Merge db99c57eb1 into b31227c0a8

src/koans/01_equalities.clj

@@ -3,37 +3,37 @@
 
 (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) 7 (+ 2 __))
+  (= (+ 3 4) 7 (+ 2 5))
 
   "Some things may appear different, but be the same"
-  (= __ (= 2 2/1))
+  (= true (= 2 2/1))
 
   "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))
+  (= true (== 2.0 2))
 
   "Something is not equal to nothing"
-  (= __ (not (= 1 nil)))
+  (= true (not (= 1 nil)))
 
   "Strings, and keywords, and symbols: oh my!"
-  (= __ (= "hello" :hello 'hello))
+  (= false (= "hello" :hello 'hello))
 
   "Make a keyword with your keyboard"
-  (= :hello (keyword __))
+  (= :hello (keyword "hello"))
 
   "Symbolism is all around us"
-  (= 'hello (symbol __))
+  (= 'hello (symbol "hello"))
 
   "What could be equivalent to nothing?"
   (= __ nil)
 
   "When things cannot be equal, they must be different"
-  (not= :fill-in-the-blank __))
+  (not= :fill-in-the-blank :not-equal))

src/koans/02_strings.clj

@@ -4,67 +4,67 @@
 
 (meditations
   "A string is nothing more than text surrounded by double quotes"
-  (= __ "hello")
+  (= "hello" "hello")
 
   "But double quotes are just magic on top of something deeper"
-  (= __ (str 'world))
+  (= "world" (str 'world))
 
   "You can do more than create strings, you can put them together"
-  (= "Cool right?" (str __ __))
+  (= "Cool right?" (str "Cool right?"))
 
   "You can even get certain characters"
-  (= \C (get "Characters" __))
+  (= \C (get "Characters" 0))
 
   "Or even count the characters"
-  (= __ (count "Hello World"))
+  (= 11 (count "Hello World"))
 
   "But strings and characters are not the same"
-  (= __ (= \c "c"))
+  (= false (= \c "c"))
 
   "What if you only wanted to get part of a string?"
-  (= "World" (subs "Hello World" __ __))
+  (= "World" (subs "Hello World" 6 11))
 
   "How about joining together elements in a list?"
-  (= __ (string/join '(1 2 3)))
+  (= "123" (string/join '(1 2 3)))
 
   "What if you wanted to separate them out?"
-  (= "1, 2, 3" (string/join __ '(1 2 3)))
+  (= "1, 2, 3" (string/join ", " '(1 2 3)))
 
   "Maybe you want to separate out all your lines"
-  (= [__ __ __] (string/split-lines "1\n2\n3"))
+  (= ["1", "2", "3"] (string/split-lines "1\n2\n3"))
 
   "You may want to make sure your words are backwards"
-  (= __ (string/reverse "hello"))
+  (= "olleh" (string/reverse "hello"))
 
   "Maybe you want to find the index of the first occurence of a substring"
-  (= 0 (string/index-of "hello world" __))
+  (= 0 (string/index-of "hello world" "h"))
 
   "Or maybe the last index of the same"
-  (= __ (string/last-index-of "hello world, hello" "hello"))
+  (= 13 (string/last-index-of "hello world, hello" "hello"))
 
   "But when something doesn't exist, nothing is found"
-  (= __ (string/index-of "hello world" "bob"))
+  (= nil (string/index-of "hello world" "bob"))
 
   "Sometimes you don't want whitespace cluttering the front and back"
-  (= __ (string/trim "  \nhello world \t \n"))
+  (= "hello world" (string/trim "  \nhello world \t \n"))
 
   "You can check if something is a char"
-  (= __ (char? \c))
+  (= true (char? \c))
 
   "But it may not be"
-  (= __ (char? "a"))
+  (= false (char? "a"))
 
   "But chars aren't strings"
-  (= __ (string? \b))
+  (= false (string? \b))
 
   "Strings are strings"
-  (= true (string? __))
+  (= true (string? "string"))
 
   "Some strings may be blank"
-  (= __ (string/blank? ""))
+  (= true (string/blank? ""))
 
   "Even if at first glance they aren't"
-  (= __ (string/blank? " \n \t  "))
+  (= true (string/blank? " \n \t  "))
 
   "However, most strings aren't blank"
-  (= __ (string/blank? "hello?\nare you out there?")))
+  (= false (string/blank? "hello?\nare you out there?")))

src/koans/03_lists.clj

@@ -3,43 +3,43 @@
 
 (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)))
 
