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| -rw-r--r-- | elixir.html.markdown | 179 |
1 files changed, 125 insertions, 54 deletions
diff --git a/elixir.html.markdown b/elixir.html.markdown index a37d0f5e..11a0701c 100644 --- a/elixir.html.markdown +++ b/elixir.html.markdown @@ -24,15 +24,15 @@ filename: learnelixir.ex {1,2,3} # tuple # We can access a tuple element with the `elem` function: -elem({1, 2, 3}, 0) # => 1 +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] +head #=> 1 +tail #=> [2,3] # In elixir, just like in erlang, the `=` denotes pattern matching and # not an assignment. @@ -44,7 +44,7 @@ tail # => [2,3] # 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} +{a, b, c} = {1, 2} #=> ** (MatchError) no match of right hand side value: {1,2} # There's also binaries <<1,2,3>> # binary @@ -53,64 +53,73 @@ tail # => [2,3] "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" +"héllò" #=> "héllò" # Strings are really just binaries, and char lists are just lists. -<<?a, ?b, ?c>> # => "abc" -[?a, ?b, ?c] # => 'abc' +<<?a, ?b, ?c>> #=> "abc" +[?a, ?b, ?c] #=> 'abc' # `?a` in elixir returns the ASCII integer for the letter `a` -?a # => 97 +?a #=> 97 + +# To concatenate lists use `++`, for binaries use `<>` +[1,2,3] ++ [4,5] #=> [1,2,3,4,5] +'hello ' ++ 'world' #=> 'hello world' -## TODO: -###################################################### -## JOIN BINARIES AND LISTS -###################################################### +<<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 +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 +div(10, 2) #=> 5 # To get the division remainder use `rem` -rem(10, 3) # => 1 +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 +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 +1 || true #=> 1 +false && 1 #=> false +nil && 20 #=> nil -!true # => false +!true #=> false # For comparisons we have: `==`, `!=`, `===`, `!==`, `<=`, `>=`, `<` and `>` -1 == 1 # => true -1 != 1 # => false -1 < 2 # => true +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 +1 == 1.0 #=> true +1 === 1.0 #=> false # We can also compare two different data types: -1 < :hello # => true +1 < :hello #=> true # The overall sorting order is defined below: number < atom < reference < functions < port < pid < tuple < list < bit string @@ -151,11 +160,11 @@ end # It's common practive 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 +head #=> 1 # For better readability we can do the following: [head | _tail] = [:a, :b, :c] -head # => :a +head #=> :a # `cond` lets us check for many conditions at the same time. # Use `cond` instead of nesting many `if` expressions. @@ -187,27 +196,19 @@ catch after IO.puts("I'm the after clause.") end -# => I'm the after clause -# "Got :hello" - -## TODO: -###################################################### -## GUARDS -###################################################### +#=> I'm the after clause +# "Got :hello" ## --------------------------- ## -- Modules and Functions ## --------------------------- -############################### -## EXPLAIN built-in functions? -############################### - # Anonymous functions (notice the dot) square = fn(x) -> x * x end square.(5) #=> 25 -# They also accept many clauses and guards +# 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 @@ -216,6 +217,12 @@ 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 @@ -234,9 +241,7 @@ Match.square(3) #=> 9 # To compile our little Math module save it as `math.ex` and use `elixirc` elixirc math.ex -# Inside a module we can define functions with `def` and -# private functions with `defp`. -# +# 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 @@ -258,7 +263,7 @@ defmodule Geometry do w * h end - def area({:circle, r}) when r > 0 do + def area({:circle, r}) when is_number(r) do 3.14 * r * r end end @@ -279,9 +284,17 @@ end Recursion.sum_list([1,2,3], 0) #=> 6 -############################### -## EXPLAIN module attributes -############################### +# 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 @@ -300,11 +313,69 @@ joe_info.name #=> "Joe" # Update the value of age joe_info = joe_info.age(31) #=> Person[name: "Joe", age: 31, height: 180] -## TODO: Exceptions +# 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 ## --------------------------- -## TODO +# 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} ``` + +## 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
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