Academic problems solved with Erlang

collatz.erl

%% https://en.wikipedia.org/wiki/Collatz_conjecture
-module(collatz).

-export([collatz/1]).

collatz(N) -> collatz(N,0,[N]).

collatz(1, C, Acc) -> {C, lists:reverse(Acc)};
collatz(N, C, Acc) ->
  R = case is_even(N) of
    true  -> trunc(N/2);
    false -> trunc(N*3 + 1)
  end,
  collatz(R, C+1, [R|Acc]).

is_even(I) -> I rem 2 =:= 0.

compose.erl

-module(compose).
-export([compose/0, compose/1]).

compose()   -> compose([]).
compose([]) -> fun(X) -> X end;
compose(L)  -> fun(X) -> lists:foldr(fun(F, V) -> F(V) end, X, L) end.

curry.erl

%% https://en.wikipedia.org/wiki/Currying
-module(curry).

-export([curry_simpl/1, curry/1]).

curry_simpl(F) -> curry_simpl(F, []).
curry_simpl(F, Args) ->
  {arity,Arity} = erlang:fun_info(F, arity),
  case length(Args) == Arity of
    true  -> apply(F, Args);
    false -> fun (Arg) -> curry_simpl(F, Args ++ [Arg]) end
  end.

curry(F) when is_function(F) -> curry(F, []).
curry(F, Args) when is_function(F), is_list(Args)->
  {arity,Arity} = erlang:fun_info(F, arity),
  case length(Args) >= Arity of
    true  -> apply(F, lists:sublist(Args, Arity));
    false -> fun(Arg) -> curry(F, lists:flatten([Args, Arg])) end
  end.

fib.erl

%% https://en.wikipedia.org/wiki/Fibonacci_number
-module(fib).

-export([fib/1]).

fib(N) when N > 0 -> fib(N, 1, 0, 1).

fib(1, _, _, _)         -> 1;
fib(2, _, _, _)         -> 1;
fib(N, N, _, Prev)      -> Prev;
fib(N, C, Prev2, Prev)  -> fib(N, C+1, Prev, Prev2+Prev).

is_proplist.erl

-module(is_proplist).
-export([is_proplist/1]).

is_proplist(L) when is_list(L) ->
  lists:all(fun
              ({K,_}) when is_atom(K)   -> true;
              ({K,_}) when is_binary(K) -> io_lib:printable_latin1_list(binary_to_list(K));
              (_)                       -> false
            end, L);
is_proplist(_)                 -> false.

lazy.erl

-module(lazy).
-compile(export_all).

%% generator(F, V) -> fun() -> [ V | generator(F,  F(V)) ] end.
generator(F, V) -> [V | fun() -> generator(F, F(V)) end].

take(N, G) when N >= 0 -> lists:reverse(take(N, G, 0, [])).

take(_,[],_,Acc) -> Acc;
take(N,_,N,Acc)  -> Acc;
take(N, [H|T], C, Acc) when is_function(T) -> take(N, T(), C+1, [H|Acc]);
take(N, [H|T], C, Acc) -> take(N, T, C+1, [H|Acc]).

take.erl

%% Take N first elements of list
-module(take).

-export([take/2]).

take(N, L) when N > 0 -> lists:reverse(take(N, L, 0, [])).

take(_,[],_,Acc) -> Acc;
take(N,_,N,Acc)  -> Acc;
take(N, [H|T], C, Acc) -> take(N, T, C+1, [H|Acc]).

zip_with.erl

%% http://learnyouahaskell.com/higher-order-functions#higher-orderism
-module(zip_with).

-export([zip_with/3]).

zip_with(F, L1, L2) ->
  lists:reverse(zip_with(F, L1, L2, [])).

zip_with(_,[],_,Acc) -> Acc;
zip_with(_,_,[],Acc) -> Acc;
zip_with(F, [H1|T1], [H2|T2], Acc) -> zip_with(F, T1, T2, [F(H1,H2) | Acc]).

my Erlang snippets storage

Just added curry.erl with Erlang currying inside, do not miss it!
https://gist.github.com/cystbear/b27bc5754ffa11fec634#file-curry-erl

Just added compose.erl file. Function Composing implementation.
https://gist.github.com/cystbear/b27bc5754ffa11fec634#file-compose-erl