Elixir is a programming language built on top of Erlang. As Erlang, it is a functional language with strict evaluation, single assignment and dynamic typing built to support distributed, fault-tolerant, non-stop applications with hot swapping. Elixir allows you to invoke Erlang modules without a need to convert data types, therefore there is no hit in performance when invoking existing Erlang code.
The main difference between Elixir and Erlang is syntax and object orientation. Elixir provides a very simple Object Model based on prototype languages with most of its syntax inspired by Ruby.
Elixir is still in development. If you want to help building it or are just looking for some fun, you can get started now! First, you need to clone this repository to your machine, compile and test it:
$ git clone https://github.com/josevalim/elixir.git
$ cd elixir
$ make test
$ bin/elixir -v
Elixir 0.2.1.dev
If tests fail, it is likely you have an outdated Erlang version. You can check your Erlang version by calling erl in the command line. You will see some information as follow:
Erlang R14B01 (erts-5.8.2) [source] [64-bit] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false]
Elixir requires Erlang R14B01 or later version to execute (R14A and R14B do not work). If you have the correct version and tests still fail, feel free to open an issue in the issues tracker on Github. If all tests pass, you are ready to play with Elixir!
This README provides a length explanation about Elixir in the Learning Elixir section below. There are also some examples in the examples folder that you can run by executing the bin/elixir EXAMPLE and an interactive Elixir available as bin/iex. Feel free to build your own examples and study the language better.
Currently, there is an effort to improve Elixir Standard Library. As much of Elixir's STDLIB is written in Elixir and tested in Elixir, you don't need to be an advanced Erlang user to improve the language, just know the OTP a bit. As an example, you may take a look at the List implementation and its tests to check how simple it is.
If you want to contribute to Elixir, the code is organized as follow:
-
include,src- Both directories contain the part of the source code written in Erlang.leexandyeccwere used as tokenizer and parser respectively; -
lib- Contains Elixir's STDLIB, written in Elixir; -
test/elixir- Tests for Elixir's STDLIB, written in Elixir. For this purpose, Elixir ships with a small unit test library calledExUnit; -
test/erlang- Contains tests for Elixir, written in Erlang. Usually, just internal stuff is tested here. The preferred way to test is in Elixir itself.
If you are interested, check out the ROADMAP.md file in the repository or keep reading this README to find items to be implemented.
- Textmate Bundle for Elixir: https://github.com/josevalim/elixir-tmbundle
This is a basic introduction into Elixir basic objects and object model. Some sections have a paragraph called "To be implemented", they represent parts of Elixir that was not implemented yet and that are under discussion.
This introduction borrowed its guidelines from Learn You Some Erlang, a great resource to learn Erlang which will be referenced several times during this introduction.
Let's start with a simple hello world. The first step is to create a new file called "hello.ex" inside Elixir repository with the following contents:
module Hello
def world
IO.puts "Hello World"
end
end
Now, we can compile this file to the current directory:
bin/elixirc hello.ex -o .
Notice that some .beam files were added to the current directory with the compiled code. We can execute it by invoking the method world in the module Hello in the same directory:
bin/elixir -e "Hello.world"
And you will see "Hello World" printed! This example works because Elixir automatically loads the compiled files in the current directory. If your compiled files are in other directories, you can pass those new directories to bin/elixir using -pa and -pz as options. Type bin/elixir with no arguments for more information.
When you are building libraries in Elixir, those are the main steps you should take. Write your code, compile it and run it! However, sometimes it is nice to just put some code together and run it, without a explicit compilation step. For that, elixir allows you to easily create scripts. Let's create a new file "hello.exs" with the following contents:
IO.puts "Hello World"
And now run it:
bin/elixir hello.exs
And it works again! Notice we used the extension .exs instead of .ex here. This is just a convention, Elixir does not treat .exs files differently from .ex files in any way! In fact, you could even try to compile the .exs file:
bin/elixirc hello.exs -o .
When you do that, you can see that "Hello World" is printed as well. This is because Elixir actually execute the files to compile them. This is the key to many Elixir features, as we are going to see later.
Also notice that Elixir also ships with an interactive console that you can use for most examples in this tutorial, you can start it with:
bin/iex
Enjoy!
Before we start, notice that comments in Elixir are, as in Erlang, done with %.
% This is a commented line
Throughout this introduction, % => represents the result of an expression:
1 + 1 % => 2
Elixir supports both Integer and Floats:
2 + 15 % => 17
- 13 * 10 % => -130
1986 - 1985 % => 1
5 / 2 % => 2.5
4 / 2 % => 2.0
Notice that, as Erlang, "/" always returns a Float. If you want to have integer-to-integer division and the modulo operator, you should use div and rem:
5 div 2 % => 2
5 rem 2 % => 1
Several operations can also be done in a single expression, obeying the normal precedence rules:
50 * 10 - 490 % => 10
(50 * 10) - 490 % => 10
-(50 * 10) - 490 % => -990
As in Ruby, everything is an object, so we can call methods on numbers:
-1.abs % => 1
5.div(2) % => 2
It comes as no surprise that + is also a method:
1.+(2) % => 3
Finally, notice that Elixir allows you to include "_" in numbers (as in Ruby). This improves the readability when working with large numbers:
1_052_672
- https://github.com/josevalim/elixir/tree/master/lib/integer.ex
- https://github.com/josevalim/elixir/tree/master/lib/float.ex
- https://github.com/josevalim/elixir/tree/master/lib/numeric.ex
Currently, there is no support to enter numbers in bases other than base 10. This is the current API in Erlang (although the best API for Elixir is under discussion):
2#101010. % => 42 8#0677. % => 447 16#AE. % => 174
Elixir also has Atoms, called Symbols in other languages like Ruby. Although its syntax was borrowed from Lisp:
'atom
'Atom
'atom_without_spaces
Atoms are literals, with their own value as name. An atom 'symbol is an atom 'symbol everywhere, with exactly the same value. Atoms start with a single quote and should not have spaces (spaces delimit the atom end). Atoms with spaces are represented by wrapping them in quotes:
'"Atom with Spaces"
As in Erlang and Ruby, Atoms are not garbage collected, so remember to not generate atoms dynamically, otherwise you will run out of memory sooner rather than later.
