You have achieved clojure enlightenment. Namaste.

master
J. Fernando Sánchez 6 years ago
parent 809af93e35
commit 8ce6e37c49

@ -3,37 +3,38 @@
(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)
(= nil nil)
"When things cannot be equal, they must be different"
(not= :fill-in-the-blank __))
(not= :fill-in-the-blank "fill in the blank"))

@ -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 occurrence 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? "b"))
"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?")))

@ -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!"))))

@ -3,31 +3,32 @@
(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)))

@ -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})))

@ -3,60 +3,60 @@
(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))
"Create a new map by merging"
(= {:a 1 :b 2 __ __} (merge {:a 1 :b 2} {:c 3}))
(= {:a 1 :b 2 :c 3} (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}))
(= {:a 1 :b 2 :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 __ __ __)
(= (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"})))
"You can even iterate over the map entries as a seq"
(= {:a __ :b __}
(= {:a 2 :b 3}
(into {}
(map
(fn [[k v]] [k (inc v)])

@ -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"
(= __ (#(str "AA" %2) "bb" "CC"))
(= "AACC" (#(str "AA" %2) "bb" "CC"))
"One function can beget another"
(= 9 (((fn [] ___)) 4 5))
(= 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 (___
(= 25 ( #(% 5)
(fn [n] (* n n))))
"But they are often better written using the names of functions"
(= 25 (___ square)))
(= 25 ( #(% 5) square)))

@ -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
(= x __) :another-road-not-taken
:else __)))
(= :your-road (cond (= x 1) :road-not-taken
(= x 2) :another-road-not-taken
:else :your-road)))
"Or your fate may be sealed"
(= 'doom (if-not (zero? __)
(= 'doom (if-not (zero? 10)
'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)))

@ -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 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] (* x 10)) (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"])))

@ -10,19 +10,19 @@
"!")))
(defmulti diet (fn [x] (:eater x)))
(defmethod diet :herbivore [a] __)
(defmethod diet :carnivore [a] __)
(defmethod diet :default [a] __)
(defmethod diet :herbivore [a] (str (:name a) " eats veggies."))
(defmethod diet :carnivore [a] (str (:name a) " eats animals."))
(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"

@ -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 8 (iterate (fn [x] (* x 2)) 1)))
(= '(1 2 4 8 16 32 64 128) (take 8 (iterate (fn [x] (* x 2)) 1)))
"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 #(str %) "hello"))))

@ -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])))

@ -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 :c :d]
(let [ab-adder (partial concat [:a :b])]
(ab-adder [__ __])))
(ab-adder [:c :d])))
"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))))

@ -3,21 +3,28 @@
(defn is-even? [n]
(if (= n 0)
__
(___ (is-even? (dec n)))))
true
(not (is-even? (dec n)))))
(defn is-even-bigint? [n]
(loop [n n
acc true]
(if (= n 0)
__
acc
(recur (dec n) (not acc)))))
(defn recursive-reverse [coll]
__)
(if (empty? coll)
coll
(concat (recursive-reverse (rest coll)) (list (first coll)))))
(defn factorial [n]
__)
(loop [n n
acc 1]
(if (= n 0)
acc
(recur (dec n) (* n acc)))
))
(meditations
"Recursion ends with a base case"

@ -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]))
"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")]
__))
(clojure.string/join " aka " (conj aliases (str first-name " " last-name))))
)
"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"]]
__))
{:original-parts full-name :named-parts {: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]
__))
(str 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]
(str street-address ", " city ", " state)))
"All together now!"
(= "Test Testerson, 123 Test Lane, Testerville, TX"
(___ ["Test" "Testerson"] test-address)))
((fn [[first-name last-name] {:keys [street-address city state]}]
(str first-name " " last-name ", " street-address ", " city ", " state)) ["Test" "Testerson"] test-address)))

@ -6,31 +6,31 @@
(meditations
"In the beginning, there was a word"
(= __ (deref the-world))
(= "hello" (deref the-world))
"You can get the word more succinctly, but it's the same"
(= __ @the-world)
(= "hello" @the-world)
"You can be the change you wish to see in the world."
(= __ (do
(dosync (ref-set the-world "better"))
@the-world))
(= "better" (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))
(= "better!!!" (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 __
(= 0 (do (dosync (ref-set the-world 0))
@the-world))
"Functions passed to alter may depend on the data in the ref"
(= 20 (do
(dosync (alter the-world ___))))
(= 20 (do ()
(dosync (alter the-world + 20))))
"Two worlds are better than one"
(= ["Real Jerry" "Bizarro Jerry"]
@ -39,4 +39,4 @@
(ref-set the-world {})
(alter the-world assoc :jerry "Real Jerry")
(alter bizarro-world assoc :jerry "Bizarro Jerry")
__))))
[(:jerry @the-world) (:jerry @bizarro-world)]))))