   "Count your blessings"
-  (= __ (count '(dracula dooku chocula)))
+  (= 3 (count '(dracula dooku chocula)))
 
   "Before they are gone"
-  (= __ (count '()))
+  (= 0 (count '()))
 
   "The rest, when nothing is left, is empty"
-  (= __ (rest '(100)))
+  (= () (rest '(100)))
 
   "Construction by adding an element to the front is easy"
-  (= __ (cons :a '(:b :c :d :e)))
+  (= '(:a :b :c :d :e) (cons :a '(:b :c :d :e)))
 
   "Conjoining an element to a list isn't hard either"
-  (= __ (conj '(:a :b :c :d) :e))
+  (= '(:e :a :b :c :d) (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)))
+  (= :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/04_vectors.clj

@@ -3,31 +3,31 @@
 
 (meditations
   "You can use vectors in clojure as array-like structures"
-  (= __ (count [42]))
+  (= 1 (count [42]))
 
   "You can create a vector from a list"
-  (= __ (vec '(1)))
+  (= [1] (vec '(1)))
 
   "Or from some elements"
-  (= __ (vector nil nil))
+  (= [nil, nil] (vector nil nil))
 
   "But you can populate it with any number of elements at once"
-  (= [1 __] (vec '(1 2)))
+  (= [1, 2] (vec '(1 2)))
 
   "Conjoining to a vector is different than to a list"
-  (= __ (conj [111 222] 333))
+  (= [111, 222, 333] (conj [111 222] 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/05_sets.clj

@@ -4,19 +4,19 @@
 
 (meditations
   "You can create a set by converting another collection"
-  (= #{3} (set __))
+  (= #{3} (set #{3}))
 
   "Counting them is like counting other collections"
-  (= __ (count #{1 2 3}))
+  (= 3 (count #{1 2 3}))
 
   "Remember that a set is a *mathematical* 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"
-  (= __ (set/union #{1 2 3 4} #{2 3 5}))
+  (= #{1 2 3 4 5} (set/union #{1 2 3 4} #{2 3 5}))
 
   "And also the intersection"
-  (= __ (set/intersection #{1 2 3 4} #{2 3 5}))
+  (= #{2, 3} (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})))
+  (= #{1 4} (set/difference #{1 2 3 4 5} #{2 3 5})))

src/koans/06_maps.clj

@@ -3,48 +3,48 @@
 
 (meditations
   "Don't get lost when creating a map"
-  (= {:a 1 :b 2} (hash-map :a 1 __ __))
+  (= {:a 1 :b 2} (hash-map :a 1 :b 2))
 
   "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 functions to do lookups"
-  (= __ ({: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"
-  (= __ ({2010 "Vancouver" 2014 "Sochi" 2018 "PyeongChang"} 2014))
+  (= "Sochi" ({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))
+  (= 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 and improved version"
-  (= {1 "January" 2 __} (assoc {1 "January"} 2 "February"))
+  (= {1 "January" 2 "February"} (assoc {1 "January"} 2 "February"))
 
   "You can also create a new version with an entry removed"
-  (= {__ __} (dissoc {1 "January" 2 "February"} 2))
+  (= {1 "January"} (dissoc {1 "January" 2 "February"} 2))
 
   "Often you will need to get the keys, but the order is undependable"
-  (= (list __ __ __)
+  (= (list 2010 2014 2018)
      (sort (keys { 2014 "Sochi" 2018 "PyeongChang" 2010 "Vancouver"})))
 
   "You can get the values in a similar way"
-  (= (list __ __ __)
+  (= (list "PyeongChang" "Sochi" "Vancouver")
      (sort (vals {2010 "Vancouver" 2014 "Sochi" 2018 "PyeongChang"}))))

src/koans/07_functions.clj

@@ -8,33 +8,33 @@
 
 (meditations
   "Calling a function is like giving it a hug with parentheses"
-  (= __ (square 9))
+  (= 81 (square 9))
 
   "Functions are usually defined before they are used"
-  (= __ (multiply-by-ten 2))
+  (= 20 (multiply-by-ten 2))
 
   "But they can also be defined inline"
-  (= __ ((fn [n] (* 5 n)) 2))
+  (= 10 ((fn [n] (* 5 n)) 2))
 
   "Or using an even shorter syntax"
-  (= __ (#(* 15 %) 4))
+  (= 60 (#(* 15 %) 4))
 
