 @@
(require 'koan-engine.runner)
(koan-engine.runner/exec "test")

39
src/koans/01_equalities.clj
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@ -1,39 +0,0 @@
(ns koans.01-equalities
(:require [koan-engine.core :refer :all]))
(meditations
"We shall contemplate truth by testing reality, via equality"
(= __ true)
"To understand reality, we must compare our expectations against reality"
(= __ (+ 1 1))
"You can test equality of many things"
(= (+ 3 4) 7 (+ 2 __))
"Some things may appear different, but be the same"
(= __ (= 2 2/1))
"You cannot generally float to heavens of integers"
(= __ (= 2 2.0))
"But a looser equality is also possible"
(= __ (== 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 __))

70
src/koans/02_strings.clj
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@ -1,70 +0,0 @@
(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?")))

45
src/koans/03_lists.clj
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@ -1,45 +0,0 @@
(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))
"They are Clojure seqs (sequences), so they allow access to the first"
(= __ (first '(1 2 3 4 5)))
"As well as the rest"
(= __ (rest '(1 2 3 4 5)))
"Count your blessings"
(= __ (count '(dracula dooku chocula)))
"Before they are gone"
(= __ (count '()))
"The rest, when nothing is left, is empty"
(= __ (rest '(100)))
"Construction by adding an element to the front is easy"
(= __ (cons :a '(:b :c :d :e)))
"Conjoining an element to a list isn't hard either"
(= __ (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)))
"Or the others"
(= __ (pop '(:a :b :c :d :e)))
"But watch out if you try to pop nothing"
(= __ (try
(pop '())
(catch IllegalStateException e
"No dice!")))
"The rest of nothing isn't so strict"
(= __ (try
(rest '())
(catch IllegalStateException e
"No dice!"))))

33
src/koans/04_vectors.clj
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@ -1,33 +0,0 @@
(ns koans.04-vectors
(:require [koan-engine.core :refer :all]))
(meditations
"You can use vectors in clojure as array-like structures"
(= __ (count [42]))
"You can create a vector from a list"
(= __ (vec '(1)))
"Or from some elements"
(= __ (vector nil nil))
"But you can populate it with any number of elements at once"
(= [1 __] (vec '(1 2)))
"Conjoining to a vector is different than to a list"
(= __ (conj [111 222] 333))
"You can get the first element of a vector like so"
(= __ (first [:peanut :butter :and :jelly]))
"And the last in a similar fashion"
(= __ (last [:peanut :butter :and :jelly]))
"Or any index if you wish"
(= __ (nth [:peanut :butter :and :jelly] 3))
"You can also slice a vector"
(= __ (subvec [:peanut :butter :and :jelly] 1 3))
"Equality with collections is in terms of values"
(= (list 1 2 3) (vector 1 2 __)))

22
src/koans/05_sets.clj
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@ -1,22 +0,0 @@
(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})))

63
src/koans/06_maps.clj
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@ -1,63 +0,0 @@
(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}))))

40
src/koans/07_functions.clj
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@ -1,40 +0,0 @@
(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)))

47
src/koans/08_conditionals.clj
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@ -1,47 +0,0 @@
(ns koans.08-conditionals
(:require [koan-engine.core :refer :all]))
(defn explain-exercise-velocity [exercise-term]
(case exercise-term
:bicycling "pretty fast"
:jogging "not super fast"
:walking "not fast at all"
"is that even exercise?"))
(meditations
"You will face many decisions"
(= __ (if (false? (= 4 5))
:a
:b))
"Some of them leave you no alternative"
(= __ (if (> 4 3)
[]))
"And in such a situation you may have nothing"
(= __ (if (nil? 0)
[:a :b :c]))
"In others your alternative may be interesting"
(= :glory (if (not (empty? ()))
:doom
__))
"You may have a multitude of possible paths"
(let [x 5]
(= :your-road (cond (= x __) :road-not-taken
(= x __) :another-road-not-taken
:else __)))
"Or your fate may be sealed"
(= 'doom (if-not (zero? __)
'doom
'more-doom))
"In case of emergency, go fast"
(= "pretty fast"
(explain-exercise-velocity __))
"But admit it when you don't know what to do"
(= __
(explain-exercise-velocity :watching-tv)))

