Simple solutions to clojure koans

src/koans/01_equalities.clj

@@ -1,21 +1,21 @@
 (meditations
   "We shall contemplate truth by testing reality, via equality"
-  (= __ true)
+  (= true true)
 
   "To understand reality, we must compare our expectations against reality"
-  (= __ (+ 1 1))
+  (= 2 (+ 1 1))
 
   "You can test equality of many things"
-  (= (+ 3 4) __ (+ 2 __))
+  (= (+ 3 4) 7 (+ 2 5))
 
   "Some things may appear different, but be the same"
-  (= 2 2/1 __)
+  (= 2 2/1 4/2)
 
   "You cannot generally float to heavens of integers"
-  (= __ (= 2 2.0))
+  (= false (= 2 2.0))
 
   "But a looser equality is also possible"
-  (== 2.0 2 __)
+  (== 2.0 2 4/2)
 
   "When things cannot be equal, they must be different"
-  (not= :fill-in-the-blank __))
+  (not= :fill-in-the-blank :not))

src/koans/02_lists.clj

@@ -1,34 +1,34 @@
 (meditations
   "Lists can be expressed by function or a quoted form"
-  (= '(__ __ __ __ __) (list 1 2 3 4 5))
+  (= '(1 2 3 4 5) (list 1 2 3 4 5))
 
   "They are Clojure seqs (sequences), so they allow access to the first"
-  (= __ (first '(1 2 3 4 5)))
+  (= 1 (first '(1 2 3 4 5)))
 
   "As well as the rest"
-  (= __ (rest '(1 2 3 4 5)))
+  (= [2 3 4 5] (rest '(1 2 3 4 5)))
 
   "The rest when nothing is left is empty"
-  (= __ (rest '(100)))
+  (= [] (rest '(100)))
 
   "And construction by adding an element to the front is simple"
-  (= __ (cons :a '(:b :c :d :e)))
+  (= '(:a :b :c :d :e) (cons :a '(:b :c :d :e)))
 
   "Conjoining an element to a list can be done in the reverse order"
-  (= __ (conj '(:a :b :c :d :e) 0))
+  (= '(0 :a :b :c :d :e) (conj '(:a :b :c :d :e) 0))
 
   "You can use a list like a stack to get the first element"
-  (= __ (peek '(:a :b :c :d :e)))
+  (= :a (peek '(:a :b :c :d :e)))
 
   "Or the others"
-  (= __ (pop '(:a :b :c :d :e)))
+  (= '(:b :c :d :e) (pop '(:a :b :c :d :e)))
 
   "But watch out if you try to pop nothing"
-  (= __ (try
+  (= "No dice!" (try
           (pop '())
           (catch IllegalStateException e "No dice!")))
 
   "The rest of nothing isn't so strict"
-  (= __ (try
+  (= () (try
           (rest '())
           (catch IllegalStateException e "No dice!"))))

src/koans/03_vectors.clj

@@ -1,33 +1,33 @@
 (meditations
   "You can use vectors in clojure to create an 'Array' like structure"
-  (= __ (count [42]))
+  (= 1 (count [42]))
 
   "You can create a vector in several ways"
-  (= __ (vec nil))
+  (= [] (vec nil))
 
   "And populate it in either of these ways"
-  (= __ (vec '(1)))
+  (= [1]  (vec '(1)))
 
   "There is another way as well"
-  (= __ (vector nil))
+  (= [nil] (vector nil))
 
   "But you can populate it with any number of elements at once"
-  (= [1 __] (vec '(1 2)))
+  (= [1 2] (vec '(1 2)))
 
   "And add to it as well"
-  (= __ (conj (vec nil) 333))
+  (= [333] (conj (vec nil) 333))
 
   "You can get the first element of a vector like so"
-  (= __ (first [:peanut :butter :and :jelly]))
+  (= :peanut (first [:peanut :butter :and :jelly]))
 
   "And the last in a similar fashion"
-  (= __ (last [:peanut :butter :and :jelly]))
+  (= :jelly (last [:peanut :butter :and :jelly]))
 
   "Or any index if you wish"
-  (= __ (nth [:peanut :butter :and :jelly] 3))
+  (= :jelly (nth [:peanut :butter :and :jelly] 3))
 
   "You can also slice a vector"
-  (= __ (subvec [:peanut :butter :and :jelly] 1 3))
+  (= [:butter :and] (subvec [:peanut :butter :and :jelly] 1 3))
 
   "Equality with collections is in terms of values"
-  (= (list 1 2 3) (vector 1 2 __)))
+  (= (list 1 2 3) (vector 1 2 3)))

src/koans/04_sets.clj

@@ -1,18 +1,18 @@
 (meditations
   "You can create a set in two ways"
-  (= #{} (set __))
+  (= #{} (set nil))
 
   "They are another important data structure in clojure"
-  (= __ (count #{1 2 3}))
+  (= 3 (count #{1 2 3}))
 
