Elixir Language #elixir Table of Contents About Chapter 1: Getting started with Elixir Language Remarks Versions Examples Hello World Hello World from IEx Chapter 2: Basic .gitignore for elixir program Chapter 3: Basic .gitignore for elixir program Remarks Examples A basic .gitignore for Elixir Example Standalone elixir application Phoenix application Auto-generated .gitignore Chapter 4: basic use of guard clauses Examples basic uses of guard clauses Chapter 5: BEAM Examples Introduction Chapter 6: Behaviours Examples Introduction Chapter 7: Better debugging with IO.inspect and labels Introduction Remarks Examples Without labels 1 2 2 2 2 2 3 5 6 6 6 6 6 6 7 7 8 8 8 10 10 10 11 11 11 12 12 12 12 12 With labels Chapter 8: Built-in types Examples Numbers Atoms Binaries and Bitstrings Chapter 9: Conditionals Remarks Examples case if and unless cond with clause Chapter 10: Constants Remarks Examples Module-scoped constants Constants as functions Constants via macros Chapter 11: Data Structures Syntax Remarks Examples Lists Tuples Chapter 12: Debugging Tips Examples Debugging with IEX.pry/0 Debugging with IO.inspect/1 Debug in pipe Pry in pipe Chapter 13: Doctests 13 14 14 14 15 15 17 17 17 17 17 18 18 20 20 20 20 20 21 23 23 23 23 23 23 24 24 24 24 25 25 27 Examples Introduction Generating HTML documentation based on doctest Multiline doctests Chapter 14: Ecto Examples Adding a Ecto.Repo in an elixir program "and" clause in a Repo.get_by/3 Querying with dynamic fields Add custom data types to migration and to schema Chapter 15: Erlang Examples Using Erlang Inspect an Erlang module Chapter 16: ExDoc Examples Introduction Chapter 17: ExUnit Examples Asserting Exceptions Chapter 18: Functional programming in Elixir Introduction Examples Map Reduce Chapter 19: Functions Examples Anonymous Functions Using the capture operator Multiple bodies Keyword lists as function parameters 27 27 27 27 29 29 29 29 30 30 31 31 31 31 32 32 32 33 33 33 34 34 34 34 34 36 36 36 36 37 37 Named Functions & Private Functions Pattern Matching Guard clauses Default Parameters Capture functions Chapter 20: Getting help in IEx console Introduction Examples Listing Elixir modules and functions Chapter 21: IEx Console Tips & Tricks Examples Recompile project with `recompile` See documentation with `h` Get value from last command with `v` Get the value of a previous command with `v` Exit IEx console See information with `i` Creating PID Have your aliases ready when you start IEx Persistent history When Elixir console is stuck... break out of incomplete expression Load a module or script into the IEx session Chapter 22: Installation Examples Fedora Installation OSX Installation Homebrew Macports Debian/Ubuntu Installation Gentoo/Funtoo Installation Chapter 23: Join Strings 37 38 38 39 39 41 41 41 41 42 42 42 42 42 42 43 43 44 44 44 44 45 46 47 47 47 47 47 47 47 47 49 Examples Using String Interpolation Using IO List Using Enum.join Chapter 24: Lists Syntax Examples Keyword Lists Char Lists Cons Cells Mapping Lists List Comprehensions Combined example Summary List difference List Membership Converting Lists to a Map Chapter 25: Maps and Keyword Lists Syntax Remarks Examples Creating a Map Creating a Keyword List Difference between Maps and Keyword Lists Chapter 26: Metaprogramming Examples Generate tests at compile time Chapter 27: Mix Examples Create a Custom Mix Task Custom mix task with command line arguments Aliases 49 49 49 49 50 50 50 50 51 52 52 53 53 53 54 54 54 55 55 55 55 55 55 56 57 57 57 58 58 58 58 58 Get help on available mix tasks Chapter 28: Modules Remarks Module Names Examples List a module's functions or macros Using modules Delegating functions to another module Chapter 29: Nodes Examples List all visible nodes in the system Connecting nodes on the same machine Connecting nodes on different machines Chapter 30: Operators Examples The Pipe Operator Pipe operator and parentheses Boolean operators Comparison operators Join operators 'In' operator Chapter 31: Optimization Examples Always measure first! Chapter 32: Pattern matching Examples Pattern matching functions Pattern matching on a map Pattern matching on a list Get the sum of a list using pattern matching Anonymous functions Tuples 59 60 60 60 60 60 60 61 62 62 62 62 62 64 64 64 64 65 66 66 67 68 68 68 69 69 69 69 69 70 70 71 Reading a File Pattern matching anonymous functions Chapter 33: Polymorphism in Elixir Introduction Remarks Examples Polymorphism with Protocols Chapter 34: Processes Examples Spawning a Simple Process Sending and Receiving Messages Recursion and Receive Chapter 35: Protocols Remarks Examples Introduction Chapter 36: Sigils Examples Build a list of strings Build a list of atoms Custom sigils Chapter 37: State Handling in Elixir Examples Managing a piece of state with an Agent Chapter 38: Stream Remarks Examples Chaining multiple operations Chapter 39: Strings Remarks Examples 71 71 73 73 73 73 73 75 75 75 75 75 77 77 77 77 78 78 78 78 78 79 79 79 80 80 80 80 81 81 81 Convert to string Get a substring Split a string String Interpolation Check if String contains Substring Join Strings Chapter 40: Task Syntax Parameters Examples Doing work in the background Parallel processing Chapter 41: Tips and Tricks Introduction Examples Creating Custom Sigils and Documenting Multiple [ OR ] iex Custom Configuration - iex Decoration Credits 81 81 81 81 81 82 83 83 83 83 83 83 84 84 84 84 84 84 86 About You can share this PDF with anyone you feel could benefit from it, downloaded the latest version from: elixir-language It is an unofficial and free Elixir Language ebook created for educational purposes. All the content is extracted from Stack Overflow Documentation, which is written by many hardworking individuals at Stack Overflow. It is neither affiliated with Stack Overflow nor official Elixir Language. The content is released under Creative Commons BY-SA, and the list of contributors to each chapter are provided in the credits section at the end of this book. Images may be copyright of their respective owners unless otherwise specified. All trademarks and registered trademarks are the property of their respective company owners. Use the content presented in this book at your own risk; it is not guaranteed to be correct nor accurate, please send your feedback and corrections to info@zzzprojects.com https://riptutorial.com/ 1 Chapter 1: Getting started with Elixir Language Remarks Elixir is a dynamic, functional language designed for building scalable and maintainable applications. Elixir leverages the Erlang VM, known for running low-latency, distributed and fault-tolerant systems, while also being successfully used in web development and the embedded software domain. Versions Version Release Date 0.9 1.0 1.1 1.2 1.3 1.4 2013-05-23 2014-09-18 2015-09-28 2016-01-03 2016-06-21 2017-01-05 Examples Hello World For installation instructions on elixir check here, it describes instructions related to different platforms. Elixir is a programming language that is created using erlang, and uses erlang's BEAM runtime (like JVM for java). We can use elixir in two modes: interactive shell iex or directly running using elixir command. Place the following in a file named hello.exs: IO.puts "Hello world!" https://riptutorial.com/ 2 From the command line, type the following command to execute the Elixir source file: $ elixir hello.exs This should output: Hello world! This is known as the scripted mode of Elixir. In fact, Elixir programs can also be compiled (and generally, they are) into bytecode for the BEAM virtual machine. You can also use iex for interactive elixir shell (recommended), run the command you will get a prompt like this: Interactive Elixir (1.3.4) - press Ctrl+C to exit (type h() ENTER for help) iex(1)> Here you can try your elixir hello world examples: iex(1)> IO.puts "hello, world" hello, world :ok iex(2)> You can also compile and run your modules through iex. For example, if you have a helloworld.ex that contains: defmodule Hello do def sample do IO.puts "Hello World!" end end Through iex, do: iex(1)> c("helloworld.ex") [Hello] iex(2)> Hello.sample Hello World! Hello World from IEx You can also use the IEx (Interactive Elixir) shell to evaluate expressions and execute code. If you are on Linux or Mac, just type iex on your bash and press enter: $ iex If you are on a Windows machine, type: https://riptutorial.com/ 3 C:\ iex.bat Then you will enter into the IEx REPL (Read, Evaluate, Print, Loop), and you can just type something like: iex(1)> "Hello World" "Hello World" If you want to load a script while opening an IEx REPL, you can do this: $ iex script.exs Given script.exs is your script. You can now call functions from the script in the console. Read Getting started with Elixir Language online: https://riptutorial.com/elixir/topic/954/getting- started-with-elixir-language https://riptutorial.com/ 4 Chapter 2: Basic .gitignore for elixir program Read Basic .gitignore for elixir program online: https://riptutorial.com/elixir/topic/6493/basic-- gitignore-for-elixir-program https://riptutorial.com/ 5 Chapter 3: Basic .gitignore for elixir program Remarks Note that the /rel folder may not be needed in your .gitignore file. This is generated if you are using a release management tool such as exrm Examples A basic .gitignore for Elixir /_build /cover /deps erl_crash.dump *.ez # Common additions for various operating systems: # MacOS .DS_Store # Common additions for various editors: # JetBrains IDEA, IntelliJ, PyCharm, RubyMine etc. .idea Example ### Elixir ### /_build /cover /deps erl_crash.dump *.ez ### Erlang ### .eunit deps *.beam *.plt ebin rel/example_project .concrete/DEV_MODE .rebar Standalone elixir application /_build /cover /deps erl_crash.dump *.ez https://riptutorial.com/ 6 /rel Phoenix application /_build /db /deps /*.ez erl_crash.dump /node_modules /priv/static/ /config/prod.secret.exs /rel Auto-generated .gitignore By default, mix new will generate a .gitignore file in the project root that is suitable for Elixir. # The directory Mix will write compiled artifacts to. /_build # If you run "mix test --cover", coverage assets end up here. /cover # The directory Mix downloads your dependencies sources to. /deps # Where 3rd-party dependencies like ExDoc output generated docs. /doc # If the VM crashes, it generates a dump, let's ignore it too. erl_crash.dump # Also ignore archive artifacts (built via "mix archive.build"). *.ez Read Basic .gitignore for elixir program online: https://riptutorial.com/elixir/topic/6526/basic-- gitignore-for-elixir-program https://riptutorial.com/ 7 Chapter 4: basic use of guard clauses Examples basic uses of guard clauses In Elixir, one can create multiple implementations of a function with the same name, and specify rules which will be applied to the parameters of the function before calling the function in order to determine which implementation to run. These rules are marked by the keyword when, and they go between the def function_name(params) and the do in the function definition. A trivial example: defmodule Math do def is_even(num) when num === 1 do false end def is_even(num) when num === 2 do true end def is_odd(num) when num === 1 do true end def is_odd(num) when num === 2 do false end end Say I run Math.is_even(2) with this example. There are two implementations