35
src/koans/09_higher_order_functions.clj
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@ -1,35 +0,0 @@
(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]))
"You may create that mapping"
(= [1 4 9 16 25] (map (fn [x] __) [1 2 3 4 5]))
"Or use the names of existing functions"
(= __ (map nil? [:a :b nil :c :d]))
"A filter can be strong"
(= __ (filter (fn [x] false) '(:anything :goes :here)))
"Or very weak"
(= __ (filter (fn [x] true) '(:anything :goes :here)))
"Or somewhere in between"
(= [10 20 30] (filter (fn [x] __) [10 20 30 40 50 60 70 80]))
"Maps and filters may be combined"
(= [10 20 30] (map (fn [x] __) (filter (fn [x] __) [1 2 3 4 5 6 7 8])))
"Reducing can increase the result"
(= __ (reduce (fn [a b] (* a b)) [1 2 3 4]))
"You can start somewhere else"
(= 2400 (reduce (fn [a b] (* a b)) __ [1 2 3 4]))
"Numbers are not the only things one can reduce"
(= "longest" (reduce (fn [a b]
(if (< __ __) b a))
["which" "word" "is" "longest"])))

42
src/koans/10_runtime_polymorphism.clj
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@ -1,42 +0,0 @@
(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 ", " (cons a more)))
"!")))
(defmulti diet (fn [x] (:eater x)))
(defmethod diet :herbivore [a] __)
(defmethod diet :carnivore [a] __)
(defmethod diet :default [a] __)
(meditations
"Some functions can be used in different ways - with no arguments"
(= __ (hello))
"With one argument"
(= __ (hello "world"))
"Or with many arguments"
(= __
(hello "Peter" "Paul" "Mary"))
"Multimethods allow more complex dispatching"
(= "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}))
"You may use a default method when no others match"
(= "I don't know what Rich Hickey eats."
(diet {:name "Rich Hickey"})))

28
src/koans/11_lazy_sequences.clj
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@ -1,28 +0,0 @@
(ns koans.11-lazy-sequences
(:require [koan-engine.core :refer :all]))
(meditations
"There are many ways to generate a sequence"
(= __ (range 1 5))
"The range starts at the beginning by default"
(= __ (range 5))
"Only take what you need when the sequence is large"
(= [0 1 2 3 4 5 6 7 8 9]
(take __ (range 100)))
"Or limit results by dropping what you don't need"
(= [95 96 97 98 99]
(drop __ (range 100)))
"Iteration provides an infinite lazy sequence"
(= __ (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 "hello")
(take 100 (iterate ___ "hello"))))

36
src/koans/12_sequence_comprehensions.clj
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@ -1,36 +0,0 @@
(ns koans.12-sequence-comprehensions
(:require [koan-engine.core :refer :all]))
(meditations
"Sequence comprehensions can bind each element in turn to a symbol"
(= __
(for [x (range 6)]
x))
"They can easily emulate mapping"
(= '(0 1 4 9 16 25)
(map (fn [x] (* x x))
(range 6))
(for [x (range 6)]
__))
"And also filtering"
(= '(1 3 5 7 9)
(filter odd? (range 10))
(for [x __ :when (odd? x)]
x))
"Combinations of these transformations are trivial"
(= '(1 9 25 49 81)
(map (fn [x] (* x x))
(filter odd? (range 10)))
(for [x (range 10) :when __]
__))
"More complex transformations simply take multiple binding forms"
(= [[:top :left] [:top :middle] [:top :right]
[:middle :left] [:middle :middle] [:middle :right]
[:bottom :left] [:bottom :middle] [:bottom :right]]
(for [row [:top :middle :bottom]
column [:left :middle :right]]
__)))

35
src/koans/13_creating_functions.clj
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(ns koans.13-creating-functions
(:require [koan-engine.core :refer :all]))
(defn square [x] (* x x))
(meditations
"One may know what they seek by knowing what they do not seek"
(= [__ __ __] (let [not-a-symbol? (complement symbol?)]
(map not-a-symbol? [:a 'b "c"])))
"Praise and 'complement' may help you separate the wheat from the chaff"
(= [:wheat "wheat" 'wheat]
(let [not-nil? ___]
(filter not-nil? [nil :wheat nil "wheat" nil 'wheat nil])))
"Partial functions allow procrastination"
(= 20 (let [multiply-by-5 (partial * 5)]
(___ __)))
"Don't forget: first things first"
(= [__ __ __ __]
(let [ab-adder (partial concat [:a :b])]
(ab-adder [__ __])))
"Functions can join forces as one 'composed' function"
(= 25 (let [inc-and-square (comp square inc)]
(inc-and-square __)))
"Have a go on a double dec-er"
(= __ (let [double-dec (comp dec dec)]
(double-dec 10)))
"Be careful about the order in which you mix your functions"
(= 99 (let [square-and-dec ___]
(square-and-dec 10))))