As in Erlang, the boolean values are simply atoms named true and false. However, to avoid writing 'true and 'false, Elixir also allows you to simply write true or false. The following are all equivalent and will yield 1 as result:
if 'true
1
else
2
end
if true
1
else
2
end
if 'false
2
else
1
end
if false
2
else
1
end
Besides those two boolean values, Elixir also has a nil value which is simply an atom as well. nil also evaluates to false in conditionals.
Tuples are used to organize many terms together when you know how many terms there are. As in Erlang, a tuple is written in the following form:
% A tuple containing all boolean values
{ true, false }
% A tuple that may represent a point with coordinates X and Y
{ 10, 20 }
% An empty tuple
{ }
Tuples and lists (which are going to see next), are zero-indexed in Elixir while they are one-indexed in Erlang. You can retrieve a specific element using []:
{'a,'b,'c}[1] % => 'b
{'a,'b,'c}[2] % => 'c
Lists are the main object in Elixir (as in any other functional language) and can contain anything:
% Some list with elements
['atom, 1, 2, 3, { 'some, 'tuple }]
% An empty list
[]
Elixir Standard Library has a bunch of methods to interact with lists:
[1, 2, 3].length % => 3
['a, 'b, 'c][1] % => 'b
As in Elixir + is simply a method like any other (and not an arithmetic operator as in Erlang), it can also be used to add arrays:
[1, 2, 3] + [4, 5, 6] % => [1,2,3,4,5,6]
Lists in Erlang and Elixir are implemented as linked lists. This means prepending an item to the list is quite fast, but appending is much slower. Therefore we have a special syntax to prepend one or more items to a list:
list = [2,3,4]
% Don't do this:
[1] + [2,3,4] % => [1,2,3,4]
[0,1] + [2,3,4] % => [0,1,2,3,4]
% Do this instead:
[1|list] % => [1,2,3,4]
[0,1|list] % => [0,1,2,3,4]
Most of the power in lists comes when used together with functions:
[1, 2, 3].map do (x)
x * 2
end % => [2, 4, 6]
[1, 2, 3].foldl 0, do (x, acc)
acc + x
end % => 6
The examples above uses functions using the do/end syntax. Don't worry about them now, we are going to take a better look at them later.
Elixir provides a first-class syntax to deal with ordered dictionaries (similar to Hashes in Ruby).
% A dict with 'a and 'b as keys and 1 and 2 as their respective values
{ 'a: 1, 'b: 2 }
% An empty dict
{:}
Elixir dictionary implementation is backed up by the orddict module in OTP. Notice that Erlang ordered dicts are not ordered in the order items are added, but rather using Erlang ordering of terms. You can learn more about Erlang ordering by reading this section from Learn You Some Erlang.
Ordered Dicts are recommended to deal with small amount of data. Other data structures are recommended to deal with a huge amount and you can read more about others key-value store, but remember that most of them are not implemented in Elixir yet.
Elixir has a similar syntax to Erlang for handling bit strings:
% A bit string with three elements
<<1, 17, 42>>
% Converting a bit string to a list
<<1, 17, 42>>.to_list % => [1, 17, 42]
Elixir also allows to specify the size for bit strings, using the same syntax as Erlang:
% A bit string with size 4, because we specify that 42 is a 16-bits segment
<<1, 17, 42:16>>
By default, the bit string type in both Elixir and Erlang is integer. That said, the following is invalid:
<<3.14>>
Instead, you need explicitly specify it as a float:
<<3.14|float>>
Notice the syntax above is a bit different from Erlang. Erlang uses / to specify the type, Elixir uses |. This allows Elixir, differently from Erlang, to have expressions inside bit string:
<<1+2>>
In general, everything that applies to Erlang bit string applies to Elixir bit string. You can read more about them on Erlang's documentation.
- <https://github.com/josevalim/elixir/tree/master/lib/bit string.ex>
- http://www.erlang.org/doc/programming_examples/bit_syntax.html
In Erlang, strings are a list of chars:
"hello" == [104, 101, 108, 108, 111]
This is expensive because each character uses 8 bytes of memory, not 8 bits! Erlang stores each character as a 32-bit integer, with a 32-bit pointer for the next item in the list.
Elixir takes a different approach to strings. Strings in Elixir are handled as UTF-8 binaries. Since a binary is nothing more than a bit string, where the number of bits is a multiple of 8, we can create strings using the bit string syntax:
<<72, 73, 74>> % => "HIJ"
When a bit string with multiple of 8 bits is created, it is automatically mapped to a string. However, you will rarely use the syntax above as Elixir provides the more traditional quote syntax to handle strings:
% The famous "hello world" string
"hello world"
% A string converted to a char list:
"hello".to_char_list % => [104, 101, 108, 108, 111]
% Convert a char list back to a binary/string:
[104, 101, 108, 108, 111].to_bin % => "hello"
% Notice that to_s in a list is not the same as to_bin.
% It returns the list represented as a string instead:
[104, 101, 108, 108, 111].to_s % => "[104,101,108,108,111]"
% Strings are UTF-8
"Arrow ⇧ up".length % => 10
Keep in mind that, as Elixir strings are different from Erlang strings, sometimes you may need to convert Elixir strings to a char list and vice-versa when invoking Erlang methods using the methods to_char_list and to_bin as seen above.
