take.erl

-module(take).
-export([take/2]).
-include_lib("eunit/include/eunit.hrl").

-spec take(integer(), [T]) -> [T].
take(Count,List) when count >= 0 ->
    takeTailRec(Count, List, []).

% there is nothing to take from source list, so return what we have
takeTailRec(_CountLeft, [], ResultAcc) ->
    lists:reverse(ResultAcc);
% requested count has been taken, so return
takeTailRec(0, _List, ResultAcc) ->
    lists:reverse(ResultAcc);
% taking one more element from source and adding it to resulting accumulator.
takeTailRec(CountLeft, [E|Ex], ResultAcc) ->
    takeTailRec(CountLeft - 1, Ex, [E|ResultAcc]).

% some tests. on ubuntu I had to install "sudo apt-get install erlang-eunit erlang-dev" and restart current erlang shell. (perhaps installing erlang-dev was not nesseray)
take0empty_test() -> ?assert(take(0,[]) == []).
take0nonEmpty_test() -> ?assert(take(0,[$H,$e,$l,$l,$o]) == []).
take1empty_test() -> ?assert(take(1,[]) == []).
take1nonEmpty_test() -> ?assert(take(1,[$H,$e,$l,$l,$o]) == [$H]).
take3nonEmpty_test() -> ?assert(take(3,[$H,$e,$l,$l,$o]) == [$H,$e,$l]).
take13nonEmpty_test() -> ?assert(take(13,[$H,$e,$l,$l,$o]) == [$H,$e,$l,$l,$o]).