54
src/koans/14_recursion.clj
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(ns koans.14-recursion
(:require [koan-engine.core :refer :all]))
(defn is-even? [n]
(if (= n 0)
__
(___ (is-even? (dec n)))))
(defn is-even-bigint? [n]
(loop [n n
acc true]
(if (= n 0)
__
(recur (dec n) (not acc)))))
(defn recursive-reverse [coll]
__)
(defn factorial [n]
__)
(meditations
"Recursion ends with a base case"
(= true (is-even? 0))
"And starts by moving toward that base case"
(= false (is-even? 1))
"Having too many stack frames requires explicit tail calls with recur"
(= false (is-even-bigint? 100003N))
"Reversing directions is easy when you have not gone far"
(= '(1) (recursive-reverse [1]))
"Yet it becomes more difficult the more steps you take"
(= '(6 5 4 3 2) (recursive-reverse [2 3 4 5 6]))
"Simple things may appear simple"
(= 1 (factorial 1))
"They may require other simple steps"
(= 2 (factorial 2))
"Sometimes a slightly bigger step is necessary"
(= 6 (factorial 3))
"And eventually you must think harder"
(= 24 (factorial 4))
"You can even deal with very large numbers"
(< 1000000000000000000000000N (factorial 1000N))
"But what happens when the machine limits you?"
(< 1000000000000000000000000N (factorial 100003N)))

44
src/koans/15_destructuring.clj
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(ns koans.15-destructuring
(:require [koan-engine.core :refer :all]))
(def test-address
{:street-address "123 Test Lane"
:city "Testerville"
:state "TX"})
(meditations
"Destructuring is an arbiter: it breaks up arguments"
(= __ ((fn [[a b]] (str b a))
[:foo :bar]))
"Whether in function definitions"
(= (str "An Oxford comma list of apples, "
"oranges, "
"and pears.")
((fn [[a b c]] __)
["apples" "oranges" "pears"]))
"Or in let expressions"
(= "Rich Hickey aka The Clojurer aka Go Time aka Lambda Guru"
(let [[first-name last-name & aliases]
(list "Rich" "Hickey" "The Clojurer" "Go Time" "Lambda Guru")]
__))
"You can regain the full argument if you like arguing"
(= {:original-parts ["Stephen" "Hawking"] :named-parts {:first "Stephen" :last "Hawking"}}
(let [[first-name last-name :as full-name] ["Stephen" "Hawking"]]
__))
"Break up maps by keys"
(= "123 Test Lane, Testerville, TX"
(let [{street-address :street-address, city :city, state :state} test-address]
__))
"Or more succinctly"
(= "123 Test Lane, Testerville, TX"
(let [{:keys [street-address __ __]} test-address]
__))
"All together now!"
(= "Test Testerson, 123 Test Lane, Testerville, TX"
(___ ["Test" "Testerson"] test-address)))

42
src/koans/16_refs.clj
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(ns koans.16-refs
(:require [koan-engine.core :refer :all]))
(def the-world (ref "hello"))
(def bizarro-world (ref {}))
(meditations
"In the beginning, there was a word"
(= __ (deref the-world))
"You can get the word more succinctly, but it's the same"
(= __ @the-world)
"You can be the change you wish to see in the world."
(= __ (do
(dosync (ref-set the-world "better"))
@the-world))
"Alter where you need not replace"
(= __ (let [exclamator (fn [x] (str x "!"))]
(dosync
(alter the-world exclamator)
(alter the-world exclamator)
(alter the-world exclamator))
@the-world))
"Don't forget to do your work in a transaction!"
(= 0 (do __
@the-world))
"Functions passed to alter may depend on the data in the ref"
(= 20 (do
(dosync (alter the-world ___))))
"Two worlds are better than one"
(= ["Real Jerry" "Bizarro Jerry"]
(do
(dosync
(ref-set the-world {})
(alter the-world assoc :jerry "Real Jerry")
(alter bizarro-world assoc :jerry "Bizarro Jerry")
__))))

