clojure.core/complement

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Type: function Added: Clojure 1.0 Examples: 4 Runnable: 3

([f])

Takes a fn f and returns a fn that takes the same arguments as f, has the same effects, if any, and returns the opposite truth value.

Examples

by mattdw on 2010-07-28 ▶

;; a simple not-empty? predicate (def not-empty? (complement empty?)) ;; #'user/not-empty? (not-empty? []) ;;=> false (not-empty? [1 2]) ;;=> true ;; a slightly more complex example ;; this function takes two arguments, and sometimes returns nil (defn contains-char? [the-string, the-char] (some #(= the-char %) the-string)) ;; #'user/contains-char? (contains-char? "abc" \b) ;;=> true (contains-char? "abc" \j) ;;=> nil ;; define the complement, to check if a char is absent (def does-not-contain-char? (complement contains-char?)) ;; #'user/does-not-contain-char? ;; our complement does exactly what we expect (does-not-contain-char? "abc" \b) ;;=> false (does-not-contain-char? "abc" \j) ;;=> true

by MokkeMeguru on 2017-08-28 . May have evaluation errors. ▶

(map (complement even?) '(1 2 3 4)) ;; return... ;; (true false true false) ;; see also ... (map even? '(1 2 3 4)) ;; (false true false true) ;; WARNING ;; This function returns ERROR!!! (map (not even?) '(1 2 3 4)) (map #(not (even? %)) '(1 2 3 4)) ; This works

by ibercode on 2018-02-16 ▶

(def not-empty? (complement empty?)) (not-empty? "abcde") ;;true (not-empty? "") ;;false

by wplj on 2020-03-01 ▶

;; flatten function from Clojure core: (defn flatten "Takes any nested combination of sequential things (lists, vectors, etc.) and returns their contents as a single, flat lazy sequence. (flatten nil) returns an empty sequence." {:added "1.2" :static true} [x] (filter (complement sequential?) (rest (tree-seq sequential? seq x))))

See also

• clojure.core/not (2)

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