of is_even, with differing guard clauses. The system will look at them in order, and run the first implementation where the parameters satisfy the guard clause. The first one specifies that num === 1 which is not true, so it moves on to the next one. The second one specifies that num === 2, which is true, so this is the implementation that is used, and the return value will be true. What if I run Math.is_odd(1)? The system looks at the first implementation, and sees that since num is 1 the guard clause of the first implementation is satisfied. It will then use that implementation and return true, and not bother looking at any other implementations. Guards are limited in the types of operations they can run. The Elixir documentation lists every allowed operation; in a nutshell they allow comparisons, math, binary operations, type-checking (e.g. is_atom), and a handful of small convenience functions (e.g. length). It is possible to define custom guard clauses, but it requires creating macros and is best left for a more advanced guide. Note that guards do not throw errors; they are treated as normal failures of the guard clause, and the system moves on to look at the next implementation. If you find that you're getting (FunctionClauseError) no function clause matching when calling a guarded function with params https://riptutorial.com/ 8 you expect to work, it may be that a guard clause which you expect to work is throwing an error which is being swallowed up. To see this for yourself, create and then call a function with a guard which makes no sense, such as this which tries to divide by zero: defmodule BadMath do def divide(a) when a / 0 === :foo do :bar end end Calling BadMath.divide("anything") will provide the somewhat-unhelpful error (FunctionClauseError) no function clause matching in BadMath.divide/1 — whereas if you had tried to run "anything" / 0 directly, you would get a more helpful error: (ArithmeticError) bad argument in arithmetic expression. Read basic use of guard clauses online: https://riptutorial.com/elixir/topic/6121/basic-use-of-guard- clauses https://riptutorial.com/ 9 Chapter 5: BEAM Examples Introduction iex> :observer.start :ok :observer.start opens the GUI observer interface, showing you CPU breakdown, memory usage, and other information critical to understanding the usage patterns of your applications. Read BEAM online: https://riptutorial.com/elixir/topic/3587/beam https://riptutorial.com/ 10 Chapter 6: Behaviours Examples Introduction Behaviours are a list of functions specifications that another module can implement. They are similar to interfaces in other languages. Here’s an example behaviour: defmodule Parser do @callback parse(String.t) :: any @callback extensions() :: [String.t] end And a module that implements it: defmodule JSONParser do @behaviour Parser def parse(str), do: # ... parse JSON def extensions, do: ["json"] end The @behaviour module attribute above indicates that this module is expected to define every function defined in the Parser module. Missing functions will result in undefined behaviour function compilation errors. Modules can have multiple @behaviour attributes. Read Behaviours online: https://riptutorial.com/elixir/topic/3558/behaviours https://riptutorial.com/ 11 Chapter 7: Better debugging with IO.inspect and labels Introduction IO.inspect is very useful when you try to debug your chains of method calling. It can get messy though if you use it too often. Since Elixir 1.4.0 the label option of IO.inspect can help Remarks Only works with Elixir 1.4+, but I can't tag that yet. Examples Without labels url |> IO.inspect |> HTTPoison.get! |> IO.inspect |> Map.get(:body) |> IO.inspect |> Poison.decode! |> IO.inspect This will result in a lot of output with no context: "https://jsonplaceholder.typicode.com/posts/1" %HTTPoison.Response{body: "{\n \"userId\": 1,\n \"id\": 1,\n \"title\": \"sunt aut facere repellat provident occaecati excepturi optio reprehenderit\",\n \"body\": \"quia et suscipit\\nsuscipit recusandae consequuntur expedita et cum\\nreprehenderit molestiae ut ut quas totam\\nnostrum rerum est autem sunt rem eveniet architecto\"\n}", headers: [{"Date", "Thu, 05 Jan 2017 14:29:59 GMT"}, {"Content-Type", "application/json; charset=utf-8"}, {"Content-Length", "292"}, {"Connection", "keep-alive"}, {"Set-Cookie", "__cfduid=d56d1be0a544fcbdbb262fee9477600c51483626599; expires=Fri, 05-Jan-18 14:29:59 GMT; path=/; domain=.typicode.com; HttpOnly"}, {"X-Powered-By", "Express"}, {"Vary", "Origin, Accept-Encoding"}, {"Access-Control-Allow-Credentials", "true"}, {"Cache-Control", "public, max-age=14400"}, {"Pragma", "no-cache"}, {"Expires", "Thu, 05 Jan 2017 18:29:59 GMT"}, {"X-Content-Type-Options", "nosniff"}, {"Etag", "W/\"124-yv65LoT2uMHrpn06wNpAcQ\""}, {"Via", "1.1 vegur"}, {"CF-Cache-Status", "HIT"}, {"Server", "cloudflare-nginx"}, {"CF-RAY", "31c7a025e94e2d41-TXL"}], status_code: 200} "{\n \"userId\": 1,\n \"id\": 1,\n \"title\": \"sunt aut facere repellat provident https://riptutorial.com/ 12 occaecati excepturi optio reprehenderit\",\n \"body\": \"quia et suscipit\\nsuscipit recusandae consequuntur expedita et cum\\nreprehenderit molestiae ut ut quas totam\\nnostrum rerum est autem sunt rem eveniet architecto\"\n}" %{"body" => "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto", "id" => 1, "title" => "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", "userId" => 1} With labels using the label option to add context can help a lot: url |> IO.inspect(label: "url") |> HTTPoison.get! |> IO.inspect(label: "raw http resonse") |> Map.get(:body) |> IO.inspect(label: "raw body") |> Poison.decode! |> IO.inspect(label: "parsed body") url: "https://jsonplaceholder.typicode.com/posts/1" raw http resonse: %HTTPoison.Response{body: "{\n \"userId\": 1,\n \"id\": 1,\n \"title\": \"sunt aut facere repellat provident occaecati excepturi optio reprehenderit\",\n \"body\": \"quia et suscipit\\nsuscipit recusandae consequuntur expedita et cum\\nreprehenderit molestiae ut ut quas totam\\nnostrum rerum est autem sunt rem eveniet architecto\"\n}", headers: [{"Date", "Thu, 05 Jan 2017 14:33:06 GMT"}, {"Content-Type", "application/json; charset=utf-8"}, {"Content-Length", "292"}, {"Connection", "keep-alive"}, {"Set-Cookie", "__cfduid=d22d817e48828169296605d27270af7e81483626786; expires=Fri, 05-Jan-18 14:33:06 GMT; path=/; domain=.typicode.com; HttpOnly"}, {"X-Powered-By", "Express"}, {"Vary", "Origin, Accept-Encoding"}, {"Access-Control-Allow-Credentials", "true"}, {"Cache-Control", "public, max-age=14400"}, {"Pragma", "no-cache"}, {"Expires", "Thu, 05 Jan 2017 18:33:06 GMT"}, {"X-Content-Type-Options", "nosniff"}, {"Etag", "W/\"124-yv65LoT2uMHrpn06wNpAcQ\""}, {"Via", "1.1 vegur"}, {"CF-Cache-Status", "HIT"}, {"Server", "cloudflare-nginx"}, {"CF-RAY", "31c7a4b8ae042d77-TXL"}], status_code: 200} raw body: "{\n \"userId\": 1,\n \"id\": 1,\n \"title\": \"sunt aut facere repellat provident occaecati excepturi optio reprehenderit\",\n \"body\": \"quia et suscipit\\nsuscipit recusandae consequuntur expedita et cum\\nreprehenderit molestiae ut ut quas totam\\nnostrum rerum est autem sunt rem eveniet architecto\"\n}" parsed body: %{"body" => "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto", "id" => 1, "title" => "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", "userId" => 1} Read Better debugging with IO.inspect and labels online: https://riptutorial.com/elixir/topic/8725/better-debugging-with-io-inspect-and-labels https://riptutorial.com/ 13 Chapter 8: Built-in types Examples Numbers Elixir comes with integers and floating point numbers. An integer literal can be written in decimal, binary, octal and hexadecimal formats. iex> x = 291 291 iex> x = 0b100100011 291 iex> x = 0o443 291 iex> x = 0x123 291 As Elixir uses bignum arithmetic, the range of integer is only limited by the available memory on the system. Floating point numbers are double precision and follows IEEE-754 specification. iex> x = 6.8 6.8 iex> x = 1.23e-11 1.23e-11 Note that Elixir also supports exponent form for floats. iex> 1 + 1 2 iex> 1.0 + 1.0 2.0 First we added two integers numbers, and the result is an integer. Later we added two floating point numbers, and the result is a floating point number. Dividing in Elixir always returns a floating point number: iex> 10 / 2 5.0 In the same way, if you add, subtract or multiply an integer by a floating point number the result will be floating point: https://riptutorial.com/ 14 iex> 40.0 + 2 42.0 iex> 10 - 5.0 5.0 iex> 3 * 3.0 9.0 For integer division, one can use the div/2 function: iex> div(10, 2) 5 Atoms Atoms are constants that represent a name of some thing. The value of an atom is it's name. An atom name starts with a colon. :atom # that's how we define an atom An atom's name is unique. Two atoms with the same names always are equal. iex(1)> a = :atom :atom iex(2)> b = :atom :atom iex(3)> a == b true iex(4)> a === b true Booleans true and false, actually are atoms. iex(1)> true == :true true iex(2)> true === :true true Atoms are stored in special atoms table. It's very important to know that this table is not garbage- collected. So, if you want (or accidentally it is a fact) constantly create atoms - it is a bad idea. Binaries and Bitstrings Binaries in elixir are created using the Kernel.SpecialForms construct <<>>. They are a powerful tool which makes Elixir very useful for working with binary protocols and encodings. https://riptutorial.com/ 15 Binaries and bitstrings are specified using a comma delimited list of integers or variable values, bookended by "<<" and ">>". They are composed of 'units', either a grouping of bits or a grouping of bytes. The default grouping is a single byte (8 bits), specified using an integer: <<222,173,190, 239>> # 0xDEADBEEF Elixir strings also convert directly to binaries: iex> <<0, "foo">> <<0, 102, 111, 111>> You can add "specifiers" to each "segment" of a binary, allowing you to encode: • • • Data Type Size Endianness These specifiers are encoded by following each value or variable with the "::" operator: <<102::integer-native>> <<102::native-integer>> # Same as above <<102::unsigned-big-integer>> <<102::unsigned-big-integer-size(8)>> <<102::unsigned-big-integer-8>> # Same as above <<102::8-integer-big-unsigned>> <<-102::signed-little-float-64>> # -102 as a little-endian Float64 <<-102::native-little-float-64>> # -102 as a Float64 for the current machine The available data types you can use are: • • • • • • • • • integer float bits (alias for bitstring) bitstring binary bytes (alias for binary) utf8 utf16 utf32 Be aware that when specifying the 'size' of the binary segment, it varies according to the 'type' chosen in the segment specifier: • • • integer (default) 1 bit float 1 bit binary 8 bits Read Built-in types online: https://riptutorial.com/elixir/topic/1774/built-in-types https://riptutorial.com/ 16 Chapter 9: Conditionals Remarks Note that the do...end syntax is syntactic sugar for regular keyword lists, so you can actually do this: unless false, do: IO.puts("Condition is false") # Outputs "Condition is false" # With an `else`: if false, do: IO.puts("Condition is true"), else: IO.puts("Condition is false") # Outputs "Condition is false" Examples case case {1, 2} do {3, 4} -> "This clause won't match." {1, x} -> "This clause will