Clojure Koans Answers and Explanations - 6 - functions

Here is the solution for Clojure Koans on functions.

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;1

; sample functions

(defn multiply-by-ten [n]

  (* 10 n))

(defn square [n] (* n n))

; defn is equivalent of def in Python, Ruby

; is the same as FUNCTION in PL SQL, MYSQL UDF

; is same as subroutine in Perl

; is same as function in Pascal, Fortran, PHP

; there are no close equivalents in C/C++/Java

; is a shorthand of def + fn in Clojure

; In clojure args to function are passed in []

; body is of course defined in ()

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;2

(= __ (multiply-by-ten 2))

; 20

(= 20 (multiply-by-ten 2))

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;3

(= __ ((fn [n] (* __ n)) 2))

; here the function has no name and is anonymous function

(= (multiply-by-ten 2) ((fn [n] (* 10 n)) 2))

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;4

(= __ (#(* 15 %) __))

; there is an alternate syntax

; a kind of shorthand

; the form preferred by experienced Clojurist

(= 30 (#(* 15 %) 2))

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;5

(= __ (#(+ %1 %2 %3) 4 5 6))

; anonymous functions can take arguments as well

; this anonymous function function

; takes 4 5 6 as args and applies + over them

(= 15 (#(+ %1 %2 %3) 4 5 6))

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;6

(= __ ((fn []

           ((fn [a b] (__ a b))

            4 5))))

; this is the practice rather than exception

; in lisp and clojure

(= 20 ((fn []

           ((fn [a b] (* a b))

            4 5))))

; a serious question would have been this.

; removing a set of paren

; stops the anonymous function from executing

(= __ (fn []

           ((fn [a b] (* a b))

            4 5)))

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;7

(= 25 (___

         (fn [n] (* n n))))

; a higher order function taking another function as arg

; here the anonymous function (fn [n] (* n n) needs to be passed to

; another function such that the final result is 25

 (= 25 ((fn [aFun] (aFun 5))

         (fn [n] (* n n))))

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;8

(= 25 (___ square)))

; lets use the square function defined in the beginning

; the function square is passed as an arg to the anonymous function

; which does nothing but invoke the function.

(= 25 ( (fn[aFun](aFun 5)) square))