The Erlang Programming Language

Erlang

Practical functional programming for a parallel world

What is Erlang/OTP?

Erlang is a programming language used to build massively scalable soft real-time systems with requirements on high availability. Some of its uses are in telecoms, banking, e-commerce, computer telephony and instant messaging. Erlang’s runtime system has built-in support for concurrency, distribution and fault tolerance. Erlang Quickstart

OTP is set of Erlang libraries and design principles providing middle-ware to develop these systems. It includes its own distributed database, applications to interface towards other languages, debugging and release handling tools. Get started with OTP

Overview

fact(0) -> 1;              %% Pattern matching for control-flow
fact(N) -> N * fact(N-1).  %% Recursion to create loops
 
> example:fact(10).        %% Interactive shell for fast iterations
3628800
> [{I, example:fact(I)} || I <- lists:seq(1,10)].
[{1, 1}, {2, 2}, {3, 6}, {4, 24}, {5, 120}, {6, 720},
 {7, 5040}, {8, 40320}, {9, 362880}, {10, 3628800}]

> Fruits = ["banana","monkey","jungle"].     %% Immutable variables
["banana","monkey","jungle"]
> lists:map(fun string:uppercase/1, Fruits). %% Map values using stdlib functions
["BANANA","MONKEY","JUNGLE"]
%% Fold over lists using custom functions
> lists:foldl(fun(Str, Cnt) -> string:length(Str) + Cnt end, 0, Fruits).
18

> Parent = self().                         %% Get own process id
<0.376.0>
> Child = spawn(fun() -> receive go -> Parent ! lists:seq(1,100) end end).
<0.930.0>
> Child ! go.                              %% Send message to child
go
> receive Reply -> Reply end.              %% Receive response from child
[1,2,3,4,5,6,7,8,9,10,11|...]

%% Find even numbers
-spec even(list(integer())) -> list(integer()).
even(Numbers) ->
  mapreduce(Numbers, fun(Number) -> Number rem 2 == 0 end).
mapreduce(Numbers, Function) ->
  Parent = self(),
  [spawn(fun() -> Parent ! {Number, Function(Number)} end) || Number <- Numbers],
  lists:flatten(
    [receive {Number, true} -> Number; _ -> [] end || Number <- Numbers]).