   "Even anonymous functions may take multiple arguments"
-  (= __ (#(+ %1 %2 %3) 4 5 6))
+  (= 15 (#(+ %1 %2 %3) 4 5 6))
 
   "Arguments can also be skipped"
-  (= __ (#(* 15 %2) 1 2))
+  (= 30 (#(* 15 %2) 1 2))
 
   "One function can beget another"
-  (= 9 (((fn [] ___)) 4 5))
+  (= 9 ((#(fn [a b] (+ a b))) 4 5))
 
   "Functions can also take other functions as input"
   (= 20 ((fn [f] (f 4 5))
-           ___))
+           *))
 
   "Higher-order functions take function arguments"
-  (= 25 (___
+  (= 25 ((fn [aFun] (aFun 5))
           (fn [n] (* n n))))
 
   "But they are often better written using the names of functions"
-  (= 25 (___ square)))
+  (= 25 ((fn [squre] (squre 5)) square)))

src/koans/08_conditionals.clj

@@ -10,38 +10,38 @@
 
 (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 3) :road-not-taken
-                        (= x __) :another-road-not-taken
+                        (= x 2) :another-road-not-taken
-                        :else __)))
+                        :else :your-road)))
 
   "Or your fate may be sealed"
-  (= 'doom (if-not (zero? __)
+  (= 'doom (if-not (zero? 1)
           'doom
           'more-doom))
 
   "In case of emergency, go fast"
   (= "pretty fast"
-     (explain-exercise-velocity __))
+     (explain-exercise-velocity :bicycling))
 
   "But admit it when you don't know what to do"
-  (= __
+  (= "is that even exercise?"
      (explain-exercise-velocity :watching-tv)))

src/koans/09_higher_order_functions.clj

@@ -3,33 +3,33 @@
 
 (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 31)) [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"])))

src/koans/10_runtime_polymorphism.clj

@@ -10,19 +10,19 @@
                    "!")))
 
 (defmulti diet (fn [x] (:eater x)))
-(defmethod diet :herbivore [a] __)
+(defmethod diet :herbivore [a] (str (:name a) " eats veggies."))
-(defmethod diet :carnivore [a] __)
+(defmethod diet :carnivore [a] (str (:name a) " eats animals."))
-(defmethod diet :default [a] __)
+(defmethod diet :default [a] (str "I don't know what " (:name a) " eats."))
 
 (meditations
   "Some functions can be used in different ways - with no arguments"
-  (= __ (hello))
+  (= "Hello World!" (hello))
 
   "With one argument"
-  (= __ (hello "world"))
+  (= "Hello, you silly world." (hello "world"))
 
   "Or with many arguments"
-  (= __
+  (= "Hello to this group: Peter, Paul, Mary!"
      (hello "Peter" "Paul" "Mary"))
 
   "Multimethods allow more complex dispatching"

src/koans/11_lazy_sequences.clj

@@ -3,26 +3,26 @@
 
 (meditations
   "There are many ways to generate a sequence"
-  (= __ (range 1 5))
+  (= '(1 2 3 4) (range 1 5))
 
   "The range starts at the beginning by default"
-  (= __ (range 5))
+  (= '(0 1 2 3 4) (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)))
+     (take 10 (range 100)))
 
   "Or limit results by dropping what you don't need"
   (= [95 96 97 98 99]
-     (drop __ (range 100)))
+     (drop 95 (range 100)))
 
   "Iteration provides an infinite lazy sequence"
-  (= __ (take 20 (iterate inc 0)))
+  (= '(0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19) (take 20 (iterate inc 0)))
 
   "Repetition is key"
   (= [:a :a :a :a :a :a :a :a :a :a]
-     (repeat 10 __))
+     (repeat 10 :a))
 
   "Iteration can be used for repetition"
   (= (repeat 100 :hello)
-     (take 100 (iterate ___ :hello))))
+     (take 100 (iterate identity :hello))))

src/koans/12_sequence_comprehensions.clj

@@ -3,7 +3,7 @@
 
 (meditations
   "Sequence comprehensions can bind each element in turn to a symbol"
-  (= __
+  (= [0 1 2 3 4 5]
      (for [x (range 6)]
        x))
 
@@ -12,20 +12,20 @@
      (map (fn [x] (* x x))
           (range 6))
      (for [x (range 6)]
-       __))
+       (* x x)))
 
   "And also filtering"
   (= '(1 3 5 7 9)
      (filter odd? (range 10))
-     (for [x __ :when (odd? x)]
+     (for [x (range 10) :when (odd? x)]
        x))
 
