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functiondictionaryvectorclojure

Clojure: Run map on a single value over a list of functions

Say I have 2 functions add1 & sub1, as defined below. From these functions I create a vector funclist.

(defn add1
  [x]
  (+ x 1))

(defn sub1
  [x]
  (- x 1))

(def funclist (vec '(add1 sub1)))

Suppose now on this list of functions, I want to run a map as below

(map #(% 3) funclist)

This gives me

=> (nil nil)

I was expecting (4 2).... What am I doing wrong?

I am a complete Clojure noob... just FYI

-Abe

Solution

  • You turned your functions into symbols w/ the '.

    (map #(type %) funclist) ;; => (clojure.lang.Symbol clojure.lang.Symbol)

    Yet, symbols are functions too. They can be used to look-up like get. Hence the nil results:

    ('inc 42)
; → nil

    Change

    (def funclist (vec '(add1 sub1)))

    to

    (def funclist (vector add1 sub1)) ;; or [add1 sub1]

    And it will work.

    (map #(% 3) funclist) ;;=> (4 2)