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:
And the operation:
x => x * x)
Your code should be able to produce the collection of squares:
Check out the test suite to see the expected function signature.
Keep your hands off that collect/map/fmap/whatchamacallit functionality provided by your standard library! Solve this one yourself using other basic tools instead.
Execute the tests with:
$ mix test
In the test suites, all but the first test have been skipped.
Once you get a test passing, you can unskip the next one by
commenting out the relevant
@tag :pending with a
# @tag :pending test "shouting" do assert Bob.hey("WATCH OUT!") == "Whoa, chill out!" end
Or, you can enable all the tests by commenting out the
ExUnit.configure line in the test suite.
# ExUnit.configure exclude: :pending, trace: true
If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.
Conversation with James Edward Gray II https://twitter.com/jeg2
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
defmodule AccumulateTest do use ExUnit.Case test "accumulate empty list" do assert Accumulate.accumulate(, fn n -> n * n end) ==  end @tag :pending test "accumulate square numbers" do assert Accumulate.accumulate([1, 2, 3], fn n -> n * n end) == [1, 4, 9] end @tag :pending test "accumulate upcased strings" do fun = fn w -> String.upcase(w) end assert Accumulate.accumulate(["hello", "world"], fun) == ["HELLO", "WORLD"] end @tag :pending test "accumulate reversed strings" do fun = fn w -> String.reverse(w) end words = ~w(the quick brown fox etc) expected = ["eht", "kciuq", "nworb", "xof", "cte"] assert Accumulate.accumulate(words, fun) == expected end @tag :pending test "nested accumulate" do chars = ~w(a b c) nums = ~w(1 2 3) fun = fn c -> Accumulate.accumulate(nums, &(c <> &1)) end expected = [["a1", "a2", "a3"], ["b1", "b2", "b3"], ["c1", "c2", "c3"]] assert Accumulate.accumulate(chars, fun) == expected end end
ExUnit.start() ExUnit.configure(exclude: :pending, trace: true)
defmodule Accumulate do @doc """ Given a list and a function, apply the function to each list item and replace it with the function's return value. Returns a list. ## Examples iex> Accumulate.accumulate(, fn(x) -> x * 2 end)  iex> Accumulate.accumulate([1, 2, 3], fn(x) -> x * 2 end) [2, 4, 6] """ @spec accumulate(list, (any -> any)) :: list def accumulate(, _), do:  def accumulate([head | tail], func) do [func.(head) | accumulate(tail, func)] end end
A huge amount can be learned from reading other people’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.