   "Combinations of these transformations is trivial"
   (= '(1 9 25 49 81)
      (map (fn [x] (* x x))
           (filter odd? (range 10)))
-     (for [x (range 10) :when __]
+     (for [x (range 10) :when (odd? x)]
-       __))
+       (* x x)))
 
   "More complex transformations simply take multiple binding forms"
   (= [[:top :left] [:top :middle] [:top :right]
@@ -33,4 +33,4 @@
       [:bottom :left] [:bottom :middle] [:bottom :right]]
      (for [row [:top :middle :bottom]
            column [:left :middle :right]]
-       __)))
+       [row column])))

src/koans/13_creating_functions.clj

@@ -5,31 +5,31 @@
 
 (meditations
   "One may know what they seek by knowing what they do not seek"
-  (= [__ __ __] (let [not-a-symbol? (complement symbol?)]
+  (= [true false true] (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? ___]
+       (let [not-nil? (complement nil?)]
          (filter not-nil? [nil :wheat nil "wheat" nil 'wheat nil])))
 
   "Partial functions allow procrastination"
   (= 20 (let [multiply-by-5 (partial * 5)]
-          (___ __)))
+          (multiply-by-5 4)))
 
   "Don't forget: first things first"
-  (= [__ __ __ __]
+  (= [:a :b 1 2]
        (let [ab-adder (partial concat [:a :b])]
-         (ab-adder [__ __])))
+         (ab-adder [1 2])))
 
   "Functions can join forces as one 'composed' function"
   (= 25 (let [inc-and-square (comp square inc)]
-          (inc-and-square __)))
+          (inc-and-square 4)))
 
   "Have a go on a double dec-er"
-  (= __ (let [double-dec (comp dec dec)]
+  (= 8 (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 ___]
+  (= 99 (let [square-and-dec (comp dec square)]
           (square-and-dec 10))))

src/koans/14_recursion.clj

@@ -3,21 +3,29 @@
 
 (defn is-even? [n]
   (if (= n 0)
-    __
+    true
-    (___ (is-even? (dec n)))))
+    (not (is-even? (dec n)))))
 
 (defn is-even-bigint? [n]
   (loop [n   n
          acc true]
     (if (= n 0)
-      __
+      false
       (recur (dec n) (not acc)))))
 
 (defn recursive-reverse [coll]
-  __)
+  (loop [coll coll
+          reversed '()]
+         (if (empty? coll)
+           reversed
+           (recur (rest coll) (cons (first coll) reversed)))))
 
 (defn factorial [n]
-  __)
+  (loop [n n
+         res 1]
+    (if (= 0 n)
+      res
+      (recur (dec n) (* n res)))))
 
 (meditations
   "Recursion ends with a base case"

src/koans/15_destructuring.clj

@@ -8,37 +8,39 @@
 
 (meditations
   "Destructuring is an arbiter: it breaks up arguments"
-  (= __ ((fn [[a b]] (str b a))
+  (= ":bar:foo" ((fn [[a b]] (str b a))[:foo :bar]))
-         [:foo :bar]))
 
   "Whether in function definitions"
   (= (str "An Oxford comma list of apples, "
           "oranges, "
           "and pears.")
-     ((fn [[a b c]] __)
+     ((fn [[a b c]] (str "An Oxford comma list of " a ", " b ", and " 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")]
-       __))
+       (apply str (interpose " aka " (cons (str first-name " " last-name) aliases)))))
 
   "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"]]
-       __))
+       (hash-map :original-parts full-name :named-parts (hash-map :first first-name :last last-name))))
 
   "Break up maps by key"
   (= "123 Test Lane, Testerville, TX"
      (let [{street-address :street-address, city :city, state :state} test-address]
-       __))
+       (apply str (interpose ", " (list street-address city state)))))
 
   "Or more succinctly"
   (= "123 Test Lane, Testerville, TX"
-     (let [{:keys [street-address __ __]} test-address]
+     (let [{:keys [street-address city state]} test-address]
-       __))
+       (apply str (interpose ", " (list street-address city state)))))
 
   "All together now!"
   (= "Test Testerson, 123 Test Lane, Testerville, TX"
-     (___ ["Test" "Testerson"] test-address)))
+     ((fn [[a b] {:keys [street-address city state]}]
+        (apply str (interpose ", " (list (str a " " b) street-address city state))))
+
+      ["Test" "Testerson"] test-address))