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Contents
defmodule ListOps do
# Please don't use any external modules (especially List) in your
# implementation. The point of this exercise is to create these basic functions
# yourself.
#
# Note that `++` is a function from an external module (Kernel, which is
# automatically important`) and so shouldn't be used either.
@spec count(list) :: non_neg_integer
def count(l), do: do_count(l, 0)
defp do_count([], acc), do: acc
defp do_count([_|t], acc), do: do_count(t, acc+1)
@spec reverse(list) :: list
def reverse(l), do: do_reverse(l, [])
defp do_reverse([], acc), do: acc
defp do_reverse([h|t], acc), do: do_reverse(t, [h|acc])
@spec map(list, (any -> any)) :: list
def map(l, f), do: do_map(l, f, []) |> reverse()
defp do_map([], _, acc), do: acc
defp do_map([h|t], f, acc), do: do_map(t, f, [f.(h)|acc])
@spec filter(list, (any -> as_boolean(term))) :: list
def filter(l, f), do: do_filter(l, f, []) |> reverse()
defp do_filter([], _, acc), do: acc
defp do_filter([h|t], f, acc) do
if f.(h) do
do_filter(t, f, [h|acc])
else
do_filter(t, f, acc)
end
end
@type acc :: any
@spec reduce(list, acc, ((any, acc) -> acc)) :: acc
def reduce([], acc, _), do: acc
def reduce([h|t], acc, f), do: reduce(t, f.(h, acc), f)
@spec append(list, list) :: list
def append(a, b), do: do_append(reverse(a), b)
defp do_append([], b), do: b
defp do_append([h|t], b), do: do_append(t, [h|b])
@spec concat([[any]]) :: [any]
def concat(ll), do: reverse(ll) |> reduce([], &(append(&1, &2)))
end
Version data entries
327 entries across 327 versions & 1 rubygems