How do you specify a function as a parameter to another function in Elixir? For instance, pass foo to bar so that bar can then call foo. What is the syntax both in the calling function and the function that receives it?

How do you pass a function as a parameter in Elixir?

I&#39;m pretty new in Elixir, but have a lot fun with it! 

I came from Ruby world, so start looking analogy. And there is exist debugging tool `pry`. Using `binding.pry` I can interrupt any session. I found something similar in Elixir – `IEx.pry`. But it doesn&#39;t work when I&#39;m testing something through `ExUnit`. 

Question – is it is possible to interrupt testing session and run iex with current environment?

Pry while testing

I&#39;m just starting out with Elixir. I&#39;m writing some tests using ExUnit for simple Enumerable functions that I am implementing myself, without using the standard Enum module.

In my tests I&#39;m finding that whenever I reference the list `[7, 8, 9]`, once it is printed in in stdout I am seeing the char list `&#39;\a\b\t&#39;`. Why does this sort of thing happen?

Elixir lists interpreted as char lists

I was trying to add a new element into a list as follow:

    iex(8)&gt; l = [3,5,7,7,8] ++ 3
    [3, 5, 7, 7, 8 | 3]
    iex(9)&gt; l
    [3, 5, 7, 7, 8 | 3]

Why did I get on the 5th position like

    8 | 3

What it does mean?  
And how can I add new element to the list?

--------**Update**--------  
I try to loop the list as follow:

    iex(2)&gt; l = [1,2] ++ 3
    [1, 2 | 3]
    iex(3)&gt; Enum.each(l, fn(x) -&gt; IO.puts(x) end)
    1
    2
    ** (FunctionClauseError) no function clause matching in Enum.&quot;-each/2-lists^foreach/1-0-&quot;/2
        (elixir) lib/enum.ex:604: Enum.&quot;-each/2-lists^foreach/1-0-&quot;(#Function&lt;6.54118792/1 in :erl_eval.expr/5&gt;, 3)
        (elixir) lib/enum.ex:604: Enum.each/2

Since the pointer of the number 2 is not pointing to a list, rather to value 3, how can I loop the list?

Add new element to list

I&#39;m learning Elixir and wonder why it has two types of function definitions:

 - functions defined in a module with `def`, called using `myfunction(param1, param2)`
 - anonymous functions defined with `fn`, called using `myfn.(param1, param2)`

Only the second kind of function seems to be a first-class object and can be passed as a parameter to other functions. A function defined in a module needs to be wrapped in a `fn`. There&#39;s some syntactic sugar which looks like `otherfunction(&amp;myfunction(&amp;1, &amp;2))` in order to make that easy, but why is it necessary in the first place? Why can&#39;t we just do `otherfunction(myfunction))`? Is it only to allow calling module functions without parenthesis like in Ruby? It seems to have inherited this characteristic from Erlang which also has module functions and funs, so does it actually comes from how the Erlang VM works internally?

It there any benefit having two types of functions and converting from one type to another in order to pass them to other functions? Is there a benefit having two different notations to call functions?

Why are there two kinds of functions in Elixir?

How can I make Mix run only specific tests from my suite of tests?

When running `mix test` all tests are executed

How can I make Mix run only specific tests from my suite of tests?

In the Phoenix router is there a route that could act as a wildcard?




Catch-all/wildcard route in Elixir&#39;s Phoenix?

In elixir 1.2 they&#39;ve included the keyword &quot;with&quot;, but it&#39;s not completely clear to me what it is for.

How and in which situation would I use it?


How to use the &quot;with&quot; keyword in Elixir and what is it for?

How to do the similar conditional one-line check in Elixir?

```lang-elixir
if (x &gt; 0) ? x : nil
```

Is this the only equivalent in elixir world?

```lang-elixir
if true, do: 1, else: 2
```

Simulate ternary operator in Elixir

In Ruby, if one were defining constants in classes, they would define them using all caps. For example:

    class MyClass
      MY_FAVORITE_NUMBER = 13
    end

How do you do this in Elixir? And if no such equivalent exists, how do you get around the problem of magic numbers in Elixir?

