a35.erl

-module(a35).
-export([doubleAll/1, evens/1, product/1,zip/2,zip_with/3,zip_with_map/3,zip_with_zip_with/2]).
-include_lib("eunit/include/eunit.hrl").
-created_by("Marcelo Ruiz Camauër").

%%% invoke with:
%%% a35:test().

%%% higher order functions
%%% Define the functions doubleAll, evens, and product using the higher-order 
%%% functions lists:map, lists:filter and lists:foldr.

%doubleAll([]) -> [];
%doubleAll([X|Xs]) ->
%    [ 2*X | doubleAll(Xs) ].

doubleAll(L) ->
   lists:map(fun(X) -> 2*X end,L).

doubleAll_test()->
    ?assertEqual([2,4,6],doubleAll([1,2,3])),
    ok.

%evens([]) -> [];
%evens([X|Xs]) when X rem 2 == 0 ->
%    [X | evens(Xs) ];
%evens([_|Xs]) ->
%    evens(Xs).

evens(L) ->  lists:filter(fun(Y) -> Y rem 2 =:= 0 end, L).

evens_test()->
    ?assertEqual([2,4],evens([2,3,4,5])),
    ok.

%product([]) -> 1;
%product([X|Xs]) -> X * product(Xs).

product(L)->lists:foldr(fun(X,Partial) -> X * Partial end,1,L).
product_test()->
    ?assertEqual(120,product([2,3,4,5])),
    ok.

% Zipping
% a) Define a function zip/2 that “zips together” pairs of elements from two lists like this:
% 
% zip([1,3,5,7], [2,4]) = [ {1,2}, {3,4} ]
% where you can see that the elements from the longer list are lost.
zip(_,[]) -> [];
zip([],_) -> [];
zip([X|Xs],[Y|Ys]) -> [{X,Y}|zip(Xs,Ys)].

zip_test()->
    ?assertEqual([ {1,2}, {3,4} ],zip([1,3,5,7], [2,4])),
    ok.
% 
% b) Define a function zip_with/3 that “zips together” pairs of elements from two lists using the 
% function in the first argument, like this:
% zip_with(fun(X,Y) -> X+Y end, [1,3,5,7], [2,4]) = [ 3, 7 ]
% (thanks Peer Reynders)
zip_with(_,[],_) -> [];
zip_with(_,_,[]) -> [];
zip_with(F,[X|Xs],[Y|Ys]) -> [F(X,Y)|zip_with(F,Xs,Ys)].

zip_wth_test()->
    ?assertEqual([{1,2},{3,4}],zip([1,3,5,7], [2,4])),
ok.

% c) Re-define the function zip_with/3 using zip and lists:map.
zip_with_map(F,X,Y)->
    lists:map(fun({A,B}) -> F(A,B) end, zip(X,Y)).

% d) Re-define zip/2 using zip_with/3.

zip_with_zip_with(A,B) ->
    zip_with(fun (X,Y) -> {X,Y} end,A,B).