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# brandon-atkinson's solution

## to Accumulate in the Clojure Track

Published at Jan 18 2021 · 0 comments
Instructions
Test suite
Solution

Implement the `accumulate` operation, which, given a collection and an operation to perform on each element of the collection, returns a new collection containing the result of applying that operation to each element of the input collection.

Given the collection of numbers:

• 1, 2, 3, 4, 5

And the operation:

• square a number (`x => x * x`)

Your code should be able to produce the collection of squares:

• 1, 4, 9, 16, 25

Check out the test suite to see the expected function signature.

## Restrictions

Keep your hands off that collect/map/fmap/whatchamacallit functionality provided by your standard library! Solve this one yourself using other basic tools instead.

## Source

Conversation with James Edward Gray II https://twitter.com/jeg2

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### accumulate_test.clj

``````(ns accumulate-test
(:require [clojure.test :refer [deftest is]]
accumulate))

(defn- square [n] (* n n))

(defn- to-s [xs] (apply str xs))

(deftest empty-accumulation
(is (= [] (accumulate/accumulate square []))))

(deftest accumulate-squares
(is (= [1 4 9] (accumulate/accumulate square [1 2 3]))))

(deftest accumulate-upcases
(is (= ["HELLO", "WORLD"]
(->> ["hello" "world"]
(accumulate/accumulate clojure.string/upper-case)
(map to-s)))))

(deftest accumulate-reversed-strings
(is (= ["eht" "kciuq" "nworb" "xof" "cte"]
(->> ["the" "quick" "brown" "fox" "etc"]
(accumulate/accumulate reverse)
(map to-s)))))

(deftest accumulate-recursively
(is (= [["a1" "a2" "a3"] ["b1" "b2" "b3"] ["c1" "c2" "c3"]]
(-> #(accumulate/accumulate (fn [n] (str % n)) [1 2 3])
(accumulate/accumulate "abc")))))``````
``````(ns accumulate)

(defn accumulate
[fn coll]
(if (empty? coll)
'()
(lazy-seq
(cons (fn (first coll))
(accumulate fn (rest coll))))))``````

### What can you learn from this solution?

A huge amount can be learned from reading other peopleâ€™s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

• What compromises have been made?
• Are there new concepts here that you could read more about to improve your understanding?