| language | contributors | filename | |||
|---|---|---|---|---|---|
elixir |
|
learnelixir.ex |
Elixir is a modern functional language built on top of the Erlang VM. It's fully compatible with Erlang, but features a more standard syntax and many more features.
# Single line comments start with a number symbol.
# There's no multi-line comment,
# but you can stack multiple comments.
# To use the elixir shell use the `iex` command.
# Compile your modules with the `elixirc` command.
# Both should be in your path if you installed elixir correctly.
## ---------------------------
## -- Basic types
## ---------------------------
# There are numbers
3 # integer
0x1F # integer
3.0 # float
# Atoms, that are literals, a constant with name. They start with `:`.
:hello # atom
# Tuples that are stored contiguously in memory.
{1,2,3} # tuple
# We can access a tuple element with the `elem` function:
elem({1, 2, 3}, 0) #=> 1
# Lists that are implemented as linked lists.
[1,2,3] # list
# We can access the head and tail of a list as follows:
[head | tail] = [1,2,3]
head #=> 1
tail #=> [2,3]
# In elixir, just like in Erlang, the `=` denotes pattern matching and
# not an assignment.
#
# This means that the left-hand side (pattern) is matched against a
# right-hand side.
#
# This is how the above example of accessing the head and tail of a list works.
# A pattern match will error when the sides don't match, in this example
# the tuples have different sizes.
# {a, b, c} = {1, 2} #=> ** (MatchError) no match of right hand side value: {1,2}
# There's also binaries
<<1,2,3>> # binary
# Strings and char lists
"hello" # string
'hello' # char list
# Multi-line strings
"""
I'm a multi-line
string.
"""
#=> "I'm a multi-line\nstring.\n"
# Strings are all encoded in UTF-8:
"héllò" #=> "héllò"
# Strings are really just binaries, and char lists are just lists.
<<?a, ?b, ?c>> #=> "abc"
[?a, ?b, ?c] #=> 'abc'
# `?a` in elixir returns the ASCII integer for the letter `a`
?a #=> 97
# To concatenate lists use `++`, for binaries use `<>`
[1,2,3] ++ [4,5] #=> [1,2,3,4,5]
'hello ' ++ 'world' #=> 'hello world'
<<1,2,3>> <> <<4,5>> #=> <<1,2,3,4,5>>
"hello " <> "world" #=> "hello world"
## ---------------------------
## -- Operators
## ---------------------------
# Some math
1 + 1 #=> 2
10 - 5 #=> 5
5 * 2 #=> 10
10 / 2 #=> 5.0
# In elixir the operator `/` always returns a float.
# To do integer division use `div`
div(10, 2) #=> 5
# To get the division remainder use `rem`
rem(10, 3) #=> 1
# There's also boolean operators: `or`, `and` and `not`.
# These operators expect a boolean as their first argument.
true and true #=> true
false or true #=> true
# 1 and true #=> ** (ArgumentError) argument error
# Elixir also provides `||`, `&&` and `!` which accept arguments of any type.
# All values except `false` and `nil` will evaluate to true.
1 || true #=> 1
false && 1 #=> false
nil && 20 #=> nil
!true #=> false
# For comparisons we have: `==`, `!=`, `===`, `!==`, `<=`, `>=`, `<` and `>`
1 == 1 #=> true
1 != 1 #=> false
1 < 2 #=> true
# `===` and `!==` are more strict when comparing integers and floats:
1 == 1.0 #=> true
1 === 1.0 #=> false
# We can also compare two different data types:
1 < :hello #=> true
# The overall sorting order is defined below:
# number < atom < reference < functions < port < pid < tuple < list < bit string
# To quote Joe Armstrong on this: "The actual order is not important,
# but that a total ordering is well defined is important."
## ---------------------------
## -- Control Flow
## ---------------------------
# `if` expression
if false do
"This will never be seen"
else
"This will"
end
# There's also `unless`
unless true do
"This will never be seen"
else
"This will"
end
# Remember pattern matching? Many control-flow structures in elixir rely on it.
# `case` allows us to compare a value against many patterns:
case {:one, :two} do
{:four, :five} ->
"This won't match"
{:one, x} ->
"This will match and assign `x` to `:two`"
_ ->
"This will match any value"
end
# It's common practice to assign a value to `_` if we don't need it.
# For example, if only the head of a list matters to us:
[head | _] = [1,2,3]
head #=> 1
# For better readability we can do the following:
[head | _tail] = [:a, :b, :c]
head #=> :a
# `cond` lets us check for many conditions at the same time.
# Use `cond` instead of nesting many `if` expressions.
cond do
1 + 1 == 3 ->
"I will never be seen"
2 * 5 == 12 ->
"Me neither"
1 + 2 == 3 ->
"But I will"
end
# It is common to see a last condition equal to `true`, which will always match.
cond do
1 + 1 == 3 ->
"I will never be seen"
2 * 5 == 12 ->
"Me neither"
true ->
"But I will (this is essentially an else)"
end
# `try/catch` is used to catch values that are thrown, it also supports an
# `after` clause that is invoked whether or not a value is caught.
try do
throw(:hello)
catch
message -> "Got #{message}."
