erlang

Critical Patterns

OTP GenServer (REQUIRED)

-module(counter).
-behaviour(gen_server).
-export([start_link/0, increment/0, get/0]).
-export([init/1, handle_call/3, handle_cast/2]).

start_link() ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

init([]) -> {ok, 0}.

handle_call(get, _From, State) ->
    {reply, State, State}.

handle_cast(increment, State) ->
    {noreply, State + 1}.

Supervisor (REQUIRED)

-module(my_sup).
-behaviour(supervisor).
-export([start_link/0, init/1]).

start_link() ->
    supervisor:start_link({local, ?MODULE}, ?MODULE, []).

init([]) ->
    SupFlags = #{strategy => one_for_one, intensity => 5, period => 10},
    Children = [
        #{id => worker, start => {my_worker, start_link, []}}
    ],
    {ok, {SupFlags, Children}}.

Decision Tree

Need request/response?     → Use gen_server call
Need fire-and-forget?      → Use gen_server cast
Need supervision?          → Use supervisor behavior
Need state machine?        → Use gen_statem
Need event handling?       → Use gen_event

Commands

erl                         # Start REPL
erlc module.erl            # Compile
rebar3 compile             # Build project
rebar3 shell               # Interactive shell

Resources

• Concurrent Programming: concurrent-programming.md
• Fault Tolerance: fault-tolerance.md
• OTP Patterns: otp-patterns.md