match and bind x to 2 in this clause." _ -> "This clause would match any value." end case is only used to match the given pattern of the particular data. Here , {1,2} is matching with different case pattern that is given in the code example. if and unless if true do "Will be seen since condition is true." end if false do "Won't be seen since condition is false." else "Will be seen. end unless false do "Will be seen." end unless true do "Won't be seen." else "Will be seen." end https://riptutorial.com/ 17 cond cond do 0 == 1 -> IO.puts "0 = 1" 2 == 1 + 1 -> IO.puts "1 + 1 = 2" 3 == 1 + 2 -> IO.puts "1 + 2 = 3" end # Outputs "1 + 1 = 2" (first condition evaluating to true) cond will raise a CondClauseError if no conditions are true. cond do 1 == 2 -> "Hmmm" "foo" == "bar" -> "What?" end # Error This can be avoided by adding a condition that will always be true. cond do ... other conditions true -> "Default value" end Unless it is never expected to reach the default case, and the program should in fact crash at that point. with clause with clause is used to combine matching clauses. It looks like we combine anonymous functions or handle function with multiple bodies (matching clauses). Consider the case: we create a user, insert it into DB, then create greet email and then send it to the user. Without the with clause we might write something like this (I omitted functions implementations): case create_user(user_params) do {:ok, user} -> case Mailer.compose_email(user) do {:ok, email} -> Mailer.send_email(email) {:error, reason} -> handle_error end {:error, changeset} -> handle_error end Here we handle our business process's flow with case (it could be cond or if). That leads us to so- called 'pyramid of doom', because we have to deal with possible conditions and decide: whether move further or not. It would be much nicer to rewrite this code with with statement: https://riptutorial.com/ 18 with {:ok, user} <- create_user(user_params), {:ok, email} <- Mailer.compose_email(user) do {:ok, Mailer.send_email} else {:error, _reason} -> handle_error end In the code snippet above we've rewrite nested case clauses with with. Within with we invoke some functions (either anonymous or named) and pattern match on their outputs. If all matched, with return do block result, or else block result otherwise. We can omit else so with will return either do block result or the first fail result. So, the value of with statement is its do block result. Read Conditionals online: https://riptutorial.com/elixir/topic/2118/conditionals https://riptutorial.com/ 19 Chapter 10: Constants Remarks So this is a summary analysis I've done based on the methods listed at How do you define constants in Elixir modules?. I'm posting it for a couple reasons: • • • Most Elixir documentation is quite thorough, but I found this key architectural decision lacking guidance - so I would have requested it as a topic. I wanted to get a little visibility and comments from others about the topic. I also wanted to test out the new SO Documentation workflow. ;) I've also uploaded the entire code to the GitHub repo elixir-constants-concept. Examples Module-scoped constants defmodule MyModule do @my_favorite_number 13 @use_snake_case "This is a string (use double-quotes)" end These are only accessible from within this module. Constants as functions Declare: defmodule MyApp.ViaFunctions.Constants do def app_version, do: "0.0.1" def app_author, do: "Felix Orr" def app_info, do: [app_version, app_author] def bar, do: "barrific constant in function" end Consume with require: defmodule MyApp.ViaFunctions.ConsumeWithRequire do require MyApp.ViaFunctions.Constants def foo() do IO.puts MyApp.ViaFunctions.Constants.app_version IO.puts MyApp.ViaFunctions.Constants.app_author IO.puts inspect MyApp.ViaFunctions.Constants.app_info end # This generates a compiler error, cannot invoke `bar/0` inside a guard. # def foo(_bar) when is_bitstring(bar) do https://riptutorial.com/ 20 # IO.puts "We just used bar in a guard: #{bar}" # end end Consume with import: defmodule MyApp.ViaFunctions.ConsumeWithImport do import MyApp.ViaFunctions.Constants def foo() do IO.puts app_version IO.puts app_author IO.puts inspect app_info end end This method allows for reuse of constants across projects, but they will not be usable within guard functions that require compile-time constants. Constants via macros Declare: defmodule MyApp.ViaMacros.Constants do @moduledoc """ Apply with `use MyApp.ViaMacros.Constants, :app` or `import MyApp.ViaMacros.Constants, :app`. Each constant is private to avoid ambiguity when importing multiple modules that each have their own copies of these constants. """ def app do quote do # This method allows sharing module constants which can be used in guards. @bar "barrific module constant" defp app_version, do: "0.0.1" defp app_author, do: "Felix Orr" defp app_info, do: [app_version, app_author] end end defmacro __using__(which) when is_atom(which) do apply(__MODULE__, which, []) end end Consume with use: defmodule MyApp.ViaMacros.ConsumeWithUse do use MyApp.ViaMacros.Constants, :app def foo() do IO.puts app_version IO.puts app_author IO.puts inspect app_info https://riptutorial.com/ 21 end def foo(_bar) when is_bitstring(@bar) do IO.puts "We just used bar in a guard: #{@bar}" end end This method allows you to use the @some_constant inside guards. I'm not even sure that the functions would be strictly necessary. Read Constants online: https://riptutorial.com/elixir/topic/6614/constants https://riptutorial.com/ 22 Chapter 11: Data Structures Syntax • • [head | tail] = [1, 2, 3, true] # one can use pattern matching to break up cons cells. This assigns head to 1 and tail to [2, 3, true] %{d: val} = %{d: 1, e: true} # this assigns val to 1; no variable d is created because the d on the lhs is really just a symbol that is used to create the pattern %{:d => _} (note that hash rocket notation allows one to have non-symbols as keys for maps just like in ruby) Remarks As for which data structure to us here are some brief remarks. If you need an array data structure if you're going to be doing a lot of writing use lists. If instead you are going to be doing a lot of read you should use tuples. As for maps they are just simply how you do key value stores. Examples Lists a = [1, 2, 3, true] Note that these are stored in memory as linked lists. Id est this is a series of cons cells where the head (List.hd/1) is the value of first item of the list and the tail (List.tail/1) is the value of the rest of the list. List.hd(a) = 1 List.tl(a) = [2, 3, true] Tuples b = {:ok, 1, 2} Tuples are the equivalent of arrays in other languages. They are stored contiguously in memory. Read Data Structures online: https://riptutorial.com/elixir/topic/1607/data-structures https://riptutorial.com/ 23 Chapter 12: Debugging Tips Examples Debugging with IEX.pry/0 Debugging with IEx.pry/0 is quite simple. 1. 2. 3. require IEx in your module Find the line of code you want to inspect Add IEx.pry after the line Now start your project (e.g. iex -S mix). When the line with IEx.pry/0 is reached the program will stop and you have the chance to inspect. It is like a breakpoint in a traditional debugger. When you are finished just type respawn into the console. require IEx; defmodule Example do def double_sum(x, y) do IEx.pry hard_work(x, y) end defp hard_work(x, y) do 2 * (x + y) end end Debugging with IO.inspect/1 It is possible to use IO.inspect/1 as a tool to debug an elixir program. defmodule MyModule do def myfunction(argument_1, argument_2) do IO.inspect(argument_1) IO.inspect(argument_2) end end It will print out argument_1 and argument_2 to the console. Since IO.inspect/1 returns its argument it is very easy to include it in function calls or pipelines without breaking the flow: do_something(a, b) |> do_something_else(c) # can be adorned with IO.inspect, with no change in functionality: https://riptutorial.com/ 24 do_something(IO.inspect(a), IO.inspect(b)) |> IO.inspect do_something(IO.inspect(c)) Debug in pipe defmodule Demo do def foo do 1..10 |> Enum.map(&(&1 * &1)) |> p |> Enum.filter(&rem(&1, 2) == 0) |> p |> Enum.take(3) |> p end defp p(e) do require Logger Logger.debug inspect e, limit: :infinity e end end iex(1)> Demo.foo 23:23:55.171 [debug] [1, 4, 9, 16, 25, 36, 49, 64, 81, 100] 23:23:55.171 [debug] [4, 16, 36, 64, 100] 23:23:55.171 [debug] [4, 16, 36] [4, 16, 36] Pry in pipe defmodule Demo do def foo do 1..10 |> Enum.map(&(&1 * &1)) |> Enum.filter(&rem(&1, 2) == 0) |> pry |> Enum.take(3) end defp pry(e) do require IEx IEx.pry e end end iex(1)> Demo.foo Request to pry #PID<0.117.0> at lib/demo.ex:11 def pry(e) do require IEx https://riptutorial.com/ 25 IEx.pry e end Allow? [Yn] Y Interactive Elixir (1.3.2) - press Ctrl+C to exit (type h() ENTER for help) pry(1)> e [4, 16, 36, 64, 100] pry(2)> respawn Interactive Elixir (1.3.2) - press Ctrl+C to exit (type h() ENTER for help) [4, 16, 36] iex(1)> Read Debugging Tips online: https://riptutorial.com/elixir/topic/2719/debugging-tips https://riptutorial.com/ 26 Chapter 13: Doctests Examples Introduction When you document your code with @doc, you can supply code examples like so: # myproject/lib/my_module.exs defmodule MyModule do @doc """ Given a number, returns `true` if the number is even, otherwise `false`. ## Example iex> MyModule.even?(2) true iex> MyModule.even?(3) false """ def even?(number) do rem(number, 2) == 0 end end You can add the code examples as test cases into one of your test suites: # myproject/test/doc_test.exs defmodule DocTest do use ExUnit.Case doctest MyModule end Then, you can then run your tests with mix test. Generating HTML documentation based on doctest Because generating documentation is based on markdown, you have to do 2 things : 1/ Write your doctest and make your doctest examples clear to improve readability (It is better to give a headline, like "examples" or "tests"). When you write your tests, do not forget to give 4 spaces to your tests code so that it will be formatting as code in the HTML documentation. 2/ Then, enter "mix docs" in console at the root of your elixir project to generate the HTML documentation in the doc directory located in the root of your elixir project. $> mix docs Multiline doctests https://riptutorial.com/ 27 You can do a multiline doctest by using '...>' for the lines following the first iex> Foo.Bar.somethingConditional("baz") ...> |> case do ...> {:ok, _} -> true ...> {:error, _} -> false ...