Finally, strings also support interpolation:
"string #{'with} interpolation" % => "string with interpolation"
"1 + 1 = #{1 + 1}" % => "1 + 1 = 2"
Functions are an important aspect of Elixir as in any functional programming language. Functions are created in Elixir with the keywords -> or do:
my_function = do
1 + 2
end
my_function.call() % => 3
another_function = ->
1 * 2
end
another_function.call() % => 2
Some functions expect arguments:
my_function = do (x, y)
x + y
end
my_function.call(1, 2) % => 3
another_function = -> (x, y)
x * y
end
another_function.call(1, 2) % => 2
You can also represent functions in one line, without a need for the closing keyword end:
my_function = do (x, y) x + y
my_function.call(1, 2) % => 3
another_function = -> (x, y) x * y
another_function.call(1, 2) % => 2
Notice that, whenever using one-line functions, if you need parenthesis inside the expression, you are required to give empty parenthesis arguments, for example:
% This works as expected:
my_function = -> 1 + 2
my_function.call % => 3
% This won't work and it raises a syntax error
my_function = -> (1 + 2)
% This works as well:
my_function = -> () (1 + 2)
In the second case, it is ambiguous if the parenthesis is part of the argument list or the function expressions. This is why you either need to remove parenthesis (as in the first example) or add empty parenthesis (as in the third example). This syntax quickly proves to be very convenient:
[1,2,3].map(-> (x) x * 2) % => [2,4,6]
In the example above, we are calling .map passing a function as argument. If we remove the optional parenthesis:
[1,2,3].map -> (x) x * 2 % => [2,4,6]
Other examples using the multiline syntax:
[1,2,3].foldl(0, do (x, acc)
acc + x
end) % => 6
Again, removing the parenthesis, improves readability:
[1,2,3].foldl 0, do (x, acc)
acc + x
end % => 6
Elixir also provides a shortcut syntax to invoke functions that is usually faster as it skips method lookup:
my_function = -> (x, y) x + y
my_function.(1, 2) % => 3
In such cases, parenthesis are always required.
Another useful extension Elixir adds to functions is the easy generation of anonymous functions. For instance, suppose you have a list of cars and you want to get their names. A way to do that would be:
cars.map -> (c) c.name
However, you can easily generate an anonymous functions that does the same:
cars.map _.name
Anonymous functions can also be generated with arguments, so the map expressions we saw above:
[1,2,3].map -> (x) x * 2 % => [2,4,6]
Could actually be rewritten as:
[1,2,3].map _.*(2)
Currently, functions do not support partial applications or pipes, but such features will be added down the road.
Variables in Elixir works differently from Erlang. You can assigned to them several times:
x = 1
x = 2
You can force a match to happen prefixing ~ to the variable name:
~x = 3 % => Raises a bad match error, because x was last bound to 2
In Erlang/Elixir terms, a variable that was not assigned yet is called unbound variable. Let's see more examples:
% Let's bound the variable x to 'foo
x = 'foo
% Now let's match a tuple with other tuple.
% Since x is already bound, we are comparing x with 'baz and it will fail:
{ ~x, y } = { 'baz, 'bar }
% In this case, we compare 'x with 'foo and it matches.
% Since y is unbound, we assign 'bar to it:
{ ~x, y } = { 'foo, 'bar }
x % => 'foo
y % => 'bar
For lists, we can use the same syntax to prepend an item on pattern matching, easily retrieving the head and tail:
[h|t] = [1,2,3]
h % => 1
t % => [2,3]
% Raises an error because h was already assigned to 1 and 1 does not match 2
[~h|t1] = [2,3,4]
Elixir will often complain if you bound a value to a variable but never use it. For instance, imagine that you want to get just the first element of a tuple with three items:
{x, y, z} = {1, 2, 3}
If you don't use the y and z variables, Elixir will show you some warnings. For this reason, you could use _ instead:
{x, _, _} = {1, 2, 3}
The variable _ is always unbound:
_ = 1
_ % => Raises that variable '_' is unbound
Sometimes having several occurrences of _ in the same expression is confusing, so you can do this instead:
{x, _y, _z} = {1, 2, 3}
The values 2 and 3 will be bound to the variables _y and _z, but Elixir won't complain if you eventually don't use them.
Keep in mind that the number of expressions allowed in pattern matching are limited. You cannot invoke methods, use interpolated strings, retrieve constants and so on. Therefore, this is invalid:
1.abs = -1
Ordered dicts are also allowed in pattern matching but there is one important restriction: you are responsible to make their order match. Therefore, this won't work:
dict = { 2: 4, 1: 2 }
{ 2: 4, 1: 2 } = dict
This fails because the dict variable is ordered, so it is actually represented as {1: 2, 2: 4}. Remember that OrderedDicts are ordered according to Elixir ordering of terms and not the order new items are added. This ordering rule is important to allow us to bound variables to key-values:
dict = { 2: 4, 1: 2 }
% This matches as the left expression is in the correct order
{ 1: 2, 2: 4 } = dict
% This matches and bound x and y to 2 and 4
{ 1: 2, x: y } = dict
Finally, pattern matching can also be implemented in methods signatures. Here is the classic Fibonacci example:
module Math
def fibonacci(0)
0
end
def fibonacci(1)
1
end
def fibonacci(n)
fibonacci(n - 1) + fibonacci(n - 2)
end
end
Math.fibonacci(0) % => 0
Math.fibonacci(1) % => 1
Math.fibonacci(3) % => 2
Math.fibonacci(10) % => 55
Notice the example above is not tail call optimized. We will discuss modules, methods and optimizations later.
Operators can be binary or unary operators:
(expression) binary_op (expression)
unary_op (expression)
Elixir term comparisons operators are close to Erlang ones, except !=, =!= and <= which maps to Erlang /=, =/= and =<.
| Operator | Description |
| == | equal to |
| != | not equal to |
| <= | less than or equal to |
| < | less than |
| >= | greater than or equal to |
| > | greater than |
| =:= | exactly equal to |
| =!= | exactly not equal to |
As in Erlang, Elixir can order different objects types:
number < atom < reference < fun < port < pid < tuple < any other object < list < bit string
Lists are compared element by element. Tuples are ordered by size, two tuples with the same size are compared element by element. If one of the compared terms is an integer and the other a float, the integer is first converted into a float, unless the operator is one of =:= and =!=.
All term comparison operators return a boolean expression.
| Operator | Description | Argument |
| + | unary + | number |
| - | unary - | number |
| + | any object | |
| - | any object | |
| * | any object | |
| / | returns a float | any object |
| div | returns an integer | any object |
| rem | returns an integer | any object |
Except by the two unary operators, all other operators accept any object as parameter. This is because those operators are implemented as methods and their implementation are defined by the object which is receiving the method. For instance, we can concatenate two lists by using the + operator:
[1,2,3] + [4,5,6] % => [1,2,3,4,5,6]
This is the same as:
[1,2,3].+([4,5,6]) % => [1,2,3,4,5,6]
Notice however that we cannot add a list with a number:
[1,2,3] + 1 % => Raises an error
Also, Elixir keeps the same semantics as Erlang in the sense the / operator always returns a float when numbers are given as argument. The div and rem operators are used to deal with integers:
2 / 1 % => 2.0
6 div 4 % => 1
6 rem 4 % => 2
To be implemented/written.
