Re-implement Map – Rich 4Clojure Problem 118 – See: https://github.com/PEZ/rich4clojure

rich4clojure_easy_problem_118.clj

(ns rich4clojure.easy.problem-118
  (:require [hyperfiddle.rcf :refer [tests]]))

;; = Re-implement Map =
;; By 4Clojure user: semisight
;; Difficulty: Easy
;; Tags: [core-seqs]
;; 
;; Map is one of the core elements of a functional
;; programming language. Given a function f and an input
;; sequence s, return a lazy sequence of (f x) for each
;; element x in s .

(def restricted [map map-indexed mapcat for])

(def __ :tests-will-fail)

(comment
  
  )

(tests
  [3 4 5 6 7] :=
   (__ inc [2 3 4 5 6])
  (repeat 10 nil) :=
   (__ (fn [_] nil) (range 10))
  [1000000 1000001] :=
   (->> (__ inc (range))
        (drop (dec 1000000))
        (take 2)))

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

;; Post your solution below, please!

(defn select [f s]
  (lazy-seq
   (when-let [[h & t] (seq s)]
     (cons (f h) (select f t)))))