> end true Read Doctests online: https://riptutorial.com/elixir/topic/2708/doctests https://riptutorial.com/ 28 Chapter 14: Ecto Examples Adding a Ecto.Repo in an elixir program This can be done in 3 steps : 1. You must define an elixir module which use Ecto.Repo and register your app as an otp_app. defmodule Repo do use Ecto.Repo, otp_app: :custom_app end 2. You must also define some config for the Repo which will allow you to connect to the database. Here is an example with postgres. config :custom_app, Repo, adapter: Ecto.Adapters.Postgres, database: "ecto_custom_dev", username: "postgres_dev", password: "postgres_dev", hostname: "localhost", # OR use a URL to connect instead url: "postgres://postgres_dev:postgres_dev@localhost/ecto_custom_dev" 3. Before using Ecto in your application, you need to ensure that Ecto is started before your app is started. It can be done with registering Ecto in lib/custom_app.ex as a supervisor. def start(_type, _args) do import Supervisor.Spec children = [ supervisor(Repo, []) ] opts = [strategy: :one_for_one, name: MyApp.Supervisor] Supervisor.start_link(children, opts) end "and" clause in a Repo.get_by/3 If you have an Ecto.Queryable, named Post, which has a title and an description. You can fetch the Post with title: "hello" and description : "world" by performing : MyRepo.get_by(Post, [title: "hello", description: "world"]) All of this is possible because Repo.get_by expects in second argument a Keyword List. https://riptutorial.com/ 29 Querying with dynamic fields To query a field which name is contained in a variable, use the field function. some_field = :id some_value = 10 from p in Post, where: field(p, ^some_field) == ^some_value Add custom data types to migration and to schema (From this answer) The example below adds an enumerated type to a postgres database. First, edit the migration file (created with mix ecto.gen.migration): def up do # creating the enumerated type execute("CREATE TYPE post_status AS ENUM ('published', 'editing')") # creating a table with the column create table(:posts) do add :post_status, :post_status, null: false end end def down do drop table(:posts) execute("DROP TYPE post_status") end Second, in the model file either add a field with an Elixir type : schema "posts" do field :post_status, :string end or implement the Ecto.Type behaviour. A good example for the latter is the ecto_enum package and it can be used as a template. Its usage is well documented on its github page. This commit shows an example usage in a Phoenix project from adding enum_ecto to the project and using the enumerated type in views and models. Read Ecto online: https://riptutorial.com/elixir/topic/6524/ecto https://riptutorial.com/ 30 Chapter 15: Erlang Examples Using Erlang Erlang modules are available as atoms. For example, the Erlang math module is available as :math: iex> :math.pi 3.141592653589793 Inspect an Erlang module Use module_info on Erlang modules you wish to inspect: iex> :math.module_info [module: :math, exports: [pi: 0, module_info: 0, module_info: 1, pow: 2, atan2: 2, sqrt: 1, log10: 1, log2: 1, log: 1, exp: 1, erfc: 1, erf: 1, atanh: 1, atan: 1, asinh: 1, asin: 1, acosh: 1, acos: 1, tanh: 1, tan: 1, sinh: 1, sin: 1, cosh: 1, cos: 1], attributes: [vsn: [113168357788724588783826225069997113388]], compile: [options: [{:outdir, '/private/tmp/erlang20160316-36404-xtp7cq/otp-OTP-18.3/lib/stdlib/src/../ebin'}, {:i, '/private/tmp/erlang20160316-36404-xtp7cq/otp-OTP-18.3/lib/stdlib/src/../include'}, {:i, '/private/tmp/erlang20160316-36404-xtp7cq/otp-OTP- 18.3/lib/stdlib/src/../../kernel/include'}, :warnings_as_errors, :debug_info], version: '6.0.2', time: {2016, 3, 16, 16, 40, 35}, source: '/private/tmp/erlang20160316-36404-xtp7cq/otp-OTP-18.3/lib/stdlib/src/math.erl'], native: false, md5: <<85, 35, 110, 210, 174, 113, 103, 228, 63, 252, 81, 27, 224, 15, 64, 44>>] Read Erlang online: https://riptutorial.com/elixir/topic/2716/erlang https://riptutorial.com/ 31 Chapter 16: ExDoc Examples Introduction To generate documentation in HTML format from @doc and @moduledoc attributes in your source code, add ex_doc and a markdown processor, right now ExDoc supports Earmark, Pandoc, Hoedown and Cmark, as dependencies into your mix.exs file: # config/mix.exs def deps do [{:ex_doc, "~> 0.11", only: :dev}, {:earmark, "~> 0.1", only: :dev}] end If you want to use another Markdown processor, you can find more information in the Changing the Markdown tool section. You can use Markdown within Elixir @doc and @moduledoc attributes. Then, run mix docs. One thing to keep in mind is that ExDoc allows configuration parameters, such as: def project do [app: :my_app, version: "0.1.0-dev", name: "My App", source_url: "https://github.com/USER/APP", homepage_url: "http://YOUR_PROJECT_HOMEPAGE", deps: deps(), docs: [logo: "path/to/logo.png", output: "docs", main: "README", extra_section: "GUIDES", extras: ["README.md", "CONTRIBUTING.md"]]] end You can see more information about this configuration options with mix help docs Read ExDoc online: https://riptutorial.com/elixir/topic/3582/exdoc https://riptutorial.com/ 32 Chapter 17: ExUnit Examples Asserting Exceptions Use assert_raise to test if an exception was raised. assert_raise takes in an Exception and a function to be executed. test "invalid block size" do assert_raise(MerkleTree.ArgumentError, (fn() -> MerkleTree.new ["a", "b", "c"] end)) end Wrap any code you want to test in an anonymous function and pass it to assert_raise. Read ExUnit online: https://riptutorial.com/elixir/topic/3583/exunit https://riptutorial.com/ 33 Chapter 18: Functional programming in Elixir Introduction Let's try to implement the basic higher orders functions like map and reduce using Elixir Examples Map Map is a function which will take an array and a function and return an array after applying that function to each element in that list defmodule MyList do def map([], _func) do [] end def map([head | tail], func) do [func.(head) | map(tail, func)] end end Copy paste in iex and execute: MyList.map [1,2,3], fn a -> a * 5 end Shorthand syntax is MyList.map [1,2,3], &(&1 * 5) Reduce Reduce is a function which will take an array, function and accumulator and use accumulator as seed to start the iteration with the first element to give next accumulator and the iteration continues for all the elements in the array (refer below example) defmodule MyList do def reduce([], _func, acc) do acc end def reduce([head | tail], func, acc) do reduce(tail, func, func.(acc, head)) end end Copy paste the above snippet in iex: 1. To add all numbers in an array: MyList.reduce [1,2,3,4], fn acc, element -> acc + element end, 0 https://riptutorial.com/ 34 2. To mutliply all numbers in an array: MyList.reduce [1,2,3,4], fn acc, element -> acc * element end, 1 Explanation for example 1: Iteration 1 => acc = 0, element = 1 ==> 0 + 1 ===> 1 = next accumulator Iteration 2 => acc = 1, element = 2 ==> 1 + 2 ===> 3 = next accumulator Iteration 3 => acc = 3, element = 3 ==> 3 + 3 ===> 6 = next accumulator Iteration 4 => acc = 6, element = 4 ==> 6 + 4 ===> 10 = next accumulator = result(as all elements are done) Filter the list using reduce MyList.reduce [1,2,3,4], fn acc, element -> if rem(element,2) == 0 do acc else acc ++ [element] end end, [] Read Functional programming in Elixir online: https://riptutorial.com/elixir/topic/10186/functional- programming-in-elixir https://riptutorial.com/ 35 Chapter 19: Functions Examples Anonymous Functions In Elixir, a common practice is to use anonymous functions. Creating an anonymous function is simple: iex(1)> my_func = fn x -> x * 2 end #Function<6.52032458/1 in :erl_eval.expr/5> The general syntax is: fn args -> output end For readability, you may put parenthesis around the arguments: iex(2)> my_func = fn (x, y) -> x*y end #Function<12.52032458/2 in :erl_eval.expr/5> To invoke an anonymous function, call it by the assigned name and add . between the name and arguments. iex(3)>my_func.(7, 5) 35 It is possible to declare anonymous functions without arguments: iex(4)> my_func2 = fn -> IO.puts "hello there" end iex(5)> my_func2.() hello there :ok Using the capture operator To make anonymous functions more concise you can use the capture operator &. For example, instead of: iex(5)> my_func = fn (x) -> x*x*x end You can write: iex(6)> my_func = &(&1*&1*&1) https://riptutorial.com/ 36 With multiple parameters, use the number corresponding to each argument, counting from 1: iex(7)> my_func = fn (x, y) -> x + y end iex(8)> my_func = &(&1 + &2) # &1 stands for x and &2 stands for y iex(9)> my_func.(4, 5) 9 Multiple bodies An anonymous function can also have multiple bodies (as a result of pattern matching): my_func = fn param1 -> do_this param2 -> do_that end When you call a function with multiple bodies Elixir attempts to match the parameters you have provided with the proper function body. Keyword lists as function parameters Use keyword lists for 'options'-style parameters that contains multiple key-value pairs: def myfunc(arg1, opts \\ []) do # Function body end We can call the function above like so: iex> myfunc "hello", pizza: true, soda: false which is equivalent to: iex> myfunc("hello", [pizza: true, soda: false]) The argument values are available as opts.pizza and opts.soda respectively. Alternatively, you could use atoms: opts[:pizza] and opts[:soda]. Named Functions & Private Functions Named Functions defmodule Math do # one way def add(a, b) do a + b https://riptutorial.com/ 37 end # another way def subtract(a, b), do: a - b end iex> Math.add(2, 3) 5 :ok iex> Math.subtract(5, 2) 3 :ok Private Functions defmodule Math do def sum(a, b) do add(a, b) end # Private Function defp add(a, b) do a + b end end iex> Math.add(2, 3) ** (UndefinedFunctionError) undefined function Math.add/2 Math.add(3, 4) iex> Math.sum(2, 3) 5 Pattern Matching Elixir matches a function call to its body based on the value of its arguments. defmodule Math do def factorial(0): do: 1 def factorial(n): do: n * factorial(n - 1) end Here, factorial of positive numbers matches the second clause, while factorial(0) matches the first. (ignoring negative numbers for the sake of simplicity). Elixir tries to match the functions from top to bottom. If the second function is written above the first, we will an unexpected result as it goes to an endless recursion. Because factorial(0) matches to factorial(n) Guard clauses Guard clauses enables us to check the arguments before executing the function. Guard clauses are usually preferred to if and cond due to their readability, and to make a certain optimization technique easier for the compiler. The first function definition where all guards match is executed. Here is an example implementation of the factorial function using guards and pattern matching. https://riptutorial.com/ 38 defmodule Math do def factorial(0), do: 1 def factorial(n) when n > 0: do: n * factorial(n - 1) end The first pattern matches if (and only if) the argument is 0. If the argument is not 0, the pattern match fails and the next function below is checked. That second function definition has a guard clause: when n > 0. This means that this function only matches if the argument n is greater than 0. After all, the mathematical factorial function is not defined for negative integers. If neither function definition (including their pattern matching and guard clauses) match, a FunctionClauseError will be raised. This happens for this function when we pass a negative number as the argument, since it is not defined for negative numbers. Note that this FunctionClauseError itself, is not a mistake. Returning -1 or 0 or some other "error value" as is common in some other languages would hide the fact that you called an undefined function, hiding the source of the error, possibly creating a huge painful bug for a future developer. Default Parameters You can pass default parameters to any named function using the syntax: param \\ value: defmodule Example do def func(p1, p2 \\ 2) do IO.inspect [p1, p2] end end Example.func("a") # => ["a", 2] Example.func("b", 4) # => ["b", 4] Capture functions Use & to capture functions from other modules. You can use the captured functions directly as function parameters or within anonymous functions. Enum.map(list, fn(x) -> String.capitalize(x) end) Can be made more concise using &: Enum.map(list, &String.capitalize(&1)) Capturing functions without passing any arguments require you to explicitly specify its arity, e.g. &String.capitalize/1: defmodule Bob do def say(message, f \\ &String.capitalize/1) do f.