erlang_cheat_sheet.md

Erlang Cheat Sheet

(this is a work in progress)

Running Erlang

Getting the interpreter in ubuntu: sudo apt-get install erlang. To get native compliation capability, also install erlang-base-hipe.

Starting the interpreter: erl. To exit: Ctrl-g then q enter.

File extension: .erl.

Compiling a module from the shell (assuming the module is in the current directory): c(module_name). If hipe is installed, native compliation can be done with c(module_name, [native]).

Working with Erlang

Add .beam to the project's .gitignore.

Emacs

• Start a shell: C-c C-z
• Compile file: C-c C-k

Syntax

Statements end in ..

Variables start with an upper case letter, atoms start with a lowercase one.

Math and Logic

• Mod operator: 5 rem 2
• Integer division: 5 div 2
• Equality testing: x =:= 2
• Pattern patching: {foo, X} = {foo, 123}. (X becomes 123)

Functions

• Functions with the same name but a different number of arguments are considered different functions.
  • e.g. add/2 vs add/3 for referring to the 2- and 3-argument variants

Example:

add(A,B) ->
    A + B.

Data structures

Tuples

Point = {123,456}. {X,Y} = Point. {X,_} = Point.

Lists

Lists can be mixed-type.

• List of numbers: [1, 2, 3]
• Prepend to a list [0 | numbers]
• Get head and tail: [H, T] = Numbers.
• Comprehensions: [2*N || N <- [1,2,3,4]].
• Range: lists:seq(1, 4).

Code structure

Modules

• Declare a module called foo: -module(foo).
• Export a function: -export([add/2]).
• Import a module and some functions: -import(foo, [add/2]).
• Calling a function from a module: foo:add(1,2).

Types

• Strongly typed (no implicit type conversions)
• Dynamically typed

Conversion

• erlang:list_to_integer("54") (strings are basically lists of numbers in erlang)
• erlang:integer_to_list(54)
• erlang:atom_to_list(true)

Interesting types

• Atoms (e.g. foo, true)
• Bit strings