How do you define constants in Elixir modules?

I&#39;m trying to format a Postgres date representation into a ISO 8601 string. I&#39;m assuming that there is a Postgres function that can do it, but I found the documentation short on examples. 

My query is 

    SELECT
      now()::timestamp

which returns

    [{{2016, 8, 9}, {3, 56, 55, 754181}}]

I&#39;m trying to get the date into a format that looks more like 
`2016-8-9T03:56:55+00:00`. 

What changes do I need to make to my query to make that happen? Thanks for your help.

Turn postgres date representation into ISO 8601 string

How can I connect two Erlang/Elixir-nodes of two different machines via network connection?

How to connect two Elixir nodes via local network?

I am trying to grasp the difference between **Lists** and **Tuples** in `Elixir`. From the [**Basic Types**](http://elixir-lang.org/getting-started/basic-types.html#lists-or-tuples) section of Elixir Guides, I understand that:

 - Lists are stored as Linked Items
 - Updating a List is fast (only when prepending)
 - Fetching List items is slow
 - Fetching List information (size/length) is slow
 - Tuple Elements are stored together
 - Getting Tuple information is fast
 - Fetching Tuple elements is fast
 - Modifying Tuples is expensive

---

Okay, that&#39;s all fine but **I&#39;m still not sure what to use when**. I see that most of the methods return a tuple but everywhere else Lists are used, and many methods accept Lists as input, not tuples. By the stated points above, shouldn&#39;t Tuples be used for passing data around, since reading from a tuple of user-given values would be fast?

I also noticed Tuples aren&#39;t enumerable, what&#39;s up with that? Wouldn&#39;t using `Enum` over them be faster than using it on Lists?

If someone could help me understand them better, possibly by giving a few examples of what to use when, that&#39;d be awesome.

Lists vs. Tuples - What to use and when?

I&#39;d like to set the title of my app in `my/config/config.exs` file:

    config :my, My.Endpoint,
      url: [host: &quot;localhost&quot;],
      root: Path.dirname(__DIR__),
      secret_key_base: &quot;secret&quot;,
      title: &quot;My App&quot;

How can I read `title` later to use it in template? Something like:

    &lt;div&gt;
      Title of my app is &lt;%= ??? %&gt;
    &lt;/div&gt;

I tried `conn.title` and it says there&#39;s no such key. But, when I try `conn.secret_key_base` it works. Why?

How to read config variable in Phoenix / Elixir?

Does anyone know of (or can provide) an example of how to alter a table column name using the ecto DSL

I&#39;m guessing I just use mix ecto.gen.migration but then would I just fill in the empty created file with my custom code (if so, how would you edit a column name, the docs show modify to change the column type)

or is there a command line flag I can pass to generate the migration code for me?

How to alter a column name in an Ecto model with a migration?

I&#39;m trying to convert a struct to a map to be able to clean all the nil values

I&#39;m currently using this code 


	  case Nadia.get_updates  do
	    {:ok, results} -&gt;
		  Map.from_struct(results)
		  |&gt; Enum.filter(fn {_, v} -&gt; v != nil end)
		  |&gt; Enum.into(%{})

Note: Nadia.get_updates returns the following structure:
https://hexdocs.pm/nadia/Nadia.Model.Update.html#t:t/0

Yet I&#39;m always receiving the following error: no function clause matching in Map.from_struct/1


Elixir convert struct to map

Behaviours define callbacks &amp; protocols define methods without signatures. Modules implementing a protocol should give definition for all those methods. Same for modules using a behaviour. What is the semantic difference? 

One difference I can think of is, a protocol can be implemented for a single type only once where as we can implement a behaviour for a module multiple times based on our requirements. I am clear with when to use what. Is there any other difference other than this?

Difference between protocol &amp; behaviour in elixir

I have an upsert requirement, so I need to call a postgres stored procedure or use a common table expression.  I also use the pgcrypto exgtension for passwords and would like to use postgres functions (such as &quot;crypt&quot; to encode/decode passwords).