after
IO.puts("I'm the after clause.")
end
#=> I'm the after clause
# "Got :hello"
## ---------------------------
## -- Modules and Functions
## ---------------------------
# Anonymous functions (notice the dot)
square = fn(x) -> x * x end
square.(5) #=> 25
# They also accept many clauses and guards.
# Guards let you fine tune pattern matching,
# they are indicated by the `when` keyword:
f = fn
x, y when x > 0 -> x + y
x, y -> x * y
end
f.(1, 3) #=> 4
f.(-1, 3) #=> -3
# Elixir also provides many built-in functions.
# These are available in the current scope.
is_number(10) #=> true
is_list("hello") #=> false
elem({1,2,3}, 0) #=> 1
# You can group several functions into a module. Inside a module use `def`
# to define your functions.
defmodule Math do
def sum(a, b) do
a + b
end
def square(x) do
x * x
end
end
Math.sum(1, 2) #=> 3
Math.square(3) #=> 9
# To compile our simple Math module save it as `math.ex` and use `elixirc`
# in your terminal: elixirc math.ex
# Inside a module we can define functions with `def` and private functions with `defp`.
# A function defined with `def` is available to be invoked from other modules,
# a private function can only be invoked locally.
defmodule PrivateMath do
def sum(a, b) do
do_sum(a, b)
end
defp do_sum(a, b) do
a + b
end
end
PrivateMath.sum(1, 2) #=> 3
# PrivateMath.do_sum(1, 2) #=> ** (UndefinedFunctionError)
# Function declarations also support guards and multiple clauses:
defmodule Geometry do
def area({:rectangle, w, h}) do
w * h
end
def area({:circle, r}) when is_number(r) do
3.14 * r * r
end
end
Geometry.area({:rectangle, 2, 3}) #=> 6
Geometry.area({:circle, 3}) #=> 28.25999999999999801048
# Geometry.area({:circle, "not_a_number"})
#=> ** (FunctionClauseError) no function clause matching in Geometry.area/1
# Due to immutability, recursion is a big part of elixir
defmodule Recursion do
def sum_list([head | tail], acc) do
sum_list(tail, acc + head)
end
def sum_list([], acc) do
acc
end
end
Recursion.sum_list([1,2,3], 0) #=> 6
# Elixir modules support attributes, there are built-in attributes and you
# may also add custom attributes.
defmodule MyMod do
@moduledoc """
This is a built-in attribute on a example module.
"""
@my_data 100 # This is a custom attribute.
IO.inspect(@my_data) #=> 100
end
## ---------------------------
## -- Records and Exceptions
## ---------------------------
# Records are basically structures that allow you to associate a name with
# a particular value.
defrecord Person, name: nil, age: 0, height: 0
joe_info = Person.new(name: "Joe", age: 30, height: 180)
#=> Person[name: "Joe", age: 30, height: 180]
# Access the value of name
joe_info.name #=> "Joe"
# Update the value of age
joe_info = joe_info.age(31) #=> Person[name: "Joe", age: 31, height: 180]
# The `try` block with the `rescue` keyword is used to handle exceptions
try do
raise "some error"
rescue
RuntimeError -> "rescued a runtime error"
_error -> "this will rescue any error"
end
# All exceptions have a message
try do
raise "some error"
rescue
x in [RuntimeError] ->
x.message
end
## ---------------------------
## -- Concurrency
## ---------------------------
# Elixir relies on the actor model for concurrency. All we need to write
# concurrent programs in elixir are three primitives: spawning processes,
# sending messages and receiving messages.
# To start a new process we use the `spawn` function, which takes a function
# as argument.
f = fn -> 2 * 2 end #=> #Function<erl_eval.20.80484245>
spawn(f) #=> #PID<0.40.0>
# `spawn` returns a pid (process identifier), you can use this pid to send
# messages to the process. To do message passing we use the `send` operator.
# For all of this to be useful we need to be able to receive messages. This is
# achived with the `receive` mechanism:
defmodule Geometry do
def area_loop do
receive do
{:rectangle, w, h} ->
IO.puts("Area = #{w * h}")
area_loop()
{:circle, r} ->
IO.puts("Area = #{3.14 * r * r}")
area_loop()
end
end
end
# Compile the module and create a process that evaluates `area_loop` in the shell
pid = spawn(fn -> Geometry.area_loop() end) #=> #PID<0.40.0>
# Send a message to `pid` that will match a pattern in the receive statement
send pid, {:rectangle, 2, 3}
#=> Area = 6
# {:rectangle,2,3}
send pid, {:circle, 2}
#=> Area = 12.56000000000000049738
# {:circle,2}
# The shell is also a process, you can use `self` to get the current pid
self() #=> #PID<0.27.0>- Getting started guide from elixir webpage
- Elixir Documentation
- "Learn You Some Erlang for Great Good!" by Fred Hebert
- "Programming Erlang: Software for a Concurrent World" by Joe Armstrong