Clojure Koans Answers and Explanations - 10 - Lazy Sequences

Let's look at the solutions for the next of Clojure Koans -Lazy Sequences.

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;1

(= __ (range 1 5))

; range is exclusive at the end meaning it is (]

(= '(1 2 3 4) (range 1 5))

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;2

(= [0 1 2 3 4 5 6 7 8 9]

     (take __ (range 100)))

; range produces a lazy seq

; we need to 'take' 10 elements

; so

(= [0 1 2 3 4 5 6 7 8 9]

     (take 10 (range 100)))

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;3

(= [95 96 97 98 99]

     (drop __ (range 100)))

; drop is sound alternative to take

(= [95 96 97 98 99]

     (drop 95 (range 100)))

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;4

(= __ (take 20 (iterate inc 0)))

; iterate is another function producing lazy

; sequence

(= '(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)))

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;5

(= [:a :a :a :a :a :a :a :a :a :a ]

     (repeat 10 __))

; repeat is another lazy sequence

(= [:a :a :a :a :a :a :a :a :a :a ]

     (repeat 10 :a))

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;6

(= (repeat 100 :foo)

     (take 100 (iterate ___ :foo))))

; time for resolving identity crisis

(= (repeat 100 :foo)

     (take 100 (iterate identity :foo)))