@ -5,29 +5,29 @@
(meditations
"Atoms are like refs"
(= __ @atomic-clock)
(= 0 @atomic-clock)
"You can change at the swap meet"
(= __ (do
(= 1 (do
(swap! atomic-clock inc)
@atomic-clock))
"Keep taxes out of this: swapping requires no transaction"
(= 5 (do
__
(swap! atomic-clock + 4)
@atomic-clock))
"Any number of arguments might happen during a swap"
(= __ (do
(= 20 (do
(swap! atomic-clock + 1 2 3 4 5)
@atomic-clock))
"Atomic atoms are atomic"
(= __ (do
(= 20 (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! __ __ __)
(compare-and-set! atomic-clock 20 :fin)
@atomic-clock)))

@ -4,22 +4,22 @@
(meditations
"Wrap a quote around a list to suppress evaluation"
(= (quote (1 2 3 4 5)) __)
(= (quote (1 2 3 4 5)) [ 1 2 3 4 5 ])
"There is a shortcut too!"
(= (quote __) '(1 2 3 4 5))
(= (quote (1 2 3 4 5)) '(1 2 3 4 5))
"You can quote symbols as well as lists... without evaluation!"
(= __ (let [age 9] (quote age)))
(= 'age (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]))
(= (cons 1 (quote (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)))
(= (list 1 (quote (+ 2 3))) '(1 (+ 2 3)))
"Syntax-quote (`) acts similarly to the normal quote"
(= (list __ __ __) `(1 2 3) '(1 2 3))
(= (list 1 2 3) `(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)))
(= (list 1 5) `(1 ~(+ 2 3)) '(1 5)))

@ -18,30 +18,39 @@
(deftype Razzie [category]
Award
(present [this recipient]
__))
(print
(str "You're really the "
(.category this) ", "
recipient
"... sorry.")
)
)
)
(meditations
"Holding records is meaningful only when the record is worthy of you"
(= __ (.prize (Nobel. "peace")))
(= "peace" (.prize (Nobel. "peace")))
"Types are quite similar"
(= __ (.prize (Pulitzer. "literature")))
(= "literature" (.prize (Pulitzer. "literature")))
"Records may be treated like maps"
(= __ (:prize (Nobel. "physics")))
(= "physics" (:prize (Nobel. "physics")))
"While types may not"
(= __ (:prize (Pulitzer. "poetry")))
(= nil (:prize (Pulitzer. "poetry")))
"Further study reveals why"
(= __
(= '(true false)
(map map? [(Nobel. "chemistry")
(Pulitzer. "music")]))
"Either sort of datatype can define methods in a protocol"
(= __
(= "Congratulations on your Best Picture Oscar, Evil Alien Conquerors!"
(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"))))
(with-out-str (present (Razzie. "Worst Picture") "Final Destination 5"))
)
)

@ -3,17 +3,17 @@
(meditations
"You may have done more with Java than you know"
(= __ (class "warfare")) ; hint: try typing (javadoc "warfare") in the REPL
(= String (class "warfare")) ; hint: try typing (javadoc "warfare") in the REPL
"The dot signifies easy and direct Java interoperation"
(= __ (.toUpperCase "select * from"))
(= "SELECT * FROM" (.toUpperCase "select * from"))
"But instance method calls are very different from normal functions"
(= ["SELECT" "FROM" "WHERE"] (map ___ ["select" "from" "where"]))
(= ["SELECT" "FROM" "WHERE"] (map #(.toUpperCase %) ["select" "from" "where"]))
"Constructing might be harder than breaking"
(= 10 (let [latch (java.util.concurrent.CountDownLatch. __)]
(= 10 (let [latch (java.util.concurrent.CountDownLatch. 10)]
(.getCount latch)))
"Static methods are slashing prices!"
(== __ (Math/pow 2 10)))
(== 1024 (Math/pow 2 10)))

