From cf20fb66e39fab4903c263b3a09c8158015a73b2 Mon Sep 17 00:00:00 2001
From: Colin Jones <trptcolin@gmail.com>
Date: Sun, 7 Feb 2010 22:29:31 -0600
Subject: [PATCH] adding about maps

---
 koans/about_maps.clj            | 48 +++++++++++++++++++++++++++++++++
 koans/path_to_enlightenment.clj |  3 ++-
 2 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 koans/about_maps.clj

diff --git a/koans/about_maps.clj b/koans/about_maps.clj
new file mode 100644
index 0000000..9215453
--- /dev/null
+++ b/koans/about_maps.clj
@@ -0,0 +1,48 @@
+(meditations
+  "Maps in clojure associate keys with values"
+  (= __ (.size (hash-map)))
+
+  "There are two ways to create maps"
+  (= {} (hash-map))
+
+  "A value must be supplied for each key"
+  (= {:a 1} (hash-map :a __))
+
+  "The size is the number of entries"
+  (= __ (.size {: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"
+  (= nil (get {:a 1 :b 2} :c))
+
+  "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 "Febuary"} 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"}))))
+
diff --git a/koans/path_to_enlightenment.clj b/koans/path_to_enlightenment.clj
index e8b9d62..e0934f7 100644
--- a/koans/path_to_enlightenment.clj
+++ b/koans/path_to_enlightenment.clj
@@ -15,4 +15,5 @@
 (load "about_equalities")
 (load "about_vectors")
 (load "about_sets")
-(println "You have acheived clojure enlightenment. Namaste.")
\ No newline at end of file
+(load "about_maps")
+(println "You have acheived clojure enlightenment. Namaste.")