(message) https://riptutorial.com/ 39 end end Read Functions online: https://riptutorial.com/elixir/topic/2442/functions https://riptutorial.com/ 40 Chapter 20: Getting help in IEx console Introduction IEx provides access to Elixir documentation. When Elixir is installed on your system you can start IEx e.g. with iex command in a terminal. Then type h command on IEx command line followed by the function name prepended by its module name e.g. h List.foldr Examples Listing Elixir modules and functions To get the list of Elixir modules just type h Elixir.[TAB] Pressing [TAB] autocompletes modules and functions names. In this case it lists all modules. To find all functions in a module e.g. List use h List.[TAB] Read Getting help in IEx console online: https://riptutorial.com/elixir/topic/10780/getting-help-in- iex-console https://riptutorial.com/ 41 Chapter 21: IEx Console Tips & Tricks Examples Recompile project with `recompile` iex(1)> recompile Compiling 1 file (.ex) :ok See documentation with `h` iex(1)> h List.last def last(list) Returns the last element in list or nil if list is empty. Examples ┃ iex> List.last([]) ┃ nil ┃ ┃ iex> List.last([1]) ┃ 1 ┃ ┃ iex> List.last([1, 2, 3]) ┃ 3 Get value from last command with `v` iex(1)> 1 + 1 2 iex(2)> v 2 iex(3)> 1 + v 3 See also: Get the value of a row with `v` Get the value of a previous command with `v` iex(1)> a = 10 10 iex(2)> b = 20 20 iex(3)> a + b 30 You can get a specific row passing the index of the row: https://riptutorial.com/ 42 iex(4)> v(3) 30 You can also specify an index relative to the current row: iex(5)> v(-1) # Retrieves value of row (5-1) -> 4 30 iex(6)> v(-5) # Retrieves value of row (5-4) -> 1 10 The value can be reused in other calculations: iex(7)> v(2) * 4 80 If you specify a non-existing row, IEx will raise an error: iex(7)> v(100) ** (RuntimeError) v(100) is out of bounds (iex) lib/iex/history.ex:121: IEx.History.nth/2 (iex) lib/iex/helpers.ex:357: IEx.Helpers.v/1 Exit IEx console 1. Use Ctrl + C, Ctrl + C to exit iex(1)> BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded (v)ersion (k)ill (D)b-tables (d)istribution 2. Use Ctrl+ \ to immediately exit See information with `i` iex(1)> i :ok Term :ok Data type Atom Reference modules Atom iex(2)> x = "mystring" "mystring" iex(3)> i x Term "mystring" Data type BitString Byte size 8 Description This is a string: a UTF-8 encoded binary. It's printed surrounded by "double quotes" because all UTF-8 encoded codepoints in it are printable. https://riptutorial.com/ 43 Raw representation <<109, 121, 115, 116, 114, 105, 110, 103>> Reference modules String, :binary Creating PID This is useful when you didn't store the PID from a previous command iex(1)> self() #PID<0.138.0> iex(2)> pid("0.138.0") #PID<0.138.0> iex(3)> pid(0, 138, 0) #PID<0.138.0> Have your aliases ready when you start IEx If you put your commonly used aliases into an .iex.exs file at the root of your app, IEx will load them for you on startup. alias App.{User, Repo} Persistent history By default, user input history in IEx do not persist across different sessions. erlang-history adds history support to both the Erlang shell and IEx: git clone git@github.com:ferd/erlang-history.git cd erlang-history sudo make install You can now access your previous inputs using the up and down arrow keys, even across different IEx sessions. When Elixir console is stuck... Sometimes you might accidentally run something in the shell that ends up waiting forever, and thus blocking the shell: iex(2)> receive do _ -> :stuck end In that case, press Ctrl-g. You'll see: User switch command Enter these commands in order: • k (to kill the shell process) https://riptutorial.com/ 44 • • s (to start a new shell process) c (to connect to the new shell process) You'll end up in a new Erlang shell: Eshell V8.0.2 (abort with ^G) 1> To start an Elixir shell, type: 'Elixir.IEx.CLI':local_start(). (don't forget the final dot!) Then you'll see a new Elixir shell process coming up: Interactive Elixir (1.3.2) - press Ctrl+C to exit (type h() ENTER for help) iex(1)> "I'm back" "I'm back" iex(2)> To escape from “awaiting-for-more-input” mode (due to unclosed quotation mark, bracket etc,) type #iex:break, followed by carriage return ((cid:0)): iex(1)> "Hello, "world" ...(1)> ...(1)> #iex:break ** (TokenMissingError) iex:1: incomplete expression iex(1)> the above is specifically useful when copy-pasting a relatively huge snippet turns the console to “awaiting-for-more-input” mode. break out of incomplete expression When you have entered something into IEx which expects a completion, such as a multiline string, IEx will change the prompt to indicate that it is waiting for you finish by changing the prompt to have an ellipsis (...) rather than iex. If you find that IEx is waiting for you to finish an expression but you aren't sure what it needs to terminate the expression, or you simply want to abort this line of input, enter #iex:break as the console input. This will cause IEx to throw a TokenMissingError and cancel waiting for any more input, returning you to a standard "top-level" console input. iex:1> "foo" "foo" iex:2> "bar ...:2> #iex:break ** (TokenMissingError) iex:2: incomplete expression https://riptutorial.com/ 45 More info is available at the IEx documentation. Load a module or script into the IEx session If you have an elixir file; a script or a module and want to load it into the current IEx session, you can use the c/1 method: iex(1)> c "lib/utils.ex" iex(2)> Utils.some_method This will compile and load the module in IEx, and you'll be able to call all of it's public methods. For scripts, it will immediately execute the contents of the script: iex(3)> c "/path/to/my/script.exs" Called from within the script! Read IEx Console Tips & Tricks online: https://riptutorial.com/elixir/topic/1283/iex-console-tips--- tricks https://riptutorial.com/ 46 Chapter 22: Installation Examples Fedora Installation dnf install erlang elixir OSX Installation On OS X and MacOS, Elixir can be installed via the common package managers: Homebrew $ brew update $ brew install elixir Macports $ sudo port install elixir Debian/Ubuntu Installation # Fetch and install package to setup access to the official APT repository wget https://packages.erlang-solutions.com/erlang-solutions_1.0_all.deb sudo dpkg -i erlang-solutions_1.0_all.deb # Update package index sudo apt-get update # Install Erlang and Elixir sudo apt-get install esl-erlang sudo apt-get install elixir Gentoo/Funtoo Installation Elixir is available in main packages repository. Update the packages list before installing any package: emerge --sync This is one step installation: https://riptutorial.com/ 47 emerge --ask dev-lang/elixir Read Installation online: https://riptutorial.com/elixir/topic/4208/installation https://riptutorial.com/ 48 Chapter 23: Join Strings Examples Using String Interpolation iex(1)> [x, y] = ["String1", "String2"] iex(2)> "#{x} #{y}" # "String1 String2" Using IO List ["String1", " ", "String2"] |> IO.iodata_to_binary # "String1 String2" This will gives some performances boosts as strings not duplicated in memory. Alternative method: iex(1)> IO.puts(["String1", " ", "String2"]) # String1 String2 Using Enum.join Enum.join(["String1", "String2"], " ") # "String1 String2" Read Join Strings online: https://riptutorial.com/elixir/topic/9202/join-strings https://riptutorial.com/ 49 Chapter 24: Lists Syntax • • • • • • • • • • • [] [1, 2, 3, 4] [1, 2] ++ [3, 4] # -> [1,2,3,4] hd([1, 2, 3, 4]) # -> 1 tl([1, 2, 3, 4]) # -> [2,3,4] [head | tail] [1 | [2, 3, 4]] # -> [1,2,3,4] [1 | [2 | [3 | [4 | []]]]] -> [1,2,3,4] 'hello' = [?h, ?e, ?l, ?l, ?o] keyword_list = [a: 123, b: 456, c: 789] keyword_list[:a] # -> 123 Examples Keyword Lists Keyword lists are lists where each item in the list is a tuple of an atom followed by a value. keyword_list = [{:a, 123}, {:b, 456}, {:c, 789}] A shorthand notation for writing keyword lists is as follows: keyword_list = [a: 123, b: 456, c: 789] Keyword lists are useful for creating ordered key-value pair data structures, where multiple items can exist for a given key. The first item in a keyword list for a given key can be obtained like so: iex> keyword_list[:b] 456 A use case for keyword lists could be a sequence of named tasks to run: defmodule TaskRunner do def run_tasks(tasks) do # Call a function for each item in the keyword list. # Use pattern matching on each {:key, value} tuple in the keyword list Enum.each(tasks, fn {:delete, x} -> IO.puts("Deleting record " <> to_string(x) <> "...") {:add, value} -> https://riptutorial.com/ 50 IO.puts("Adding record \"" <> value <> "\"...") {:update, {x, value}} -> IO.puts("Setting record " <> to_string(x) <> " to \"" <> value <> "\"...") end) end end This code can be called with a keyword list like so: iex> tasks = [ ...> add: "foo", ...> add: "bar", ...> add: "test", ...> delete: 2, ...> update: {1, "asdf"} ...> ] iex> TaskRunner.run_tasks(tasks) Adding record "foo"... Adding record "bar"... Adding record "test"... Deleting record 2... Setting record 1 to "asdf"... Char Lists Strings in Elixir are "binaries". However, in Erlang code, strings are traditionally "char lists", so when calling Erlang functions, you may have to use char lists instead of regular Elixir strings. While regular strings are written using double quotes ", char lists are written using single quotes ': string = "Hello!" char_list = 'Hello!' Char lists are simply lists of integers representing the code points of each character. 'hello' = [104, 101, 108, 108, 111] A string can be converted to a char list with to_charlist/1: iex> to_charlist("hello") 'hello' And the reverse can be done with to_string/1: iex> to_string('hello') "hello" Calling an Erlang function and converting the output to a regular Elixir string: iex> :os.getenv |> hd |> to_string "PATH=/usr/local/bin:/usr/bin:/bin" https://riptutorial.com/ 51 Cons Cells Lists in Elixir are linked lists. This means that each item in a list consists of a value, followed by a pointer to the next item in the list. This is implemented in Elixir using cons cells. Cons cells are simple data structures with a "left" and a "right" value, or a "head" and a "tail". A | symbol can be added before the last item in a list to notate an (improper) list with a given head and tail. The following is a single cons cell with 1 as the head and 2 as the tail: [1 | 2] The standard Elixir syntax for a list is actually equivalent to writing a chain of nested cons cells: [1, 2, 3, 4] = [1 | [2 | [3 | [4 | []]]]] The empty list [] is used as the tail of a cons cell to represent the end of a list. All lists in Elixir are equivalent to the form [head | tail], where head is the first item of the list and tail is the rest of the list, minus the head. iex> [head | tail] = [1, 2, 3, 4] [1, 2, 3, 4] iex> head 1 iex> tail [2, 3, 4] Using the [head | tail] notation is useful for pattern matching in recursive functions: def sum([]), do: 0 def sum([head | tail]) do head + sum(tail) end Mapping Lists map is a function in functional programming which given a list and a function, returns a new list with the function applied to each item in that list. In Elixir, the map/2 function is in the Enum module. iex> Enum.map([1, 2, 3, 4], fn(x) -> x + 1 end) [2, 3, 4, 5] Using the alternative capture syntax for anonymous functions: iex> Enum.map([1, 2, 3, 4], &(&1 + 1)) [2, 3, 4, 5] https://riptutorial.com/ 52 Referring to a function with capture syntax: iex> Enum.map([1, 2, 3, 4], &to_string/1) ["1", "2", "3", "4"] Chaining list operations using the pipe operator: iex> [1, 2, 3, 4] ...