But I can not find a way to get Ecto to play with raw sql in part or whole, is it intended that ecto will only support the elixir dsl and not allow shelling out to raw sql when the dsl is not sufficient?

I&#39;ve found that I can query via the adapter (Rocket is the name of the app)

    q = Ecto.Adapters.Postgres.query(Rocket.Repo,&quot;select * from users limit 1&quot;,[])

But not sure how to get this to the model.  I&#39;m new to elixir and it seems I should be able to use Ecto.Model.Schem.__schema__/3 but this fails

    Rocket.User.__schema__(:load,q.rows |&gt; List.first,0)
    ** (FunctionClauseError) no function clause matching in Rocket.User.__schema__/3    

How to use raw sql with ecto Repo

So let&#39;s say I want to send a bunch of emails or recreate sitemap or whatever every 4 hours, how would I do that in Phoenix or just with Elixir? 


How can I schedule code to run every few hours in Elixir or Phoenix framework?

How do I join two strings in a list with a space, like:

    [&quot;StringA&quot;, &quot;StringB&quot;]

becomes

    &quot;StringA StringB&quot;



How to join strings in Elixir?

In Elixir how do you check for type such as in Python:

    &gt;&gt;&gt; a = &quot;test&quot;
    &gt;&gt;&gt; type(a)
    &lt;type &#39;str&#39;&gt;
    &gt;&gt;&gt; b =10
    &gt;&gt;&gt; type(b)
    &lt;type &#39;int&#39;&gt;

I read in Elixir there are type checkers such as &#39;is_bitstring&#39;, &#39;is_float&#39;, &#39;is_list&#39;, &#39;is_map&#39; etc, but what if you have no idea what the type could be ?

How do you check for the type of variable in Elixir

What&#39;s the difference between `use` and `import`?

&gt; use is a simple mechanism for using a given module into the current context

https://hexdocs.pm/elixir/Kernel.SpecialForms.html#import/2

&gt; Imports function and macros from other modules

Looks like one difference is `import` let&#39;s you pick out the specific functions/macros whereas `use` brings everything in.

Are there other differences? When would you use one over the other?

Elixir: use vs import

Lately I&#39;ve been doing some experiments with docker compose in order to deploy multiple collaborating microservices. I can see the many benefits that microservices provide, and now that there is a good toolset for managing them, I think that it&#39;s not extremely hard to jump into the microservices wagon.

But, I have been experimenting with Elixir too, and I am quite fond of the benefits that provides by itself. Given that it encourages packing your code into multiple decoupled applications, and supports hot code upgrades, how would you mix docker with elixir (or erlang, for that matter)?

For example, if I want to use docker because it provides dev-prod parity, how does elixir fit in that? Given that docker containers are immutable, I lose the ability to do hot-code upgrades, right? What about blue/green deployments or canary releases?

I mean, I could just write microservices with Elixir and use them as if they were written in any other language, polyglotism is one of the benefits of microservices anyway, but then I&#39;m not getting the full benefits of using the OTP platform, I guess that pure collaborative erlang applications are way more optimal that using intermediate queues to communicate between microservices written in different (or not) languages.

Where does Elixir/erlang fit into the microservices approach?

This question is in the context of the Beam VM and the capabilities that it provides, not in the general context of what a Turing complete language can do. I want to invest some time to learn either pure Erlang or Elixir. I get the basic differences between the two and I am leaning towards Elixir because of the macros, better syntax and faster development of the language this day.

My question is: if I choose Elixir, will I stumble on something that I cannot do in it, but can do in Erlang? Can I use all the OTP stuff, all the Erlang libraries, code reload, etc. with Elixir?

I am not asking for someone&#39;s preference between the two; just facts about the possibilities of the languages. Preferably from someone who used both in production.


Are there things Elixir can do that Erlang cannot, or vice versa?