33
src/koans/17_atoms.clj
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(ns koans.17-atoms
(:require [koan-engine.core :refer :all]))
(def atomic-clock (atom 0))
(meditations
"Atoms are like refs"
(= __ @atomic-clock)
"You can change at the swap meet"
(= __ (do
(swap! atomic-clock inc)
@atomic-clock))
"Keep taxes out of this: swapping requires no transaction"
(= 5 (do
__
@atomic-clock))
"Any number of arguments might happen during a swap"
(= __ (do
(swap! atomic-clock + 1 2 3 4 5)
@atomic-clock))
"Atomic atoms are atomic"
(= __ (do
(compare-and-set! atomic-clock 100 :fin)
@atomic-clock))
"When your expectations are aligned with reality, things proceed that way"
(= :fin (do
(compare-and-set! __ __ __)
@atomic-clock)))

25
src/koans/18_quote.clj
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(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)))

47
src/koans/19_datatypes.clj
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@ -1,47 +0,0 @@
(ns koans.19-datatypes
(:require [koan-engine.core :refer :all]))
(defrecord Nobel [prize])
(deftype Pulitzer [prize])
(defprotocol Award
(present [this recipient]))
(defrecord Oscar [category]
Award
(present [this recipient]
(print (str "Congratulations on your "
(:category this) " Oscar, "
recipient
"!"))))
(deftype Razzie [category]
Award
(present [this recipient]
__))
(meditations
"Holding records is meaningful only when the record is worthy of you"
(= __ (.prize (Nobel. "peace")))
"Types are quite similar"
(= __ (.prize (Pulitzer. "literature")))
"Records may be treated like maps"
(= __ (:prize (Nobel. "physics")))
"While types may not"
(= __ (:prize (Pulitzer. "poetry")))
"Further study reveals why"
(= __
(map map? [(Nobel. "chemistry")
(Pulitzer. "music")]))
"Either sort of datatype can define methods in a protocol"
(= __
(with-out-str (present (Oscar. "Best Picture") "Evil Alien Conquerors")))
"Surely we can implement our own by now"
(= "You're really the Worst Picture, Final Destination 5... sorry."
(with-out-str (present (Razzie. "Worst Picture") "Final Destination 5"))))

19
src/koans/20_java_interop.clj
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(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
"The dot signifies easy and direct Java interoperation"
(= __ (.toUpperCase "select * from"))
"But instance method calls are very different from normal functions"
(= ["SELECT" "FROM" "WHERE"] (map ___ ["select" "from" "where"]))
"Constructing might be harder than breaking"
(= 10 (let [latch (java.util.concurrent.CountDownLatch. __)]
(.getCount latch)))
"Static methods are slashing prices!"
(== __ (Math/pow 2 10)))

21
src/koans/21_partition.clj
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@ -1,21 +0,0 @@
(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)))
"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 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"
(= '((0 1 2) (3 4 5) (6 :hello)) (partition 3 3 [__] (range 7)))
"But notice that they will only pad up to the given sequence length"
(= '((0 1 2) (3 4 5) __) (partition 3 3 [:these :are "my" "words"] (range 7))))

36
src/koans/22_group_by.clj
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(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}])))

51
src/koans/23_meta.clj
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(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))))

45
src/koans/24_macros.clj
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(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-concise [form]
`(~(second form) ; Note the syntax-quote (`) and unquote (~) characters!
__
__))
(defmacro recursive-infix [form]
(cond (not (seq? form))
__
(= 1 (count form))
`(recursive-infix ~(first form))
:else
(let [operator (second form)
first-arg (first form)
others __]
`(~operator
(recursive-infix ~first-arg)
(recursive-infix ~others)))))
(meditations
"Macros are like functions created at compile time"
(= __ (hello "Macros!"))
"I can haz infix?"
(= __ (infix (9 + 1)))
"Remember, these are nothing but code transformations"
(= __ (macroexpand '(infix (9 + 1))))
"You can do better than that - hand crafting FTW!"
(= '(* 10 2) (macroexpand '(infix-concise (10 * 2))))
"Things don't always work as you would like them to"
(= '(+ 10 (2 * 3)) (macroexpand '(infix-concise (10 + (2 * 3)))))
"Really, you don't understand recursion until you understand recursion"
(= 36 (recursive-infix (10 + (2 * 3) + (4 * 5)))))

66
src/koans/25_threading_macros.clj
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(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 []))))

30
src/koans/26_transducers.clj
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(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])))

44
src/koans/27_multimethods.clj
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(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]})))