> |> Enum.map(&to_string/1) ...> |> Enum.map(&("Chapter " <> &1)) ["Chapter 1", "Chapter 2", "Chapter 3", "Chapter 4"] List Comprehensions Elixir doesn't have loops. Instead of them for lists there are great Enum and List modules, but there are also List Comprehensions. List Comprehensions can be useful to: • create new lists iex(1)> for value <- [1, 2, 3], do: value + 1 [2, 3, 4] • filtering lists, using guard expressions but you use them without when keyword. iex(2)> odd? = fn x -> rem(x, 2) == 1 end iex(3)> for value <- [1, 2, 3], odd?.(value), do: value [1, 3] • create custom map, using into keyword: iex(4)> for value <- [1, 2, 3], into: %{}, do: {value, value + 1} %{1 => 2, 2=>3, 3 => 4} Combined example iex(5)> for value <- [1, 2, 3], odd?.(value), into: %{}, do: {value, value * value} %{1 => 1, 3 => 9} Summary List Comprehensions: • uses for..do syntax with additional guards after commas and into keyword when returning other structure than lists ie. map. https://riptutorial.com/ 53 • • • • in other cases return new lists doesn't support accumulators can't stop processing when certain condition is met guard statements have to be first in order after for and before do or into symbols. Order of symbols doesn't matter According to these constraints List Comprehensions are limited only for simple usage. In more advanced cases using functions from Enum and List modules would be the best idea. List difference iex> [1, 2, 3] -- [1, 3] [2] -- removes the first occurrence of an item on the left list for each item on the right. List Membership Use in operator to check if an element is a member of a list. iex> 2 in [1, 2, 3] true iex> "bob" in [1, 2, 3] false Converting Lists to a Map Use Enum.chunk/2 to group elements into sub-lists, and Map.new/2 to convert it into a Map: [1, 2, 3, 4, 5, 6] |> Enum.chunk(2) |> Map.new(fn [k, v] -> {k, v} end) Would give: %{1 => 2, 3 => 4, 5 => 6} Read Lists online: https://riptutorial.com/elixir/topic/1279/lists https://riptutorial.com/ 54 Chapter 25: Maps and Keyword Lists Syntax • • • • map = %{} // creates an empty map map = %{:a => 1, :b => 2} // creates a non-empty map list = [] // creates an empty list list = [{:a, 1}, {:b, 2}] // creates a non-empty keyword list Remarks Elixir provides two associative data structures: maps and keyword lists. Maps are the Elixir key-value (also called dictionary or hash in other languages) type. Keyword lists are tuples of key/value that associate a value to a certain key. They are generally used as options for a function call. Examples Creating a Map Maps are the Elixir key-value (also called dictionary or hash in other languages) type. You create a map using the %w{} syntax: %{} // creates an empty map %{:a => 1, :b => 2} // creates a non-empty map Keys and values can use be any type: %{"a" => 1, "b" => 2} %{1 => "a", 2 => "b"} Moreover, you can have maps with mixed types for both keys and values": // keys are integer or strings %{1 => "a", "b" => :foo} // values are string or nil %{1 => "a", 2 => nil} When all the keys in a map are atoms, you can use the keyword syntax for convenience: %{a: 1, b: 2} Creating a Keyword List https://riptutorial.com/ 55 Keyword lists are tuples of key/value, generally used as options for a function call. [{:a, 1}, {:b, 2}] // creates a non-empty keyword list Keyword lists can have the same key repeated more than once. [{:a, 1}, {:a, 2}, {:b, 2}] [{:a, 1}, {:b, 2}, {:a, 2}] Keys and values can be any type: [{"a", 1}, {:a, 2}, {2, "b"}] Difference between Maps and Keyword Lists Maps and keyword lists have different application. For instance, a map cannot have two keys with the same value and it's not ordered. Conversely, a Keyword list can be a little bit hard to use in pattern matching in some cases. Here's a few use cases for maps vs keyword lists. Use keyword lists when: • • you need the elements to be ordered you need more than one element with the same key Use maps when: • • • you want to pattern-match against some keys/values you don't need more than one element with the same key whenever you don't explicitly need a keyword list Read Maps and Keyword Lists online: https://riptutorial.com/elixir/topic/2706/maps-and-keyword- lists https://riptutorial.com/ 56 Chapter 26: Metaprogramming Examples Generate tests at compile time defmodule ATest do use ExUnit.Case [{1, 2, 3}, {10, 20, 40}, {100, 200, 300}] |> Enum.each(fn {a, b, c} -> test "#{a} + #{b} = #{c}" do assert unquote(a) + unquote(b) = unquote(c) end end) end Output: . 1) test 10 + 20 = 40 (Test.Test) test.exs:6 match (=) failed code: 10 + 20 = 40 rhs: 40 stacktrace: test.exs:7 . Finished in 0.1 seconds (0.1s on load, 0.00s on tests) 3 tests, 1 failure Read Metaprogramming online: https://riptutorial.com/elixir/topic/4069/metaprogramming https://riptutorial.com/ 57 Chapter 27: Mix Examples Create a Custom Mix Task # lib/mix/tasks/mytask.ex defmodule Mix.Tasks.MyTask do use Mix.Task @shortdoc "A simple mix task" def run(_) do IO.puts "YO!" end end Compile and run: $ mix compile $ mix my_task "YO!" Custom mix task with command line arguments In a basic implementation the task module must define a run/1 function that takes a list of arguments. E.g. def run(args) do ... end defmodule Mix.Tasks.Example_Task do use Mix.Task @shortdoc "Example_Task prints hello + its arguments" def run(args) do IO.puts "Hello #{args}" end end Compile and run: $ mix example_task world "hello world" Aliases Elixir allows you to add aliases for your mix commands. Cool thing if you want to save yourself some typing. Open mix.exs in your Elixir project. First, add aliases/0 function to the keyword list that the project function returns. Adding () at the https://riptutorial.com/ 58 end of the aliases function will prevent compiler from throwing a warning. def project do [app: :my_app, ... aliases: aliases()] end Then, define your aliases/0 function (e.g. at the bottom of your mix.exs file). ... defp aliases do [go: "phoenix.server", trident: "do deps.get, compile, go"] end You can now use $ mix go to run your Phoenix server (if you're running a Phoenix application). And use $ mix trident to tell mix to fetch all dependencies, compile, and run the server. Get help on available mix tasks To list available mix tasks use: mix help To get help on a specific task use mix help task e.g.: mix help cmd Read Mix online: https://riptutorial.com/elixir/topic/3585/mix https://riptutorial.com/ 59 Chapter 28: Modules Remarks Module Names In Elixir, module names such as IO or String are just atoms under the hood and are converted to the form :"Elixir.ModuleName" at compile time. iex(1)> is_atom(IO) true iex(2)> IO == :"Elixir.IO" true Examples List a module's functions or macros The __info__/1 function takes one of the following atoms: • • :functions - Returns a keyword list of public functions along with their arities :macros - Returns a keyword list of public macros along with their arities To list the Kernel module’s functions: iex> Kernel.__info__ :functions [!=: 2, !==: 2, *: 2, +: 1, +: 2, ++: 2, -: 1, -: 2, --: 2, /: 2, <: 2, <=: 2, ==: 2, ===: 2, =~: 2, >: 2, >=: 2, abs: 1, apply: 2, apply: 3, binary_part: 3, bit_size: 1, byte_size: 1, div: 2, elem: 2, exit: 1, function_exported?: 3, get_and_update_in: 3, get_in: 2, hd: 1, inspect: 1, inspect: 2, is_atom: 1, is_binary: 1, is_bitstring: 1, is_boolean: 1, is_float: 1, is_function: 1, is_function: 2, is_integer: 1, is_list: 1, is_map: 1, is_number: 1, is_pid: 1, is_port: 1, is_reference: 1, is_tuple: 1, length: 1, macro_exported?: 3, make_ref: 0, ...] Replace Kernel with any module of your choosing. Using modules Modules have four associated keywords to make using them in other modules: alias, import, use, and require. alias will register a module under a different (usually shorter) name: defmodule MyModule do # Will make this module available as `CoolFunctions` alias MyOtherModule.CoolFunctions # Or you can specify the name to use https://riptutorial.com/ 60 alias MyOtherModule.CoolFunctions, as: CoolFuncs end import will make all the functions in the module available with no name in front of them: defmodule MyModule do import Enum def do_things(some_list) do # No need for the `Enum.` prefix join(some_list, " ") end end use allows a module to inject code into the current module - this is typically done as part of a framework that creates its own functions to make your module confirm to some behaviour. require loads macros from the module so that they can be used. Delegating functions to another module Use defdelegate to define functions that delegate to functions of the same name defined in another module: defmodule Math do defdelegate pi, to: :math end iex> Math.pi 3.141592653589793 Read Modules online: https://riptutorial.com/elixir/topic/2721/modules https://riptutorial.com/ 61 Chapter 29: Nodes Examples List all visible nodes in the system iex(bob@127.0.0.1)> Node.list [:"frank@127.0.0.1"] Connecting nodes on the same machine Start two named nodes in two terminal windows: >iex --name bob@127.0.0.1 iex(bob@127.0.0.1)> >iex --name frank@127.0.0.1 iex(frank@127.0.0.1)> Connect two nodes by instructing one node to connect: iex(bob@127.0.0.1)> Node.connect :"frank@127.0.0.1" true The two nodes are now connected and aware of each other: iex(bob@127.0.0.1)> Node.list [:"frank@127.0.0.1"] iex(frank@127.0.0.1)> Node.list [:"bob@127.0.0.1"] You can execute code on other nodes: iex(bob@127.0.0.1)> greet = fn() -> IO.puts("Hello from #{inspect(Node.self)}") end iex(bob@127.0.0.1)> Node.spawn(:"frank@127.0.0.1", greet) #PID<9007.74.0> Hello from :"frank@127.0.0.1" :ok Connecting nodes on different machines Start a named process on one IP address: $ iex --name foo@10.238.82.82 --cookie chocolate iex(foo@10.238.82.82)> Node.ping :"bar@10.238.82.85" :pong iex(foo@10.238.82.82)> Node.list [:"bar@10.238.82.85"] https://riptutorial.com/ 62 Start another named process on a different IP address: $ iex --name bar@10.238.82.85 --cookie chocolate iex(bar@10.238.82.85)> Node.list [:"foo@10.238.82.82"] Read Nodes online: https://riptutorial.com/elixir/topic/2065/nodes https://riptutorial.com/ 63 Chapter 30: Operators Examples The Pipe Operator The Pipe Operator |> takes the result of an expression on the left and feeds it as the first parameter to a function on the right. expression |> function Use the Pipe Operator to chain expressions together and to visually document the flow of a series of functions. Consider the following: Oven.bake(Ingredients.Mix([:flour, :cocoa, :sugar, :milk, :eggs, :butter]), :temperature) In the example, Oven.bake comes before Ingredients.mix, but it is executed last. Also, it may not be obvious that :temperature is a