test_helper.erl

test_helper.erl

-module(list_helper).
-author("granolocks").
-export([ 
    test/0,
    test/1,
    test/2,
    index/2
  ]).


%% Based on ruby index behavior as follows: 
%%
%%  2.1.2 :016 > a = [1,2,3,4,5]
%%  => [1, 2, 3, 4, 5]
%%  2.1.2 :017 > keys = [-6,-5,-1,0,4,5]
%%  => [-6, -5, -1, 0, 4, 5]
%%  2.1.2 :018 > keys.map{|k| a[k]}
%%  => [nil, 1, 5, 1, 5, nil]
%%
%%  %% Note: I am replacing nil with false.
%%
test() ->
  List  = [1,2,3,4,5],
  Tests = [
    {index(-6,  List),  false},
    {index(-5,  List),  1},
    {index(-1,  List),  5},
    {index(0,   List),  1},
    {index(4,   List),  5},
    {index(5,   List),  false},
  
    {i(-6,      List),  false},
    {i(-5,      List),  1},
    {i(-1,      List),  5},
    {i(0,       List),  1},
    {i(4,       List),  5},
    {i(5,       List),  false},

    {x(-6,      List),  false},
    {x(-5,      List),  false},
    {x(-1,      List),  false},
    {x(0,       List),  1},
    {x(4,       List),  5},
    {x(5,       List),  false}
  ], test(Tests).

test(Tests) -> 
   [ test(A, B) || {A, B} <- Tests] =:= [ true || _ <- Tests ].

test(X,X) -> io:format("test passed for ~p~n", [X]), true;
test(_,X) -> io:format("test failed for ~p~n", [X]), false.
 
index(Index,List) when Index < 0 -> 
  index((abs(Index)-1), lists:reverse(List));
index(_,[]) -> false;
index(0,[Head|_]) -> Head;
index(Index,[_|Tail]) -> index(Index-1,Tail).

%% minified
i(I,L)when I<0->i(abs(I)-1,lists:reverse(L));i(_,[])->false;i(0,[H|_])->H;i(I,[_|T])->i(I-1,T).

%% minified, no negative lookups
x(I,_)when I<0->false;x(_,[])->false;x(0,[H|_])->H;x(I,[_|T])->x(I-1,T).