Elixir provides three operators that accept any object as argument. We will see later that some operators (inherited from Erlang) accept strictly boolean values.
| Operator | Description |
| && | and |
| || | or |
| ! | not |
Remember that any object, except false, evaluates to true:
!false % => true
!true % => false
!Object.new % => false
Both && and || are actually control structures. They do not return a boolean but the last evaluated object:
1 && 2 % => 2
true || false % => true
'atom || 'another % => 'atom
false || 'another % => 'another
false && IO.puts("I will never be executed")
1 || IO.puts("I will never be executed")
true || IO.puts("I will never be executed")
Elixir provides the following operators to deal strictly with booleans:
| Operator | Erlang equivalent | Description |
| and | and | Both expressions must return boolean |
| or | or | Both expressions must return boolean |
| andalso | andalso | First expression must return boolean, short-circuit operator |
| orelse | orelse | First expression must return boolean, short-circuit operator |
| not | not | Unary operators, expression must be a boolean |
Operator precedence in falling priority:
| Operator | Associativity |
| + - ! not | Non associative (unary operators) |
| / * div rem | Left |
| == != < <= > >= =:= =!= | Left |
| <- | Right |
| and andalso | Left |
| or orelse | Left |
| && | Left |
| || | Left |
Elixir, differently from Erlang, has a more conventional if/else structure:
list = [1,2,3]
if list.include?(4)
IO.puts "it includes 4"
elsif list.include?(5)
IO.puts "it includes 5"
else
IO.puts "it does not include 4 or 5"
end
Everything in Elixir, except false and nil, evaluates to true.
On the other hand, the case/match structure from Elixir is quite similar to Erlang's:
case {1,2,3}
match {3,2,x}
x * 2
match {1,2,x}
x * 2
end
As you can notice,case/match uses pattern matching. If no case expression matches, an error is raised. Elixir also allows an else clause in case/match, which is the same as match _:
case {4,5,6}
match {3,2,x}
x * 2
match {1,2,x}
x * 2
else
10
end
Finally, case/match expressions can be inlined and grouped, providing a more compact syntax:
case {4,5,6}
match {3,2,x}, {1,2,x} then x * 2
else 10
end
Currently there is no support for guard expressions as in Erlang, although it may be implemented at some point.
Similarly to Erlang, Elixir has three kinds of exceptions. They are raised with the methods (and not keywords!) throw, error and exit. You can read more about each type on Learn You Some Erlang.
To handle these exceptions, Elixir uses a syntax similar to Ruby:
try
self.throw {1,2}
catch {1,2}
IO.puts "Rescued {1,2}"
end
Similar to the match syntax, you can catch different values in the same clause:
try
self.throw {1,2}
catch {1,2}, {3,4}
IO.puts "Rescued a tuple"
end
In order to catch an error or an exit, you need to be explicit:
try
self.error {1,2}
catch {1,2}
IO.puts "I will never get a tuple {1,2}"
catch 'error: {1,2}
IO.puts "Rescue an error with {1,2}"
end
You must use the keyword after if you want to execute some code regardless if there was an exception or not:
try
self.error {1,2}
catch {1,2}
IO.puts "I will never get a tuple {1,2}"
after
IO.puts "I am always executed"
end
It is important to keep in mind that tail calls are not optimized inside try blocks. This is expected as the runtime needs to keep the backtrace in case an exception occur. Also, notice that variables created inside try/catch/after clauses do not leak to the outer scope.
try
foo = 13
end
foo % => raises undefined variable or local method foo error
try
foo = 13
after
IO.puts "I am always executed"
end
foo % => raises undefined variable or local method foo error
When used inside methods, the try/end can be omitted:
def some_method
self.error {1,2}
catch {1,2}
IO.puts "I will never get a tuple {1,2}"
after
IO.puts "I am always executed"
end
Again, be careful when using this pattern with tail calls, as the try block is not optimized. For instance, consider this method:
def some_method([h|t], value)
value = method_that_may_raise_error(h)
some_method(t, value)
catch {1,2}
IO.puts "I will never get a tuple {1,2}"
after
IO.puts "I am always executed"
end
It should actually be written as:
def some_method([h|t], value)
value = try
method_that_may_raise_error(h)
catch {1,2}
IO.puts "I will never get a tuple {1,2}"
after
IO.puts "I am always executed"
end
some_method(t, value)
end
Here is a list of runtime errors that can be raised by Elixir:
-
{ 'builtinnotallowed, { method, builtin } }Invoking
methodnot allowed on thebuiltinobject. Built-in objects are all objects that maps directly to Erlang ones, they are: String, Integer, Float, Tuple, List, OrderedDict and so forth. A few operations likemixin,protoand copy are not allowed on built-in objects; -
{ 'objectdefined, { name, file, line } }An object with
namewas already defined onfileatline. This is a common error to appear during compilation time as the following valid Ruby pattern is not valid in Elixir:module Foo module Bar end end module Foo module Baz end endIn the example above, we are reopening
Footo add aBazmodule. This is invalid in Elixir as modules cannot be reopened. To handle this, just defineBazdirectly asFoo::Baz:module Foo::Baz end -
{ 'reservedmodulename, name }Raised when you defined a module named
MixinorProtooutside of an Object. BothMixinandProtoare reserved modules names; -
{ 'nomethod, { name, arity, object } }There isn't a public method with the given
nameandarityinobject; -
{ 'nolocalmethod, { name, arity, module } }There isn't a local method with the given
nameandarityinmodule; -
{ 'notamodule, { method, object } }methodfailed becauseobjectis not a module; -
{ 'noconstant, name }A constant with
namecould not be found; -
{ 'nocallback, { name, arity, object } }The callback
namewitharitywas not implemented inobject. Raised when an object is given as callback but does not comply to all conditions; -
{ 'badivar, name }The
namegiven is not an atom and cannot be given as instance variable name; -
