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Solve higher order functions

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This commit is contained in:
Kenneth Kostresevic 2021-12-15 14:45:14 +01:00
parent a9c22921a5
commit 217b0ace56
1 changed files with 10 additions and 10 deletions
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20
src/koans/09_higher_order_functions.clj
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@ -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 30)) [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 3)) [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"])))