@ -3,19 +3,19 @@
(meditations
"To split a collection you can use the partition function"
(= '((0 1) (2 3)) (__ 2 (range 4)))
(= '((0 1) (2 3)) (partition 2 (range 4)))
"But watch out if there are not enough elements to form n sequences"
(= '(__) (partition 3 [:a :b :c :d :e]))
(= '((:a :b :c)) (partition 3 [:a :b :c :d :e]))
"You can use partition-all to include any leftovers too"
(= __ (partition-all 3 (range 5)))
(= '((0 1 2) (3 4)) (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)))
(= '((0 1 2) (5 6 7) (10 11 12)) (partition 3 5 (range 13)))
"Consider padding the last sequence with some default values..."
(= '((0 1 2) (3 4 5) (6 :hello)) (partition 3 3 [__] (range 7)))
(= '((0 1 2) (3 4 5) (6 :hello)) (partition 3 3 [:hello] (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))))
(= '((0 1 2) (3 4 5) (6 :these :are)) (partition 3 3 [:these :are "my" "words"] (range 7))))

@ -2,12 +2,12 @@
(:require [koan-engine.core :refer :all]))
(defn get-odds-and-evens [coll]
(let [{odds true evens false} (group-by __ coll)]
(let [{odds true evens false} (group-by odd? coll)]
[odds evens]))
(meditations
"To categorize a collection by some function, use group-by."
(= __ (group-by count ["hello" "world" "foo" "bar"]))
(= {3 '("foo" "bar") 5 '("hello" "world")} (group-by count ["hello" "world" "foo" "bar"]))
"You can simulate filter + remove in one pass"
(= (get-odds-and-evens [1 2 3 4 5])
@ -15,7 +15,9 @@
[[1 3 5] [2 4]])
"You can also group by a primary key"
(= __
(= {1 '({:id 1 :name "Bob"}
{:id 1 :last-name "Smith"})
2 '({:id 2 :name "Jennifer"})}
(group-by :id [{:id 1 :name "Bob"}
{:id 2 :name "Jennifer"}
{:id 1 :last-name "Smith"} ]))
@ -23,13 +25,13 @@
"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}]}
nil [{: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"
(= __
(= {:naughty-list '({:name "Jimmy" :bad true} {:name "Joe" :bad true}) :nice-list '({:name "Jane" :bad false})}
(group-by #(if (:bad %) :naughty-list :nice-list)
[{:name "Jimmy" :bad true}
{:name "Jane" :bad false}

@ -7,13 +7,13 @@
(meditations
"Some objects can be tagged using the with-meta function"
(= __ (meta giants))
(= {:league "National League"} (meta giants))
"Or more succinctly with a reader macro"
(= __ (meta '^{:division "West"} Giants))
(= {:division "West"} (meta '^{:division "West"} Giants))
"While others can't"
(= __ (try
(= "This doesn't implement the IObj interface" (try
(with-meta
2
{:prime true})
@ -21,31 +21,31 @@
"This doesn't implement the IObj interface")))
"Notice when metadata carries over"
(= __ (meta (merge '^{:foo :bar} {:a 1 :b 2}
(= {:foo :bar } (meta (merge '^{:foo :bar} {:a 1 :b 2}
{:b 3 :c 4})))
"And when it doesn't"
(= __ (meta (merge {:a 1 :b 2}
(= nil (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"))
(= \C (#(.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)) __)
(swap! (:world-series-titles (meta giants)) inc)
@(:world-series-titles (meta giants))))
"You can also create a new object from another object with metadata"
(= {:league "National League" :park "AT&T Park"}
(meta (vary-meta giants
assoc __ __)))
assoc :park "AT&T Park")))
"But it won't affect behavior like equality"
(= __ (vary-meta giants dissoc :league))
(= giants (vary-meta giants dissoc :league))
"Or the object's printed representation"
(= __ (pr-str (vary-meta giants dissoc :league))))
(= "Giants" (pr-str (vary-meta giants dissoc :league))))

@ -9,31 +9,31 @@
(defmacro infix-concise [form]
`(~(second form) ; Note the syntax-quote (`) and unquote (~) characters!
__
__))
~(first form)
~(nth form 2)))
(defmacro recursive-infix [form]
(cond (not (seq? form))
__
form
(= 1 (count form))
`(recursive-infix ~(first form))
:else
(let [operator (second form)
first-arg (first form)
others __]
others (drop 2 form)]
`(~operator
(recursive-infix ~first-arg)
(recursive-infix ~others)))))
(meditations
"Macros are like functions created at compile time"
(= __ (hello "Macros!"))
(= "Hello, Macros!" (hello "Macros!"))
"I can haz infix?"
(= __ (infix (9 + 1)))
(= (+ 9 1) (infix (9 + 1)))
"Remember, these are nothing but code transformations"
(= __ (macroexpand '(infix (9 + 1))))
(= '(+ 9 1) (macroexpand '(infix (9 + 1))))
"You can do better than that - hand crafting FTW!"
(= '(* 10 2) (macroexpand '(infix-concise (10 * 2))))

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