   "Remember that a set is a 'set'"
-  (= __ (set '(1 1 2 2 3 3 4 4 5 5)))
+  (= #{1 2 3 4 5} (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}))
+  (= #{1 2 3 4 5} (clojure.set/union #{1 2 3 4} #{2 3 5}))
 
   "And also the intersection"
-  (= __ (clojure.set/intersection #{1 2 3 4} #{2 3 5}))
+  (= #{2 3} (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})))
+  (= #{1 4} (clojure.set/difference #{1 2 3 4 5} #{2 3 5})))

src/koans/05_maps.clj

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

src/koans/06_functions.clj

@@ -5,25 +5,25 @@
 
 (meditations
   "Functions are often defined before they are used"
-  (= __ (multiply-by-ten 2))
+  (= 20 (multiply-by-ten 2))
 
   "But they can also be defined inline"
-  (= __ ((fn [n] (* __ n)) 2))
+  (= 20 ((fn [n] (* 10 n)) 2))
 
   "Or using even shorter syntax"
-  (= __ (#(* 15 %) __))
+  (= 20 (#(* 10 %) 2))
 
   "Short anonymous functions may take multiple arguments"
-  (= __ (#(+ %1 %2 %3) 4 5 6))
+  (= 15 (#(+ %1 %2 %3) 4 5 6))
 
   "One function can beget another"
-  (= __ ((fn []
+  (= 9 ((fn []
-           ((fn [a b] (__ a b))
+           ((fn [a b] (+ a b))
             4 5))))
 
   "Higher-order functions take function arguments"
-  (= 25 (___
+  (= 25 ((fn [func] (func 5))
          (fn [n] (* n n))))
 
   "But they are often better written using the names of functions"
-  (= 25 (___ square)))
+  (= 25 ((defn square5 [square] (square 5)) square)))

src/koans/07_conditionals.clj

@@ -9,38 +9,38 @@
 
 (meditations
   "You will face many decisions"
-  (= __ (if (false? (= 4 5))
+  (= :a (if (false? (= 4 5))
           :a
           :b))
 
   "Some of them leave you no alternative"
-  (= __ (if (> 4 3)
+  (= [] (if (> 4 3)
           []))
 
   "And in such a situation you may have nothing"
-  (= __ (if (nil? 0)
+  (= nil (if (nil? 0)
           [:a :b :c]))
 
   "In others your alternative may be interesting"
   (= :glory (if (not (empty? ()))
               :doom
-              __))
+              :glory))
 
   "You may have a multitude of possible paths"
   (let [x 5]
-    (= :your-road (cond (= x __) :road-not-taken
+    (= :your-road (cond (= x 2) :road-not-taken
-                        (= x __) :another-road-not-taken
+                        (= x 3) :another-road-not-taken
-                        :else __)))
+                        :else :your-road)))
 
   "Or your fate may be sealed"
-  (= __ (if-not (zero? __)
+  (= 'doom (if-not (zero? 1)
           'doom
           'doom))
 
   "In case of emergency, sound the alarms"
   (= :sirens
-     (explain-defcon-level __))
+     (explain-defcon-level :cocked-pistol))
 
   "But admit it when you don't know what to do"
-  (= __
+  (= :say-what?
      (explain-defcon-level :yo-mama)))

src/koans/08_higher_order_functions.clj

@@ -1,32 +1,32 @@
 (meditations
   "The map function relates a sequence to another"
-  (= [__ __ __] (map (fn [x] (* 4 x)) [1 2 3]))
+  (= [4 8 12] (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]))
+  (= [1 4 9 16 25] (map (fn [x] (* x x)) [1 2 3 4 5]))
 
   "Or use the names of existing functions"
-  (= __ (map nil? [:a :b nil :c :d]))
+  (= [false false true false false] (map nil? [:a :b nil :c :d]))
 
   "A filter can be strong"
-  (= __ (filter (fn [x] false) '(:anything :goes :here)))
+  (= [] (filter (fn [x] false) '(:anything :goes :here)))
 
   "Or very weak"
-  (= __ (filter (fn [x] true) '(:anything :goes :here)))
+  (= [:anything :goes :here] (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]))
+  (= [10 20 30] (filter (fn [x] (< x 40)) [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])))
+  (= [10 20 30] (map (fn [x] (* 10 x)) (filter (fn [x] (< x 4)) [1 2 3 4 5 6 7 8])))
 
   "Reducing can increase the result"
-  (= __ (reduce (fn [a b] (* a b)) [1 2 3 4]))
+  (= 24 (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]))
+  (= 2400 (reduce (fn [a b] (* a b)) 100 [1 2 3 4]))
 
   "Numbers are not the only things one can reduce"
   (= "longest" (reduce (fn [a b]
-                         (if (< __ __) b a))
+                         (if (< (count a) (count b)) b a))
                        ["which" "word" "is" "longest"])))