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diff --git a/elixir.html.markdown b/elixir.html.markdown new file mode 100644 index 00000000..8ea499ff --- /dev/null +++ b/elixir.html.markdown @@ -0,0 +1,398 @@ +--- +language: elixir +contributors: + - ["Joao Marques", "http://github.com/mrshankly"] +filename: 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. + +```ruby + +# Single line comments start with a hashtag. + +# 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 catched. +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 `<-` 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 +pid <- {:rectangle, 2, 3} +#=> Area = 6 +# {:rectangle,2,3} + +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> +``` + +## References + +* [Getting started guide](http://elixir-lang.org/getting_started/1.html) from [elixir webpage](http://elixir-lang.org) +* [Elixir Documentation](http://elixir-lang.org/docs/master/) +* ["Learn You Some Erlang for Great Good!"](http://learnyousomeerlang.com/) by Fred Hebert +* "Programming Erlang: Software for a Concurrent World" by Joe Armstrong |