Erlang Cheatsheet
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1Erlang CheatSheet v1.0
Variable % comments (starts with upper case)
atom or ‘ATOM’
Str = “John Doe”. % strings are stored as
Macros:
integers.
-define(macro1, Replacement)
?macro1 % to use the macro
% Writing the value on output
Erlang Shell:
Io:format(“Name is: ~s~n”, [Str]).
c(ModuleName) % compile module on erlang
Io:fwrite(“Name is: ~s~n”, [Str]).
shell
~n => new line
cd(“dirname”) % change directory on shell
~s => string
f() to clear all existing bindings
~f => float
rr("records.hrl") to read a records file
~w=>standard output. Like Object.toString().
rf(record_name) to forget a record
~p=>like ~w but breaks after each line
List = [1,2,3,4]. % lists
Records:
NewList = [6, 7, List] returns [6,7, [1,2,3,4]] %
-record(todo, {status=reminder,who=john,text}).
appends to a new list
- to create an instance of record: X =
29> [H|T] = AList.
#todo{status=urgent}.
["a","b",{1,2,3}] % returns the Head and Tail. H
- extracting values from record is similar to
and T are Unbound variables.
pattern matching
- X#todo.status %% to get a single value.
Tuple = {1.0, 2.0, 3.0}
- ++ is the infix append operator
element(2, Tuple) returns 2.0 % tuple index
- [1] ++ [2] ++ [3] = [1,2,3]
{_, Second, _} = Tuple stored 2.0 in Second
- X--Y is the list subtraction operator. It subtracts
variable % pattern matching to retrieve a value
the elements of Y from X.
List and Tuple can contain any type.
Use pattern matching/recursion to replace
Atuple = {1,2,3}.
iteration.
{1,2,3}
total([{What,N|T}]) -> cost(What) * N + total(T);
AList = ["a", "b", Atuple].
total([]) -> 0.
["a","b",{1,2,3}]
Anewtuple = {atom1, atom2, AList}.
{atom1,atom2,["a","b",{1,2,3}]
Functions:
File attributes % -import, -export, -module
Anonymous:
-module(ModuleName)
F = fun(X) -> X end. % F(10) prints 10
-export([Func_a/0, Func_b/1]).
Named:
- import to import the module and methods % -
method_name(Arg) ->
import(lists, [map/2]).
Arg.
- Includes File: -include(Filename). % -
include_lib(Name).
case Expression of
% Perform action on each element on list
L = [1,2,3,4,5].
Pattern1 [when Guard1] -> Expr_seq1;
[1,2,3,4,5]
Pattern2 [when Guard2] -> Expr_seq2
lists:map(fun(X) -> 2*X end, L). % using map
end.
method of lists module
[2,4,6,8,10]
45> [2*X || X <- L]. % or using list
comprehensions
[2,4,6,8,10]
Nauman Leghari
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