{ 'badinitialize, value }valuereturned byinitializeis not the same kind as the original object; -
{ 'badivars, value }valuegiven to@()orset_ivarsis not an OrderedDict or it is an OrderedDict but not all keys are atoms; -
{ 'moduledefined, { method, module } }Cannot invoke
methodinmodulebecause the module was already defined. For example, callingmodule_evalin an already defined module will raise such errors;
In Elixir, we have the following basic types related to Strings:
% Strings (utf8 by default and represented as binaries)
"string"
"string #{'with} interpolation" % => "string with interpolation"
% Integer representation of a character
$a % => 97
$b % => 98
$\\ % => 92
$\( % => 40
% A string represented as a list of chars (all four expressions below allow interpolation)
$"string" % => [115,116, 114, 105, 110, 103]
$(string) % => [115,116, 114, 105, 110, 103]
$[string] % => [115,116, 114, 105, 110, 103]
${string} % => [115,116, 114, 105, 110, 103]
% A binary representing the list of chars above
<<115, 116, 114, 105, 110, 103>>
% Erlang Atoms or Ruby Symbols
'atom
'"atom with space and interpolation"
'(atom with space and interpolation)
'[atom with space and interpolation]
'{atom with space and interpolation}
Besides these basic types, we also have string sigils. Here is one example:
% Regular expressions
%% Without interpolation
~r(regexp)
~r[regexp]
~r{regexp}
~r"regexp"
%% With interpolation
%% It also accepts [], {} and "" as separators as above
~R(regexp #{1 + 1} interpolation)
%% With regexp operators
~r(foo)im
All string sigils follow the same set of rules. They start with a ~ followed by a letter and the string is delimited by a separator. The available separators are (), [], {} and "". If the letter after ~ is lowercased, no interpolation is allowed, if uppercased, interpolation is allowed. A couple more examples:
% Another way to create strings
~q(string without interpolation)
~Q{string without interpolation}
% Another way to create atoms
~a"atom without interpolation"
~A[atom with interpolation]
% Another way to create a list of chars
~l(string) % => [115,116, 114, 105, 110, 103]
~L{string with interpolation}
% A list of words (to be implemented)
~w(foo bar baz) % => ["foo", "bar", "baz"]
~W{foo #{'bar} baz} % => ["foo", "bar", "baz"]
- https://github.com/josevalim/elixir/tree/master/lib/string.ex
- https://github.com/josevalim/elixir/tree/master/lib/atom.ex
- https://github.com/josevalim/elixir/tree/master/lib/regexp.ex
Elixir also has HEREDOCs to make easier to handle big strings:
string = ~~
This is a string which
preserves whitespace at
the beginning and also
handles #{'interpolation}
~~
Similar to Ruby, HEREDOCs allow an identifier right after the initial three quotes:
string = ~~HTML
<p>Nice!</p>
~~
This allows to identify the content and most text editor uses it to properly syntax highlight it. Besides, you can add Elixir code after the HEREDOC and they still are properly evaluated:
string = ~~STRING + "123"
abc
~~
string % => "abc\n123"
Consequently, this feature allows multiple HEREDOCs:
list = [~~ONE, ~~TWO, ~~THREE]
this is the first string
~~
this is another one
~~
this is the third. cool, isn't?
~~
list[0] % => "this is the first string\n"
list[1] % => "this is another one\n"
list[2] % => "this is the third. cool, isn't?\n"
Invoking Erlang methods with elixir is quite trivial:
% Accessing the is_atom BIF from Erlang.
% This is the same as `is_atom(foo)` in Erlang.
Erlang.is_atom('foo) % => true
% Accessing the function delete from module lists.
% This is the same as `lists:member(1, [1,2,3])` in Erlang.
Erlang.lists.member(1, [1,2,3]) % => true
As there is no conversion between most Erlang data types and Elixir ones, there is no performance hit in invoking Erlang methods. The only exception are strings that are binaries in Elixir and may need to be converted to char lists in some specific erlang modules. More details were outline in the BitString and String sections above.
Finally, notice that Erlang is not a real object in Elixir, but just a proxy that is converted to erlang calls at compile time.
List comprehensions allow you to quickly build a list from another list:
[n*2 for n in [1,2,3,4]] % => [2,4,6,8]
The comprehension is defined with the for keyword which accepts several expressions. Those expressions can be generators, as in x in [1,2,3,4], or filters:
% A comprehension with a generator and a filter
[n for n in [1,2,3,4,5,6], X rem 2 == 0] % => [2,4,6]
% A comprehension with two generators
[x*y for x in [1,2], y in [2,3]] % => [2,3,4,6]
There are two types of generators in Elixir/Erlang: list and bit string generator:
% A list generator:
[n*2 for n in [1,2,3,4]] % => [2,4,6,8]
% A bit string generator:
[n*2 for <<n>> in <<1,2,3,4>>] % => [2,4,6,8]
Bit string generators are quite useful when you need to organize bit string streams:
pixels = <<213,45,132,64,76,32,76,0,0,234,32,15>>
[{r,g,b} for <<r:8,g:8,b:8>> in pixels ] % => [{213,45,132},{64,76,32},{76,0,0},{234,32,15}]
Remember, as strings are binaries and a binary is a special kind of bit string where the number of bit is a multiple of 8, we can also use strings on comprehensions. For instance, the example below removes all white space characters from a string:
<<c for <<c>> in " hello world ", c != $\s>> % => "helloworld"
Elixir does its best to hide the differences between list and bit string generators from you. However, there is a special case due to Erlang limitation that you need to explicitly tell Erlang that a list is being given as argument:
% This will fail because when Elixir sees that the left side
% of the in expression is a bit string, it expects the right side
% to be a bit string as well:
[n*2 for <<n>> in [<<1>>,<<2>>,<<3>>] % => [2,4,6]
% You need to be explicit and use inlist:
[n*2 for <<n>> inlist [<<1>>,<<2>>,<<3>>] % => [2,4,6]
% inbin is also available:
[n*2 for <<n>> inbin <<1,2,3>>] % => [2,4,6]
You can read more about list and bit string comprehensions in Learn You Some Erlang.
