Erlang

Erlang is a functional, concurrent programming language designed for building robust, distributed, and fault-tolerant systems. It runs on the BEAM virtual machine, which is also used by Elixir.

What Makes Erlang Unique?

• Original BEAM Language: Erlang was the first language designed for the BEAM, and its concurrency, distribution, and fault-tolerance features are foundational (see “Concurrency and the BEAM” in the Elixir page).
• Lightweight Processes: Erlang processes are extremely lightweight and isolated, communicating only via message passing.
• Hot Code Swapping: Erlang supports updating code in a running system without downtime.
• “Let it Crash” Philosophy: Fault tolerance is achieved by isolating failures and using supervisors (see “Fault Tolerance” in the Elixir page).

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Basic Syntax

Variables and Immutability

• Variables are immutable and must start with an uppercase letter.

X = 1,
X = 2.  % Error: no rebinding allowed

Pattern Matching

• Used for assignment, function heads, and case expressions.

{A, B} = {1, 2}.  % A = 1, B = 2
 
% Function with pattern matching
add({A, B}) -> A + B.

Anonymous Functions

Add = fun(A, B) -> A + B end,
Add(1, 2).  % 3

No Pipe Operator

• Erlang does not have a pipe operator like Elixir’s |>, but function chaining can be done via nested calls.

Control Flow

if
  true -> yes;
  false -> no
end.
 
case {1, 2, 3} of
  {4, 5, 6} -> no_match;
  {1, X, 3} -> {matched, X}
end.

Recursion (No Loops)

sum([]) -> 0;
sum([H|T]) -> H + sum(T).

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Concurrency and the BEAM

• See the “Concurrency and the BEAM” section in the Elixir page for a conceptual overview.
• Syntax for spawning processes and message passing in Erlang:

Pid = spawn(fun() -> io:format("Hello from a process~n") end).
 
Pid ! {hello, "Hi there!"}.
 
receive
  {hello, Msg} -> io:format("~s~n", [Msg])
end.

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Metaprogramming

• Erlang does not have macros like Elixir, but supports parse transforms for advanced code manipulation (less common in everyday code).

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Summary Table: Erlang vs. Elixir

Feature	Erlang	Elixir
Syntax	Prolog-like, terse	Ruby-like, expressive
Variable Binding	Single assignment	Rebinding allowed
Pipe Operator	No	Yes (|>)
Macros	Parse transforms	Hygienic macros
Community	Telecom, infrastructure	Web, general purpose

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See Also

• For BEAM, concurrency, and fault-tolerance concepts, see the relevant sections in the Elixir page.
• For more on Functional Programmingbasics, see “Basic Syntax” in the Elixir page.