I need to convert a string to a floating point value or an integer. There was no method such as,

    string_to_integer



Convert Elixir string to integer or float

In elixir we have Maps:

    &gt; map = %{:a =&gt; &quot;one&quot;, :b =&gt; &quot;two&quot;} # = %{a: &quot;one&quot;, b: &quot;two&quot;}
    &gt; map.a                             # = &quot;one&quot;
    &gt; map[:a]                           # = &quot;one&quot;

We also have Keyword Lists:

    &gt; kl = [a: &quot;one&quot;, b: &quot;two&quot;]       # = [a: &quot;one&quot;, b: &quot;two&quot;]
    &gt; kl2 = [{:a, &quot;one&quot;},{:b, &quot;two&quot;}] # = [a: &quot;one&quot;, b: &quot;two&quot;]
    &gt; kl == kl2                       # = true
    &gt; kl[:a]                          # = &quot;one&quot;
    &gt; kl.a                            # = ** (ArgumentError)

Why both?  

**Syntax?** Is it because Keyword Lists have a more flexible syntax allowing them to be defined without curlys and even without brackets as the last param of a function call? Then why not give Maps this syntactic sugar?

**Duplicate Keys?** Is it because Keyword Lists can have duplicate keys? Why would you want both Map style access and duplicate keys?

**Performance?** Is it because Keyword Lists have better performance? Then why have Maps? And shouldn&#39;t maps be more performant at looking up members by key than a list of tuples?

**JS Array and Ruby Hash like appearance?** Is that it?

I understand that structurally they are different data representations. To me it seems that Keyword Lists in elixir serve to complicate the language through exceptional syntax (3 different syntactic variants), use case overlap with maps, and an unclear benefit.

What is the benefit of using Keyword Lists?

What is the benefit of Keyword Lists?

I&#39;m just learning Phoenix and Elixir and I&#39;m coming from Ruby/Rails where I work in the REPL using `pry` to inspect my database and application state.

I&#39;m trying to figure out how to interact with my database and models in a Phoenix app. I&#39;m aware of `iex`, but I don&#39;t know how to use it inspect my app&#39;s database from the repl. Do I need to connect to it with ecto each time from the repl? Is there a `rails console` equivalent. I&#39;ve checked the Phoenix docs, Elixir Dose, and the Ecto repo, but can&#39;t find what I&#39;m looking for. Am I missing something?

Edit: Based on the answer below I found [this][1] section of the ecto docs. Based on this I can do something like `ArticlesApi.Repo.all ArticlesApi.Article`


  [1]: http://www.phoenixframework.org/v0.6.2/docs/ecto-models#section-experiments-with-our-model

Is there a Phoenix equivalent to Rails Console

This is seemingly simple, but I can&#39;t seem to find it in the docs. I need to simply return `true` or `false` if an item exists in a list or tuple. Is `Enum.find/3` really the best way to do this?

    Enum.find([&quot;foo&quot;, &quot;bar&quot;], &amp;(&amp;1 == &quot;foo&quot;)) != nil


How to check if an item exists in an Elixir list or tuple?

This seems like a really dumb question but how does one get and display the current date or time in Elixir? I tried going through [the docs][1] but couldn&#39;t find anything. Do I need to use an Erlang function?


  [1]: https://hexdocs.pm/elixir/ &quot;Elixir 1.4 documentation&quot;

Getting the current date and or time in Elixir

When I use IEx and make a typo like additional bracket or &quot;, then most of the time I get a syntax error. But there are cases like this one: 
   
    iex(3)&gt; Enum.each &#39;12345&#39;, &amp;(IO.puts(&amp;1&quot;))    
    ...(3)&gt; end   
    ...(3)&gt; )   
    ...(3)&gt; &#39;    
    ...(3)&gt; end    
    ...(3)&gt; &quot;&quot;    
    ...(3)&gt; ... ? How to produce syntax error ?    
    ...(3)&gt;     
    BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded    
          (v)ersion (k)ill (D)b-tables (d)istribution   


I cannot make a syntax error and continue from scratch and I have to relaunch entire IEx.
Is there any keyboard shortcut or command to skip performing current iex(3) and go to next iex(4)?
 

IEx - How to cancel multiline command?

What is the correct way to run an Elixir application?