This section will discuss Elixir's Object Model. Its main aspects are:
- Dynamic Dispatch - when a method is invoked on an object, the object itself determines which code gets executed
- Mixins - an object does not contain methods, all methods are packed into modules that are mixed into objects
- Encapsulation - methods can either be public or private
- Open recursion - Elixir's has a special variable called
selfthat allows a method body to invoke another method body of the same object, passing through the ancestors chain - Reflections - Elixir is able to observe and modify an object structure at runtime
Elixir's Object Model focuses on method dispatching. Imagine you have a Person structure with fields name and age generated by an ORM. Retrieving this Person structure, changing its name and saving it would be as follow in Erlang:
Person = person:find(john),
Modified = person:set(name, john_doe, Person)
true = person:save(Modified)
In Elixir, this would be written as:
person = Person.find('john)
modified = person.set('name, 'john_doe)
true = modified.save
In Erlang, every time we want to do something with the Person structure, we need to explicitly call the module person and pass the Person structure as parameter.
Elixir is more concise due to method dispatching. Once you create a person object, you can invoke methods on it directly and there isn't a need to always pass the own list object as argument. The need for dynamic method dispatching is one of the main reasons for the existence of Elixir and its Object Model.
In Elixir, everything is an object. Objects carry properties, they don't carry methods. We can define a new object as follow:
% Define an object Person
object Person
end
% Creates an instance of this object
Person.new
In Elixir, modules carry behavior, i.e. methods. All modules are objects, but not all objects are modules. We can define a new module Speak with a method called say that receives a message and prints it out as follow:
module Speak
def say(message)
IO.puts message
end
end
The convenience of objects comes when we add modules to objects:
person = Person.new
person.say "Hi" % => Raises no method error
another_person = Person.new.mixin(Speak)
another_person.say "Hi" % => "Hi"
The mixin method adds the given module to the current object mixins chain. Therefore, every time we invoke a method in this object, it will search if the method exists in one of its mixins. We can retrieve all mixins of an object with the method __mixins__:
another_person.__mixins__ % => ['Speak, 'Object::Methods]
The Speak module is the one we added and Object::Methods is a module included by default in all objects and is where the __mixins__ method is implemented.
If every time we create a new Person instance, we need to explicitly mix in a module, Elixir wouldn't be much useful. For this reason, we define in the object Person that all of its children has a Speak module by default. This can be done with the proto method:
object Person
proto Speak
end
Person.new.say "Hi" % => "Hi"
Person.__protos__ % => ['Speak, 'Object::Methods]
Person.new.__mixins__ % => ['Speak, 'Object::Methods]
A proto is how an object specifies how its children is going to behave. In other words, a proto added to the parent, becomes a mixin to the child.
Since everything is an object, the mixin method we discussed earlier is also available to the Person object:
module NewBorns
def create_and_cry
instance = self.new
instance.say "whaaaaaaa"
instance
end
end
object Person
mixin NewBorns
proto Speak
end
person = Person.create_and_cry % => "whaaaaaaa"
Person.__mixins__ % => ['NewBorns, 'Object::Methods]
Person.__protos__ % => ['Speak, 'Object::Methods]
This wraps the core of Elixir object system. Remember: everything is an object, methods are defined in modules and modules can be either mixed into objects (mixin), changing their current behavior, or added as prototype (proto), which will define the behavior of all children of that object. Finally, all modules defined as proto in the parent, becomes a mixin to the child.
On top of that, Elixir provides a better way to organize our code. Let's rewrite our Person object:
object Person
module Mixin
def create_and_cry
instance = self.new
instance.say "whaaaaaaa"
instance
end
end
module Proto
def say(message)
IO.puts message
end
end
mixin Person::Mixin
proto Person::Proto
end
Instead of defining modules without a namespace, we can define them inside the Person object, avoiding polluting the main namespace and reducing the chance of conflicts.
Finally, since the pattern above is very common, Elixir provides three conveniences to make our code more expressive:
- If a module
Mixinis defined inside an object, it is automatically added asmixin; - If a module
Protois defined inside an object, it is automatically added asproto; - You can also completely skip the
protomodule and define methods as if you were defining methods inside the object. This is a just a syntax convenience. Internally, Elixir will still create aProtomodule and automatically add it asprototo your object.
With these conveniences in mind, let's rewrite our Person object once again:
object Person
module Mixin
def create_and_cry
instance = self.new
instance.say "whaaaaaaa"
instance
end
end
def say(message)
IO.puts message
end
end
This is much better! Now let's prove that everything is the same as before:
Person.__mixins__ % => ['Person::Mixin, 'Object::Methods]
Person.__protos__ % => ['Person::Proto, 'Object::Methods]
When creating an object, we sometimes want to define properties specific to that object. For example, a Person may have name and age as properties. This can be done by defining such properties as instance variables in the initialize:
object Person
def initialize(name, age)
% Return a new version of this object but
% with name and age as instance variables
@('name: name, 'age: age)
end
def name
@name
end
def age
@age
end
end
person = Person.new('john, 24)
person.name % => 'john
person.age % => 24
Notice the initialize method needs to return an object of the same kind as the one being initialized. The @() syntax used above is just a special syntax to the set_ivars method. Both formats accept a dict and can be used in any method:
object Person
def initialize(name, age)
@('name: name, 'age: age)
end
def name
@name
end
def age
@age
end
def name(value)
@('name: value)
end
end
person = Person.new('john, 24)
another_person = person.name('john_doe)
person.name % => 'john
person.age % => 24
another_person.name % => 'johh_doe
another_person.age % => 24
Notice that @() (and set_ivars) returns a new object. This is expected because as Erlang structures are immutable, all objects in Elixir are also immutable. Above we can see that the initial person object has not changed at all.
One final note about the object model is how instantiation works. When you create an instance from Person, it annotates that the parent for that instance is the Person object. Let's take a look at it:
person = Person.new
person.__parent__ % => Person
The Person object is a direct child from Object:
Person.__parent__ % => Object
While all modules are children from Module which is a child from Object. The object Object, has no parent:
Person::Mixin.__parent__ % => Module
Person::Proto.__parent__ % => Module
Module.__parent__ % => Object
Object.__parent__ % => []
The object Object defines Object::Methods as proto, this is why all objects have this method as their mixin. It doesn't matter if you are a child, a grandchild or a grand-grandchild from Object, this mixin will be available to you. This happens because, in order to calculate all mixins for a given object, Elixir traverses the whole ancestors chain getting all modules defined as proto for all parents.