parameter of Oven.bake Rewriting this example using the Pipe Operator: [:flour, :cocoa, :sugar, :milk, :eggs, :butter] |> Ingredients.mix |> Oven.bake(:temperature) gives the same result, but the order of execution is clearer. Furthermore, it is clear that :temperature is a parameter to the Oven.bake call. Note that when using the Pipe Operator, the first parameter for each function is relocated to before the Pipe Operator, and so the function being called appears to have one fewer parameter. For instance: Enum.each([1, 2, 3], &(&1+1)) # produces [2, 3, 4] is the same as: [1, 2, 3] |> Enum.each(&(&1+1)) Pipe operator and parentheses Parentheses are needed to avoid ambiguity: foo 1 |> bar 2 |> baz 3 https://riptutorial.com/ 64 Should be written as: foo(1) |> bar(2) |> baz(3) Boolean operators There are two kinds of boolean operators in Elixir: • boolean operators (they expect either true or false as their first argument) x or y # true if x is true, otherwise y x and y # false if x is false, otherwise y not x # false if x is true, otherwise true All of booleans operators will raise ArgumentError if first argument won't be strictly boolean value, which means only true or false (nil is not boolean). iex(1)> false and 1 # return false iex(2)> false or 1 # return 1 iex(3)> nil and 1 # raise (ArgumentError) argument error: nil • relaxed boolean operators (work with any type, everything that neither false nor nil is considered as true) x || y # x if x is true, otherwise y x && y # y if x is true, otherwise false !x # false if x is true, otherwise true Operator || will always return first argument if it's truthy (Elixir treats everything except nil and false to be true in comparisions), otherwise will return second one. iex(1)> 1 || 3 # return 1, because 1 is truthy iex(2)> false || 3 # return 3 iex(3)> 3 || false # return 3 iex(4)> false || nil # return nil iex(5)> nil || false # return false Operator && will always return second argument if it's truthy. Otherwise will return respectively to the arguments, false or nil. iex(1)> 1 && 3 # return 3, first argument is truthy iex(2)> false && 3 # return false iex(3)> 3 && false # return false iex(4)> 3 && nil # return nil iex(5)> false && nil # return false iex(6)> nil && false # return nil https://riptutorial.com/ 65 Both && and || are short-circuit operators. They only execute the right side if the left side is not enough to determine the result. Operator ! will return boolean value of negation of current term: iex(1)> !2 # return false iex(2)> !false # return true iex(3)> !"Test" # return false iex(4)> !nil # return true Simple way to get boolean value of selected term is to simply double this operator: iex(1)> !!true # return true iex(2)> !!"Test" # return true iex(3)> !!nil # return false iex(4)> !!false # return false Comparison operators Equality: • • • • value equality x == y (1 == 1.0 # true) value inequality x == y (1 != 1.0 # false) strict equality x === y (1 === 1.0 # false) strict inequality x === y (1 !== 1.0 # true) Comparison: • • • • x > y x >= y x < y x <= y If types are compatible, comparison uses natural ordering. Otherwise there is general types comparison rule: number < atom < reference < function < port < pid < tuple < map < list < binary Join operators You can join (concatenate) binaries (including strings) and lists: iex(1)> [1, 2, 3] ++ [4, 5] [1, 2, 3, 4, 5] iex(2)> [1, 2, 3, 4, 5] -- [1, 3] [2, 4, 5] iex(3)> "qwe" <> "rty" "qwerty" https://riptutorial.com/ 66 'In' operator in operator allows you to check whether a list or a range includes an item: iex(4)> 1 in [1, 2, 3, 4] true iex(5)> 0 in (1..5) false Read Operators online: https://riptutorial.com/elixir/topic/1161/operators https://riptutorial.com/ 67 Chapter 31: Optimization Examples Always measure first! These are general tips that in general improve performance. If your code is slow, it is always important to profile it to figure out what parts are slow. Guessing is never enough. Improving the execution speed of something that only takes up 1% of the execution time probably isn't worth the effort. Look for the big time sinks. To get somewhat accurate numbers, make sure the code you are optimizing is executed for at least one second when profiling. If you spend 10% of the execution time in that function, make sure the complete program execution takes up at least 10 seconds, and make sure you can run the same exact data through the code multiple times, to get repeatable numbers. ExProf is simple to get started with. Read Optimization online: https://riptutorial.com/elixir/topic/6062/optimization https://riptutorial.com/ 68 Chapter 32: Pattern matching Examples Pattern matching functions #You can use pattern matching to run different #functions based on which parameters you pass #This example uses pattern matching to start, #run, and end a recursive function defmodule Counter do def count_to do count_to(100, 0) #No argument, init with 100 end def count_to(counter) do count_to(counter, 0) #Initialize the recursive function end def count_to(counter, value) when value == counter do #This guard clause allows me to check my arguments against #expressions. This ends the recursion when the value matches #the number I am counting to. :ok end def count_to(counter, value) do #Actually do the counting IO.puts value count_to(counter, value + 1) end end Pattern matching on a map %{username: username} = %{username: "John Doe", id: 1} # username == "John Doe" %{username: username, id: 2} = %{username: "John Doe", id: 1} ** (MatchError) no match of right hand side value: %{id: 1, username: "John Doe"} Pattern matching on a list You can also pattern match on Elixir Data Structures such as Lists. Lists Matching on a list is quite simple. https://riptutorial.com/ 69 [head | tail] = [1,2,3,4,5] # head == 1 # tail == [2,3,4,5] This works by matching the first (or more) elements in the list to the left hand side of the | (pipe) and the rest of the list to the right hand side variable of the |. We can also match on specific values of a list: [1,2 | tail] = [1,2,3,4,5] # tail = [3,4,5] [4 | tail] = [1,2,3,4,5] ** (MatchError) no match of right hand side value: [1, 2, 3, 4, 5] Binding multiple consecutive values on the left of the | is also allowed: [a, b | tail] = [1,2,3,4,5] # a == 1 # b == 2 # tail = [3,4,5] Even more complex - we can match on a specific value, and match that against a variable: iex(11)> [a = 1 | tail] = [1,2,3,4,5] # a == 1 Get the sum of a list using pattern matching defmodule Math do # We start of by passing the sum/1 function a list of numbers. def sum(numbers) do do_sum(numbers, 0) end # Recurse over the list when it contains at least one element. # We break the list up into two parts: # head: the first element of the list # tail: a list of all elements except the head # Every time this function is executed it makes the list of numbers # one element smaller until it is empty. defp do_sum([head|tail], acc) do do_sum(tail, head + acc) end # When we have reached the end of the list, return the accumulated sum defp do_sum([], acc), do: acc end Anonymous functions f = fn {:a, :b} -> IO.puts "Tuple {:a, :b}" https://riptutorial.com/ 70 [] -> IO.puts "Empty list" end f.({:a, :b}) # Tuple {:a, :b} f.([]) # Empty list Tuples { a, b, c } = { "Hello", "World", "!" } IO.puts a # Hello IO.puts b # World IO.puts c # ! # Tuples of different size won't match: { a, b, c } = { "Hello", "World" } # (MatchError) no match of right hand side value: { "Hello", "World" } Reading a File Pattern matching is useful for an operation like file reading which returns a tuple. If the file sample.txt contains This is a sample text, then: { :ok, file } = File.read("sample.txt") # => {:ok, "This is a sample text"} file # => "This is a sample text" Otherwise, if the file does not exist: { :ok, file } = File.read("sample.txt") # => ** (MatchError) no match of right hand side value: {:error, :enoent} { :error, msg } = File.read("sample.txt") # => {:error, :enoent} Pattern matching anonymous functions fizzbuzz = fn (0, 0, _) -> "FizzBuzz" (0, _, _) -> "Fizz" (_, 0, _) -> "Buzz" (_, _, x) -> x end my_function = fn(n) -> fizzbuzz.(rem(n, 3), rem(n, 5), n) end https://riptutorial.com/ 71 Read Pattern matching online: https://riptutorial.com/elixir/topic/1602/pattern-matching https://riptutorial.com/ 72 Chapter 33: Polymorphism in Elixir Introduction Polymorphism is the provision of a single interface to entities of different types. Basically, it allows different data types respond to the same function. So, the same function shapes for different data types to accomplish the same behavior. Elixir language has protocols to implement polymorphism with a clean way. Remarks If you want to cover all data types you can define an implementation for Any data type. Lastly, if you have time, check the source code of Enum and String.Char, which are good examples of polymorphism in core Elixir. Examples Polymorphism with Protocols Let's implement a basic protocol that converts Kelvin and Fahrenheit temperatures to Celsius. defmodule Kelvin do defstruct name: "Kelvin", symbol: "K", degree: 0 end defmodule Fahrenheit do defstruct name: "Fahrenheit", symbol: "°F", degree: 0 end defmodule Celsius do defstruct name: "Celsius", symbol: "°C", degree: 0 end defprotocol Temperature do @doc """ Convert Kelvin and Fahrenheit to Celsius degree """ def to_celsius(degree) end defimpl Temperature, for: Kelvin do @doc """ Deduct 273.15 """ def to_celsius(kelvin) do celsius_degree = kelvin.degree - 273.15 %Celsius{degree: celsius_degree} end end defimpl Temperature, for: Fahrenheit do https://riptutorial.com/ 73 @doc """ Deduct 32, then multiply by 5, then divide by 9 """ def to_celsius(fahrenheit) do celsius_degree = (fahrenheit.degree - 32) * 5 / 9 %Celsius{degree: celsius_degree} end end Now, we implemented our converters for the Kelvin and Fahrenheit types. Let's make some conversions: iex> fahrenheit = %Fahrenheit{degree: 45} %Fahrenheit{degree: 45, name: "Fahrenheit", symbol: "°F"} iex> celsius = Temperature.to_celsius(fahrenheit) %Celsius{degree: 7.22, name: "Celsius", symbol: "°C"} iex> kelvin = %Kelvin{degree: 300} %Kelvin{degree: 300, name: "Kelvin", symbol: "K"} iex> celsius = Temperature.to_celsius(kelvin) %Celsius{degree: 26.85, name: "Celsius", symbol: "°C"} Let's try to convert any other data type which has no implementation for to_celsius function: iex> Temperature.to_celsius(%{degree: 12}) ** (Protocol.UndefinedError) protocol Temperature not implemented for %{degree: 12} iex:11: Temperature.impl_for!