Interpose a Seq – Rich 4Clojure Problem 40 – See: https://github.com/PEZ/rich4clojure

rich4clojure_easy_problem_040.clj

(ns rich4clojure.easy.problem-040
  (:require [hyperfiddle.rcf :refer [tests]]))

;; = Interpose a Seq =
;; By 4Clojure user: dbyrne
;; Difficulty: Easy
;; Tags: [seqs core-functions]
;; 
;; Write a function which separates the items of a
;; sequence by an arbitrary value.

(def restricted [interpose])

(def __ :tests-will-fail)

(comment
  
  )

(tests
  (__ 0 [1 2 3]) := [1 0 2 0 3]
  (apply str (__ ", " ["one" "two" "three"])) := "one, two, three"
  (__ :z [:a :b :c :d]) := [:a :z :b :z :c :z :d])

;; To participate, fork:
;; https://github.com/PEZ/rich4clojure

;; Post your solution below, please!

(def __ #(butlast (mapcat list %2 (repeat %))))

(def __ (fn [sep l]
            (butlast (mapcat #(vector %1 sep) l))))

(defn __ [item coll]
  (butlast (interleave coll (repeat item))))

(defn my-interpose
  [v [fst & rst]]
  (lazy-seq
   (if rst
     (cons fst (cons v (my-interpose v rst)))
     (list fst))))

(def __ my-interpose)

(fn [inter-val seq1]
(take
(dec (* 2 (count seq1)))
(mapcat list
seq1
(repeat (count seq1) inter-val)))) ; I didnt know about butlast

  (defn __ [val my-list]
    (drop-last (mapcat #(concat  [%] [val]) my-list)))