The Object Graph for all these objects can be seen below:
--------------- Parent -----------------
| Object | <---------- | Module | <---
--------------- ----------------- |
^ ^ |
| Parent | Parent |
| | |
--------------- mixin ----------------- |
| Person | <---------- | Person::Mixin | | Parent
--------------- _ ----------------- |
^ |\__ proto |
| Parent \___ |
| \__ |
--------------- \----------------- |
| Person.new | <---------- | Person::Proto | ---|
--------------- mixin -----------------
Once again, remember:
- Everything is an object;
- Methods are defined in modules. All modules are objects, but not all objects are modules. Besides, modules cannot have instances.
Person::MixinandPerson::Protodefined above are modules; - Modules can be either mixed into objects (
mixin), changing their current behavior... - Or added as prototype (
proto), which will define the behavior of all children/instances from that object; - Finally, all modules defined as
protoin the parent, becomes amixinto the child.
In the Object Model section, we have discussed modules and methods. Modules are very close to Erlang modules and it is important to keep that in mind if you are coming from a language like Ruby.
In Elixir, there are two ways to call a method. Using self explicitly and without it. Let's see some examples:
module Example
% Call a method defined in Object.
def remote_call
self.__parent__
end
% Calling a method specified in ancestors does not require self.
def implicit_remote_call
__parent__
end
% Call a method defined in this module explicitly.
def local_call
self.remote_call
end
% Call a method defined in this module implicitly.
def implicit_local_call
remote_call
end
end
Local calls are compiled at parse time and are faster than explicit self calls. However, local calls can only be made to methods existing in the current module or its ancestors. That said, imagine we have a module that requires a hook to be implemented in the target object:
module Hooks
def do_something
my_hook
end
end
object Target
proto Hooks
def my_hook
13
end
end
The example above won't compile because my_hook is a local call, but no my_hook method can be found in the module or its ancestors at compile time. Our second attempt could be:
module Hooks
def do_something
my_hook
end
def my_hook
11
end
end
object Target
proto Hooks
def my_hook
13
end
end
Target.new.do_something % => 11
In this case, notice that do_something still returns 11. This is because my_hook inside do_something is a local call. It won't go through the dispatch chain. However, the following works as expected.
module Hooks
def do_something
self.my_hook
end
def my_hook
11
end
end
object Target
proto Hooks
def my_hook
13
end
end
Target.new.do_something % => 13
By using self, we force the method to be dispatched instead of being invoked locally.
In Erlang, it is very important to make a difference between local calls and remote calls, as they affect how hot code swapping works. You can read this section from Learn You Some Erlang for more information.
Elixir keeps the same semantics as Erlang and makes a difference between local and remote calls. A method call is considered local if it is called implicitly and the method invoked is in the same module:
module Example
% Invoke method defined in Object explicitly.
def remote_call
self.__parent__
end
% Invoke method defined in Object implicitly.
def implicit_remote_call
__parent__
end
% This is a local call because internal is defined locally.
def local_call
internal
end
% Even though internal is defined locally, since we use self
% this is not a local call, but a remote call.
def not_a_local_call
self.internal
end
def internal
13
end
end
Finally, notice that if a variable is defined with the same name as method, the variable is given higher preference:
module AnotherExample
def some_value
13
end
def value
some_value = 11
some_value
end
end
AnotherExample.value % => 11
Now that we know the difference between local and remote calls we can take a better look at method visibility. Elixir provides two different visibilities: public and private. All methods are public by default, this means that a method can be called from anywhere, at any time:
module Example
def public_method
13
end
def calling_public_method
public_method
end
def calling_public_method2
self.public_method
end
end
Example.public_method % => 13
Example.calling_public_method % => 13
Example.calling_public_method2 % => 13
Private methods are the ones accessible just through a local call. This means a module cannot access private methods from other modules even after adding them as mixin or as proto.
module Example
def calling_private_method
private_method
end
def calling_private_method2
self.private_method
end
private
def private_method
13
end
end
% Won't work, it is not a local call.
Example.private_method
% It works because calling_private_method is doing a local call.
Example.calling_private_method % => 13
% It won't work because calling_private_method2 is not doing a local call.
Example.calling_private_method2
module Invoker
mixin Example
def calling_private_method
self.private_method
end
end
% It won't work because private_method is only accessible from
% local calls (from the same module it is defined).
Invoker.calling_private_method
In the "Variables and Pattern Matching" section above, we have showed a simple Fibonacci example using Pattern Matching in the method signature. However, that example was not properly optimized:
module Math
def fibonacci(0)
0
end
def fibonacci(1)
1
end
def fibonacci(n)
fibonacci(n - 1) + fibonacci(n - 2)
end
end
As Erlang, Elixir does tail call optimization. We can rewrite the fibonacci method with a version that will use tail call optimization like below:
module OptimizedMath
def fibonacci(n)
fibonacci(n, 1, 0)
end
def fibonacci(0, _, result)
result
end
def fibonacci(n, next, result)
fibonacci(n - 1, next + result, next)
end
end
OptimizedMath.fibonacci(0) % => 0
OptimizedMath.fibonacci(1) % => 1
OptimizedMath.fibonacci(3) % => 2
OptimizedMath.fibonacci(10) % => 55
The third fibonacci method in OptimizedMath is optimized because the last method it calls is itself. In order to understand the difference between both versions and how tail call optimization works, we recommend reading more about it on the Recursion chapter from Learn You Some Erlang.