/1 iex:15: Temperature.to_celsius/1 Read Polymorphism in Elixir online: https://riptutorial.com/elixir/topic/9519/polymorphism-in-elixir https://riptutorial.com/ 74 Chapter 34: Processes Examples Spawning a Simple Process In the following example, the greet function inside Greeter module is run in a separate process: defmodule Greeter do def greet do IO.puts "Hello programmer!" end end iex> spawn(Greeter, :greet, []) Hello #PID<0.122.0> Here #PID<0.122.0> is the process identifier for the spawned process. Sending and Receiving Messages defmodule Processes do def receiver do receive do {:ok, val} -> IO.puts "Received Value: #{val}" _ -> IO.puts "Received something else" end end end iex(1)> pid = spawn(Processes, :receiver, []) #PID<0.84.0> iex(2)> send pid, {:ok, 10} Received Value: 10 {:ok, 10} Recursion and Receive Recursion can be used to receive multiple messages defmodule Processes do def receiver do receive do {:ok, val} -> IO.puts "Received Value: #{val}" _ -> IO.puts "Received something else" end https://riptutorial.com/ 75 receiver end end iex(1)> pid = spawn Processes, :receiver, [] #PID<0.95.0> iex(2)> send pid, {:ok, 10} Received Value: 10 {:ok, 10} iex(3)> send pid, {:ok, 42} {:ok, 42} Received Value: 42 iex(4)> send pid, :random :random Received something else Elixir will use a tail-call recursion optimisation as long as the function call is the last thing that happens in the function as it is in the example. Read Processes online: https://riptutorial.com/elixir/topic/3173/processes https://riptutorial.com/ 76 Chapter 35: Protocols Remarks A note on structs Instead of sharing protocol implementation with maps, structs require their own protocol implementation. Examples Introduction Protocols enable polymorphism in Elixir. Define protocols with defprotocol: defprotocol Log do def log(value, opts) end Implement a protocol with defimpl: require Logger # User and Post are custom structs defimpl Log, for: User do def log(user, _opts) do Logger.info "User: #{user.name}, #{user.age}" end end defimpl Log, for: Post do def log(user, _opts) do Logger.info "Post: #{post.title}, #{post.category}" end end With the above implementations, we can do: iex> Log.log(%User{name: "Yos", age: 23}) 22:53:11.604 [info] User: Yos, 23 iex> Log.log(%Post{title: "Protocols", category: "Protocols"}) 22:53:43.604 [info] Post: Protocols, Protocols Protocols let you dispatch to any data type, so long as it implements the protocol. This includes some built-in types such as Atom, BitString, Tuples, and others. Read Protocols online: https://riptutorial.com/elixir/topic/3487/protocols https://riptutorial.com/ 77 Chapter 36: Sigils Examples Build a list of strings iex> ~w(a b c) ["a", "b", "c"] Build a list of atoms iex> ~w(a b c)a [:a, :b, :c] Custom sigils Custom sigils can be made by creating a method sigil_X where X is the letter you want to use (this can only be a single letter). defmodule Sigils do def sigil_j(string, options) do # Split on the letter p, or do something more useful String.split string, "p" end # Use this sigil in this module, or import it to use it elsewhere end The options argument is a binary of the arguments given at the end of the sigil, for example: ~j/foople/abc # string is "foople", options are 'abc' # ["foo", "le"] Read Sigils online: https://riptutorial.com/elixir/topic/2204/sigils https://riptutorial.com/ 78 Chapter 37: State Handling in Elixir Examples Managing a piece of state with an Agent The simplest way to wrap and access a piece of state is Agent. The module allows one to spawn a process that keeps an arbitrary data structure and allows one to send messages to read and update that structure. Thanks to this the access to the structure is automatically serialized, as the process only handles one message at a time. iex(1)> {:ok, pid} = Agent.start_link(fn -> :initial_value end) {:ok, #PID<0.62.0>} iex(2)> Agent.get(pid, &(&1)) :initial_value iex(3)> Agent.update(pid, fn(value) -> {value, :more_data} end) :ok iex(4)> Agent.get(pid, &(&1)) {:initial_value, :more_data} Read State Handling in Elixir online: https://riptutorial.com/elixir/topic/6596/state-handling-in-elixir https://riptutorial.com/ 79 Chapter 38: Stream Remarks Streams are composable, lazy enumerables. Due to their laziness, streams are useful when working with large (or even infinite) collections. When chaining many operations with Enum, intermediate lists are created, while Stream creates a recipe of computations that are executed at a later moment. Examples Chaining multiple operations Stream is especially useful when you want to run multiple operations on a collection. This is because Stream is lazy and only does one iteration (whereas Enum would do multiple iterations, for example). numbers = 1..100 |> Stream.map(fn(x) -> x * 2 end) |> Stream.filter(fn(x) -> rem(x, 2) == 0 end) |> Stream.take_every(3) |> Enum.to_list [2, 8, 14, 20, 26, 32, 38, 44, 50, 56, 62, 68, 74, 80, 86, 92, 98, 104, 110, 116, 122, 128, 134, 140, 146, 152, 158, 164, 170, 176, 182, 188, 194, 200] Here, we chained 3 operations (map, filter and take_every), but the final iteration was only done after Enum.to_list was called. What Stream does internally, is that it waits until actual evaluation is required. Before that, it creates a list of all the functions, but once evaluation is needed, it does goes through the collection once, running all the functions on every item. This makes it more efficient than Enum, which in this case would do 3 iterations, for example. Read Stream online: https://riptutorial.com/elixir/topic/2553/stream https://riptutorial.com/ 80 Chapter 39: Strings Remarks A String in Elixir is a UTF-8 encoded binary. Examples Convert to string Use Kernel.inspect to convert anything to string. iex> Kernel.inspect(1) "1" iex> Kernel.inspect(4.2) "4.2" iex> Kernel.inspect %{pi: 3.14, name: "Yos"} "%{pi: 3.14, name: \"Yos\"}" Get a substring iex> my_string = "Lorem ipsum dolor sit amet, consectetur adipiscing elit." iex> String.slice my_string, 6..10 "ipsum" Split a string iex> String.split("Elixir, Antidote, Panacea", ",") ["Elixir", "Antidote", "Panacea"] String Interpolation iex(1)> name = "John" "John" iex(2)> greeting = "Hello, #{name}" "Hello, John" iex(3)> num = 15 15 iex(4)> results = "#{num} item(s) found." "15 item(s) found." Check if String contains Substring iex(1)> String.contains? "elixir of life", "of" true iex(2)> String.contains? "elixir of life", ["life", "death"] true https://riptutorial.com/ 81 iex(3)> String.contains? "elixir of life", ["venus", "mercury"] false Join Strings You can concatenate strings in Elixir using the <> operator: "Hello" <> "World" # => "HelloWorld" For a List of Strings, you can use Enum.join/2: Enum.join(["A", "few", "words"], " ") # => "A few words" Read Strings online: https://riptutorial.com/elixir/topic/2618/strings https://riptutorial.com/ 82 Chapter 40: Task Syntax • • Task.async(fun) Task.await(task) Parameters Parameter Details fun task The function that should be executed in a separate process. The task returned by Task.async. Examples Doing work in the background task = Task.async(fn -> expensive_computation end) do_something_else result = Task.await(task) Parallel processing crawled_site = ["http://www.google.com", "http://www.stackoverflow.com"] |> Enum.map(fn site -> Task.async(fn -> crawl(site) end) end) |> Enum.map(&Task.await/1) Read Task online: https://riptutorial.com/elixir/topic/7588/task https://riptutorial.com/ 83 Chapter 41: Tips and Tricks Introduction Elixir Advanced tips and tricks which save our time while coding. Examples Creating Custom Sigils and Documenting Each x sigil call respective sigil_x definition Defining Custom Sigils defmodule MySigils do #returns the downcasing string if option l is given then returns the list of downcase letters def sigil_l(string,[]), do: String.Casing.downcase(string) def sigil_l(string,[?l]), do: String.Casing.downcase(string) |> String.graphemes #returns the upcasing string if option l is given then returns the list of downcase letters def sigil_u(string,[]), do: String.Casing.upcase(string) def sigil_u(string,[?l]), do: String.Casing.upcase(string) |> String.graphemes end Multiple [ OR ] This is just the other way of writing Multiple OR conditions. This is not the recommended approach because in regular approach when the condition evaluates to true, it stops executing the remaining conditions which save the time of evaluation, unlike this approach which evaluates all conditions first in the list. This is just bad but good for discoveries. # Regular Approach find = fn(x) when x>10 or x<5 or x==7 -> x end # Our Hack hell = fn(x) when true in [x>10,x<5,x==7] -> x end iex Custom Configuration - iex Decoration Copy the content into a file and save the file as .iex.exs in your ~ home directory and see the magic. You can also download the file HERE # IEx.configure colors: [enabled: true] # IEx.configure colors: [ eval_result: [ :cyan, :bright ] ] IO.puts IO.ANSI.red_background() <> IO.ANSI.white() <> " ❄❄❄ Good Luck with Elixir ❄❄❄ " <> IO.ANSI.reset Application.put_env(:elixir, :ansi_enabled, true) IEx.configure( https://riptutorial.com/ 84 colors: [ eval_result: [:green, :bright] , eval_error: [[:red,:bright,"Bug Bug ..!!"]], eval_info: [:yellow, :bright ], ], default_prompt: [ "\e[G", # ANSI CHA, move cursor to column 1 :white, "I", :red, "❤" , # plain string :green, "%prefix",:white,"|", :blue, "%counter", :white, "|", :red, "▶" , # plain string :white, "▶▶" , # plain string # ❤ ❤-»" , # plain string :reset ] |> IO.ANSI.format |> IO.chardata_to_string ) Read Tips and Tricks online: https://riptutorial.com/elixir/topic/10623/tips-and-tricks https://riptutorial.com/ 85 Credits S. No Chapters Contributors Getting started with Elixir Language alejosocorro, Andrey Chernykh, Ben Bals, Community, cwc, Delameko, Douglas Correa, helcim, I Am Batman, JAlberto, koolkat, leifg, MattW., rap-2-h, Simone Carletti, Stephan Rodemeier, Vinicius Quaiato, Yedhu Krishnan, Zimm i48 Basic .gitignore for elixir program Yos Riady basic use of guard clauses alxndr BEAM Yos Riady Behaviours Yos Riady Better debugging with IO.inspect and labels leifg Built-in types Conditionals Andrey Chernykh, Arithmeticbird, Oskar, TreyE, Vinicius Quaiato Andrey Chernykh, evuez, javanut13, Musfiqur Rahman, Paweł Obrok Constants ibgib 1 2 3 4 5 6 7 8 9 10 Data Structures Sam Mercier, Simone Carletti, Stephan Rodemeier, Yos Riady 11 Debugging Tips javanut13, Paweł Obrok, Pfitz, Philippe-Arnaud de MANGOU, sbs 12 Doctests aholt, milmazz, Philippe-Arnaud de MANGOU, Yos Riady 13 Ecto 14 Erlang 15 ExDoc 16 ExUnit fgutierr, Philippe-Arnaud de MANGOU, toraritte 4444, Yos Riady milmazz, Yos Riady Yos Riady 17 Functional Dinesh Balasubramanian https://riptutorial.com/ 86 programming in Elixir 18 Functions Andrey Chernykh, cwc, Dair, Eiji, Filip Haglund, PatNowak, rainteller, Simone Carletti, Stephan Rodemeier, Yedhu Krishnan , Yos Riady 19 20 Getting help in IEx console helcim IEx Console Tips & Tricks alxndr, Cifer, fahrradflucht, legoscia, mudasobwa, muttonlamb, PatNowak, Paweł Obrok, sbs, Sheharyar, Simone Carletti, Stephan Rodemeier, Uniaika, Vincent, Yos Riady 21 Installation cwc, Douglas Correa, Eiji, JAlberto, MattW. 22 Join Strings Agung Santoso 23 Lists Ben Bals, Candy Gumdrop, emoragaf, PatNowak, Sheharyar, Yos Riady 24 Maps and Keyword Lists Sam Mercier, Simone Carletti, Yos Riady 25 Metaprogramming 4444, Paweł Obrok 26 Mix 4444, helcim, rainteller, Slava.K, Yos Riady 27 Modules Alex G, javanut13, Yos Riady 28 Nodes Yos Riady 29 Operators alxndr, Andrey Chernykh, Dair, Gazler, Mitkins, nirev, PatNowak 30 Optimization Filip Haglund, legoscia 31 Pattern matching Alex Anderson, Dair, Danny Rosenblatt, evuez, Gabriel C, gmile , Harrison Lucas, javanut13, Oskar, PatNowak, theIV, Thomas, Yedhu Krishnan 32 Polymorphism in Elixir mustafaturan 33 Processes Alex G, Yedhu Krishnan 34 Protocols Yos Riady 35 Sigils javanut13, Yos Riady 36 State Handling in Elixir Paweł Obrok https://riptutorial.com/ 87 37 Stream Oskar 38 Strings Alex G, Sheharyar, Yos Riady 39 Task mario 40 Tips and Tricks Ankanna https://riptutorial.com/ 88