Erlang Cheat Sheet

Core Erlang syntax covering modules, pattern matching, recursion, and the actor-model process/message-passing primitives.

2 PagesAdvancedMar 28, 2026

Modules & Functions

A minimal Erlang module.

erlang

%% hello.erl-module(hello).-export([world/0]).world() ->    io:format("Hello, World!~n").%% In the shell:%% 1> c(hello).%% 2> hello:world().

Pattern Matching

Single-assignment variables and function clauses.

erlang

%% Variables bind once (single assignment)X = 5,{A, B} = {1, 2},           %% tuple pattern matchfactorial(0) -> 1;factorial(N) when N > 0 -> N * factorial(N - 1).describe({ok, Value}) -> Value;describe({error, Reason}) -> Reason.

Processes & Messages

Spawning lightweight processes and sending messages.

erlang

%% Spawn a process and send it messagesPid = spawn(fun loop/0),Pid ! {self(), hello},loop() ->    receive        {From, hello} ->            From ! {self(), world},            loop();        stop ->            ok    end.

Modules & Attributes

Common module-level declarations.

-module(name).- Declares the module; must match the filename
-export([f/1]).- Exposes function f with arity 1 publicly
-record(point, {x, y}).- Defines a record type
io:format("~p~n", [Term])- Print a formatted term followed by a newline
spawn/1- Creates a new lightweight process
receive ... end- Blocks waiting for a matching message

Data Types

Erlang's built-in term types.

Atom- Constant literal, e.g. ok, error, undefined
Tuple- Fixed-size grouping, e.g. {ok, Value}
List- e.g. [1, 2, 3], built from recursive cons cells
Binary- e.g. <<1,2,3>>, a raw byte sequence
PID- Process identifier returned by spawn
Map- e.g. #{key => value}, a key/value store

Pro Tip

Lean on 'let it crash' — wrap risky work in a supervised process instead of defensive try/catch everywhere; OTP supervisors restart failed processes automatically.

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