As we mentioned earlier and saw in the examples above, pattern matching is also allowed in method signatures. If the given args does not match a given method, it will try the next one until it succeeds or none is found, raising an error. Below, is an example that checks if a list is the prefix of another, relying solely on pattern matching:
module Prefix
% This won't match if the first element of each list is not equal
def is?([i|prefix], [i|list])
is?(prefix, list)
end
% If prefix is empty or gets empty, it matches
def is?([], _list)
true
end
% Anything else is false
def is?(_prefix, _list)
false
end
end
The fact OrderedDicts are allowed in pattern matching and pattern matching is allowed in methods, makes it possible to use key-value arguments:
def do_something(value, 'special: true)
% Do something special
end
def do_something(value, 'special: false)
% Do something not that special
end
Besides supporting pattern matching in methods, Elixir also supports default arguments. You can specify a default argument using the := operator. Example:
module Default
def sum(a := 1, b := 2)
a + b
end
end
Default.sum % => 3
Default.sum(2) % => 4
Default.sum(2, 3) % => 5
Default arguments working by implicitly defining methods that accepts less arguments. The code above generates exactly the same module as follow:
module Default
def sum()
sum(1, 2)
end
def sum(a)
sum(a, 2)
end
def sum(a := 1, b := 2)
a + b
end
end
Before proceeding on how to retrieve a method as a function, it is important to notice that, as in Erlang, Elixir's methods are identified by its name and arity. Therefore, the OptimizedMath module above has only two methods: a fibonacci with arity 1 and fibonnaci with arity 3. If two methods are defined with same name and arity, they become different clauses for the same method and pattern matching is used in order to specify which method to call. That said, the Math module has only one fibonnaci method with arity equals to 1 and 3 clauses.
Remaining of this section still needs to be implemented and written.
Loading code in Elixir happens by automatically loading modules inside the compilation directory. For instance, if you are building a library and have the compiled code inside the exbin/ directory, you can access any of the modules in it using:
bin/elixir -pa exbin/ -e "SomeCompiledModule.method"
You can find more documentation by typing "bin/elixir". You may also add and remove paths programatically
When scripting, it may be convenient to load another specific script file, you can do that using Code.load_file or Code.require_file in which the second assures the file is being loaded just once.
Elixir provides the same facilities to deal with processes as Erlang. Messages are sent using <- and the same receive/after syntax is available. You can learn more about it by checking the process.ex file in the examples folder: https://github.com/josevalim/elixir/tree/master/examples/process.ex
Besides, Elixir also imports behaviors from Erlang OTP. Currently, just GenServer is implemented and support for others will come as needed. Once again, you can learn more in the examples folder: https://github.com/josevalim/elixir/tree/master/examples/gen_server.ex
- https://github.com/josevalim/elixir/tree/master/lib/process.ex
- https://github.com/josevalim/elixir/tree/master/lib/gen_server.ex
Some advanced topics related to Elixir.
As explained at the beginning of this README, Elixir allows the same variable to be assigned more than once. However, keep in mind that variables assignment inside functions do not change the original binding. For example:
a = 1
b = -> a = 2
b()
a % => 1
As everything is immutable, when the function assigns a new variable, it creates a new binding with the new variable value and the original binding is never modified. This is important to avoid side-effects when passing functions to different processes (parallel execution).
Also, Elixir has much more flexible rules when it comes to variables inside control-flow expressions. For instance, the following works:
x = 1
if true
x = 2
end
x % => 2
The same is also true for receive/after and case/match expressions. The only exception comes to try/catch scenarios, where a variable defined inside such blocks is never accessible from the outside. For example:
x = 1
try
x = 2
catch _:_
% Do nothing
end
x % => 1
Elixir has basic support for guards. They can be used on method declaration, receive/match clauses, case/match clauses and catch clauses. In all cases, they are declared using the keyword when. For instance, you could implement a method that returns the absolute value of a number as follow:
def abs(x) when x < 0
- x
end
def abs(x)
x
end
In a receive/case match clause, we would do instead:
case y
match x when x < 0 then - x
match x then x
end
Finally, in catch expressions it works as follow:
try
throw y
catch 'throw:x when x < 0
- x
catch 'throw:x
x
end
Guards only supports arithmetic operators on numbers, comparison operators and the following boolean operators: or, orelse, and, andalso and not.
Elixir allows you to dynamically dispatch methods:
[1,2,3].send 'head % => 1
{}.send 'empty? % => true
You can also retrieve internal information about objects, like ivars, methods available, mixins, protos, etc:
{}.public_mixin_methods.member? 'empty? % => true
{}.__parent__ % => Hash
Elixir also allows you to dynamically define methods. For example, below we can define attribute readers for both "title" and "author" attributes dynamically:
object Book
def initialize(title, author)
@('title: title, 'author: author)
end
["title", "author"].each do (method)
module_eval __FILE__, __LINE__ + 1, ~~METHOD
def #{method}
@#{method}
end
~~
end
end
The real benefit is when you encapsulate it inside a method. For example, the definition above is inside Elixir, so you can actually call:
object Book
attr_reader ['title, 'author]
def initialize(title, author)
@('title: title, 'author: author)
end
end
Finally, Elixir also has a hook that allows you to dynamically invoke a method when one does not exist. This hook is a method called method_missing and receives a method and a list of parameters as arguments:
object Shouter
% Methods called without arguments will be handled here
def method_missing(method, [])
IO.puts "#{method}!!!"
end
% Call default behavior
def method_missing(method, args)
super method, args
end
end
shouter = Shouter.new
shouter.hello % => "hello!!!"
shouter.bye? % => "bye?!!!"
Notice the example above also calls super which allows you to call the next method with the same name in the mixins chain.
- https://github.com/josevalim/elixir/tree/master/lib/object.ex
- https://github.com/josevalim/elixir/tree/master/lib/module.ex
The focus in Elixir so far has not been in performance, but there are a few things you can do right now.
Elixir can compile to native code using the Hipe compiler. All you need to do is to export the following before running your code:
export ERL_COMPILER_OPTIONS=native
Elixir allows you to import records from Erlang code. Here is an example that imports the file_info record available in the kernel module:
Code.require "record"
object FileInfo
proto Record
record 'file_info, 'from_lib: "kernel/include/file.hrl"
end
% Manually access the Erlang file:read_file_info method
% passing the current file as a char list.
{ 'ok, info } = Erlang.file.read_file_info(__FILE__.to_char_list)
% Create a new FileInfo object based on the tuple returned above
record = FileInfo.new info
% Profit by accessing the record info
record.access % => 'read_write
Copyright (c) 2011 José Valim
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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