I&#39;m creating a simple project by:

    mix new app

and after that I can do:

    mix run

which basically compiles my app once. So when I add:

    IO.puts &quot;running&quot;

in `lib/app.ex` I see `&quot;running&quot;` only for the first time, each consecutive `run` does nothing unless there are some changes. What can I do next with generated `app.app`?

Of course I know I can do:

    escript: [main_module: App]

in `mix.exs`, provide `def main(args):` and then:

    mix escript.build
    ./app

but&#39;s it&#39;s kinda cumbersome in my opinion.

There&#39;s also something like:

    elixir lib/app.exs

but it does not count `mix.exs` obviously, which is needed for dependencies in my `app`.

How to run an Elixir application?

Elixir&#39;s documentation [states](https://elixir-lang.org/getting-started/modules-and-functions.html#scripted-mode) that

&gt; In addition to the Elixir file extension .ex, Elixir also supports
&gt; .exs files for scripting. Elixir treats both files exactly the same
&gt; way, the only difference is in intention. .ex files are meant to be
&gt; compiled while .exs files are used for scripting, without the need for
&gt; compilation.

But I&#39;m still not sure when to use which file type. What are the downsides and the purpose of .ex and .exs?

Elixir: When to use .ex and when .exs files

What is the way to convert `%{&quot;foo&quot; =&gt; &quot;bar&quot;}` to `%{foo: &quot;bar&quot;}` in Elixir?

How to convert map keys from strings to atoms in Elixir

I&#39;m going through the Programming Phoenix book and I am wondering what the difference between `def` and `defp` is.

There are several functions in my controller - most of them are actions like this:

    def new (conn, _params) do
    ...
    end

The book had me create another function in this controller that is not a typical controller action like this:

    defp user_videos(user) do
    ...
    end

So my question is how do I know when to use `defp` and when to use `def` when defining a function in Elixir? 

What&#39;s the difference between `def` and `defp`

I need to generate a random number. I found the [`Enum.random/1`](https://hexdocs.pm/elixir/Enum.html#random/1) function, but it expects an enumerable such as a list or range of numbers.

Is that the only way to get a random number?

How to generate a random number in Elixir?

I want to execute a program through my Elixir code. What is the method to call a shell command to a given string? Is there anything which isn&#39;t platform specific?

Run shell commands in Elixir

In Dave Thomas&#39;s book Programming Elixir he states &quot;Elixir enforces immutable data&quot; and goes on to say: 

&gt; In Elixir, once a variable references a list such as [1,2,3], you know it will always reference those same values (until you rebind the variable).

This sounds like &quot;it won&#39;t ever change unless you change it&quot; so I&#39;m confused as to what the difference between mutability and rebinding is. An example highlighting the differences would be really helpful. 

Are Elixir variables really immutable?

I know its possible to create a struct via `%User{ email: &#39;blah@blah.com&#39; }`. But if I had a variable `params = %{email: &#39;blah@blah.com&#39;}` is there a way to create that struct using that variable for eg, `%User{ params }`.

This gives an error, just wondering if you can explode it or some other way?


In Elixir how do you initialize a struct with a map variable

How to sleep / wait for one second?

Best I could find was something like this (in iex):

    IO.puts &quot;foo&quot; ; :timer.sleep(1); IO.puts &quot;bar&quot;

But both of my puts happen with no delay.

Elixir Sleep / Wait for 1 Second

How can I calculate a number with an exponent in Elixir?

For example, 2&lt;sup&gt;3&lt;/sup&gt; would return 8.

How do I raise a number to a power in Elixir?

What would be an elegant way for converting a list of two item tuples like ```[{1,2},{3,4}]``` into the map ```%{1=&gt;2, 3=&gt;4}```?

Keyword list would be trivial, but what if we have arbitrary keys?

How to create a map from a list of two item tuples in Elixir

I am looking for an IDE that does atleast some of the following

 - Code completion when typing variable names and possible
   functions after pressing `.`
 - Show a functions signature and docs
 - Navigate to the function/variable/module&#39;s definition

It would be nice if it could also

 - Warn about errors
 - Code generation
 - Scaffold basic projects

Good IDE for Elixir

In the same way that we can get any object (or class) in Ruby to list its methods, is there any function in Elixir to list all functions belonging to a module?  Something (at least remotely) like `String.functions` (where `String` could be replaced by any other module name)?

