36 lines
1.1 KiB
Clojure
36 lines
1.1 KiB
Clojure
(ns koans.08-higher-order-functions
|
|
(:require [koan-engine.core :refer :all]))
|
|
|
|
(meditations
|
|
"The map function relates a sequence to another"
|
|
(= [__ __ __] (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]))
|
|
|
|
"Or use the names of existing functions"
|
|
(= __ (map nil? [:a :b nil :c :d]))
|
|
|
|
"A filter can be strong"
|
|
(= __ (filter (fn [x] false) '(:anything :goes :here)))
|
|
|
|
"Or very weak"
|
|
(= __ (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]))
|
|
|
|
"Maps and filters may be combined"
|
|
(= [10 20 30] (map (fn [x] __) (filter (fn [x] __) [1 2 3 4 5 6 7 8])))
|
|
|
|
"Reducing can increase the result"
|
|
(= __ (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]))
|
|
|
|
"Numbers are not the only things one can reduce"
|
|
(= "longest" (reduce (fn [a b]
|
|
(if (< __ __) b a))
|
|
["which" "word" "is" "longest"])))
|