epipe's Introduction

epipe

Erlang pipes

Influenced by Elixir pipe (|>) and with operators. Brings similar functionality to erlang

Intro

Probably you've seen code like this:

case gen_tcp:connect(Host, Port, Otps) of
    {ok, Socket} -> 
        case do_handshake(Socket) of
            ok -> send_message(Socket);
            {error, Reason} -> exit(normal)
        end;
    {error, Reason} -> exit(normal)
end

Sometimes the amount of the nested cases goes even deeper.... Which makes the code quite complex for understanding and debugging.

Epipe allows to rewrite it in a very flat way:

connect({Host, Port, Opts}) -> 
    case gen_tcp:connect(Host, Port, Otps) of
        {ok, Socket} -> {ok, Socket};
        {error, Reason} -> {error, Reason}
    end.

handshake(Socket) -> 
    case do_handshake(Socket) of
        ok -> {ok, Socket};
        {error, Reason} -> {error, Reason}
    end.

send_message(Socket) ->
    case do_send_message(Socket) of
        response -> {ok, response};
        Error -> {error, Error}
    end.

FunctionsList = [
    {connect_fun, fun connect/1}, 
    {handshake_fun, fun handshake/1}, 
    {send_message_fun, fun send_message/1}
],
epipe:run(FunctionsList, {Host, Port, Opts}).

Which allows to 'pipe' the initial data through FunctionsList, stopping on any step which would produce {error, ...} value.

Examples

sample1() -> 
    Fun1 = fun(Val) -> {ok, Val + 1} end,
    Fun2 = fun(Val) -> {ok, Val + 2} end,
    epipe:run([{add_one, Fun1}, {add_two, Fun2}], 0).

Would produce {ok, 3}

sample2() -> 
    Fun1 = fun(Val) -> {ok, Val + 1} end,
    Fun2 = fun(Val) -> {error, "Can't process data"} end,
    epipe:run([{step1, Fun1}, {step2, Fun2}, {step3, Fun1}], 0).

Would produce {error, step2, "Can't process data", 1}, giving not only error reason, but also would give a hint, about the failing step.