In Elixir, is there any way to get a module to list its functions?

I&#39;ve just started using Elixir, and have started a Phoenix project, which I enjoy a lot.
Now by having rails background, I&#39;m used to being spoiled with debugging tools like &quot;debugger&quot;, &quot;byebug&quot; and so on; I was wondering if there are any similar tools for Elixir? How are you guys debugging your Elixir applications?

Even an equivalent to Rubys `raise my_object.inspect`, would do wonders!

Thank you

Debugging and debugging tools in Elixir?

I&#39;m trying to print some debug information from one of my Controllers in my Phoenix app when the server is running.

&lt;!-- language: lang-ex --&gt;

    defmodule PhoenixApp.TopicController do
      use PhoenixApp.Web, :controller

      def index(conn, _params) do
        log(&quot;this text&quot;)

        # ... 
      end
    end

How to Log something in Controller when Phoenix Server is running?

In Python&#39;s nosetests you can just specify to run one test by calling its class followed by the test name. How can we do this with Elixir&#39;s ExUnit?

In Elixir&#39;s ExUnit, is it possible to just run one test?

I am reading [&quot;Elixir in Action&quot; book by Saša Jurić, and in the first chapter][1] it says:

&gt; Erlang processes are completely isolated from each other. They share
&gt; no memory, and a crash of one process doesn’t cause a crash of other
&gt; processes.

Isn&#39;t that true for Java threads as well?  I mean when Java thread crashes, it too does not crash other threads - especially, if we are looking at request-processing threads (lets exclude the `main` thread from this disucussion)


  [1]: https://manning-content.s3.amazonaws.com/download/b/b915834-e80b-4520-939d-ff1900057c15/elixir-in-action-CH01.pdf

Erlang Processes vs Java Threads

I&#39;m currently learning Elixir by going through the OTP and mix tutorial on the elixir-lang website, and I&#39;m having trouble finding out how to recompile and reload the project from within the shell.

In Erlang I would do `make:all([load])` and it would compile and load any changes that occurred.  However, in `iex` that always says `:up_to_date`, which does make sense, as Elixir uses mix for it&#39;s compiling needs.

I can&#39;t find any equivalent from within iex.

How do I recompile an Elixir project and reload it from within iex?

Functions defined by `defp` aren&#39;t exported so I can&#39;t execute them in places other than in the module.

Is there a way to test private functions in modules in ExUnit of Elixir?

When I do:

    IO.inspect [:right, :top, :left, ...very_long_list]

I only get the first items (it&#39;s a list of moves to solve a 15-puzzle) like this:

    [:right, :top, :left, :bot, :bot, :left, :top, :top, :right, :right, :bot,
      :left, :bot, :left, :top, :right, :bot, :right, :top, :top, :left, :bot,
      :left, :top, :right, :right, :bot, :bot, :left, :top, :top, :left, :bot,
      :right, :top, :right, :bot, :left, :left, :top, :right, :bot, :right, :top,
      :left, :left, :bot, ...] # =&gt; See the &#39;...&#39;
                                    instead, I would like 
                                    to get the complete list

How can I tell `IO.inspect` to not trim the list? Is there an option or something?

How to use IO.inspect on a long list without trimming it?

I can declare a range as follows:

    range = 1..10

Is there a way to convert the range to a list?

In Elixir, how can a range be converted to a list?

I&#39;m playing around with pattern match and I found out, that it&#39;s not quite easy to pattern match parameters of a method against an empty map. I thought it would go something like this:

    defmodule PatternMatch do
      def modify(%{}) do
        %{}
      end

      def modify(map) do
        # expensive operation
        %{ modified: &quot;map&quot; }
      end
    end

But it seems like the first function clause matches arbitrary maps:

    iex&gt; PatternMatch.modify(%{a: &quot;map&quot;})
    ==&gt; %{}

Is there another way to check for empty maps?

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