fork download
copy 
  1. defmodule Drop do
  2.   @doc ~S"""
  3.   Drop Function.
  4.   Similar to `Stream.drop`, but STRICTLY drops first `n` elements (n > 0).
  5.  
  6.   ## Examples
  7.  
  8.     iex> Sequences.fibs |> Drop.drop(5) |> Enum.take(5)
  9.     [8, 13, 21, 34, 55]
  10.   """
  11.   def drop(enum, count) do
  12.     fun = fn
  13.       (v, 0) -> {:suspend, v}
  14.       (_, n) -> {:cont, n - 1}
  15.     end
  16.     case Enumerable.reduce(enum, {:cont, count - 1}, fun) do
  17.       {:halted, _} -> []
  18.       {:done, _}   -> []
  19.       {:suspended, _, next_fun} -> &do_drop(next_fun, &1, &2)
  20.     end
  21.   end
  22.  
  23.   defp do_drop(_, {:halt, acc}, _fun), do: {:halted, acc}
  24.   defp do_drop(next, {:suspend, acc}, fun) do
  25.     {:suspended, acc, &do_drop(next, &1, fun)}
  26.   end
  27.   defp do_drop(next, {:cont, acc}, fun) do
  28.     case next.({:cont, 0}) do
  29.       {:halted, _} -> {:halted, acc}
  30.       {:done, _} -> {:done, acc}
  31.       {:suspended, v, next_fun} -> do_drop(next_fun, fun.(v, acc), fun)
  32.     end
  33.   end
  34.  
  35.   # fibs from Sequences.ex
  36.   defp fibs do
  37.     &fibs({1, 1}, &1, &2)
  38.   end
  39.  
  40.   defp fibs(_, {:halt, acc}, _fun), do: {:halted, acc}
  41.   defp fibs(v, {:suspend, acc}, fun), do: {:suspended, acc, &fibs(v, &1, fun)}
  42.   defp fibs({a, b}, {:cont, acc}, fun), do: fibs({b, a + b}, fun.(a, acc), fun)
  43.  
  44.   def run do
  45.     IO.puts "enum0 = fibs |> Stream.map(&IO.inspect/1)"
  46.     enum0 = fibs |> Stream.map(&IO.inspect/1)
  47.     IO.puts "enum1 = enum0 |> drop(5)"
  48.     enum1 = enum0 |> drop(5)
  49.     IO.puts "enum1 |> Enum.take(5) |> IO.inspect"
  50.     enum1 |> Enum.take(5) |> IO.inspect
  51.     IO.puts "enum1 |> Enum.at(5) |> IO.inspect"
  52.     enum1 |> Enum.at(5) |> IO.inspect
  53.   end
  54. end
  55.  
  56. Drop.run
Success #stdin #stdout 0.89s 106432KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
enum0 = fibs |> Stream.map(&IO.inspect/1)
enum1 = enum0 |> drop(5)
1
1
2
3
5
enum1 |> Enum.take(5) |> IO.inspect
8
13
21
34
55
[8, 13, 21, 34, 55]
enum1 |> Enum.at(5) |> IO.inspect
8
13
21
34
55
89
89
https://ideone.com/DYG3qz
language:
Elixir (elixir 1.8.2)
created:
8 years ago
visibility:
secret

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!