Ask the right questions to secure the right Elixir talent among an increasingly shrinking pool of talent.

Elixir is a dynamic, functional programming language designed for building scalable and maintainable applications. It was created by José Valim in 2011 to enable higher extensibility and productivity in the Erlang VM while maintaining compatibility with Erlang's ecosystem. Elixir leverages the Erlang BEAM (Bogdan's Erlang Abstract Machine) to build distributed, fault-tolerant applications with real-time guarantees and hot code upgrades. The language provides metaprogramming capabilities through macros, polymorphism via protocols, and support for concurrency. Elixir has been adopted by companies like Pinterest and Moz for its robustness, performance, and scalability.

First 20 minutes

General Elixir knowledge and experience

The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.

How would you define a module in Elixir?

In Elixir, you define a module using the 'defmodule' keyword followed by the module name and do/end block. Inside the block, you can define functions using 'def' keyword.

What is Mix in Elixir?

Mix is a build tool that provides tasks for creating, compiling, and testing Elixir projects, managing its dependencies, and more.

How would you install Elixir in your local machine?

You can install Elixir using various package managers depending on your operating system. For example, on macOS, you can use Homebrew and run 'brew install elixir'.

What are the key features of Elixir?

Some key features of Elixir include its scalability, fault tolerance, functional programming, extensibility, and compatibility with the Erlang ecosystem.

How would you define Elixir?

Elixir is a dynamic, functional language designed for building scalable and maintainable applications. It leverages the Erlang VM, known for running low-latency, distributed, and fault-tolerant systems.

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What youre looking for early-on

Does the candidate have experience with Elixir-based frameworks like Phoenix?

Phoenix is a popular web framework in the Elixir ecosystem. Experience with it or similar frameworks shows that the candidate can build web applications using Elixir.

Can the candidate demonstrate a good understanding of concurrent programming in Elixir?

Elixir is known for its concurrency model. A good Elixir developer should be able to write code that can run concurrently without issues.

Does the candidate have experience with Elixir's testing tools like ExUnit?

Testing is a critical part of software development. The candidate should be familiar with Elixir's testing tools to ensure the quality of their code.

Is the candidate able to solve problems effectively and efficiently using Elixir?

This will show that the candidate can use Elixir to its full potential and can handle the tasks that will be assigned to them.

Can the candidate demonstrate experience with OTP (Open Telecom Platform)?

OTP is a set of Elixir libraries and principles providing tools to build scalable and maintainable applications. It's crucial for an Elixir developer to have experience with it.

Does the candidate have a solid understanding of Elixir's syntax and semantics?

This is fundamental to any programming role. The candidate should be able to write and understand Elixir code with ease.

Next 20 minutes

Specific Elixir development questions

The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.

How would you implement concurrency in Elixir?

Elixir provides first-class support for concurrency. You can create lightweight processes using 'spawn' function, send messages to them using 'send' function, and receive messages using 'receive' construct.

What is pattern matching in Elixir?

Pattern matching is a powerful feature in Elixir that allows you to match simple as well as complex data structures, destructure data, and control program flow.

Describe the difference between '==' and '===' in Elixir.

'==' operator compares the values and returns true if they are equal. '===' operator, on the other hand, is more strict and also considers the data type of the values.

How would you handle errors in Elixir?

Elixir uses a mechanism called 'exceptions' to handle errors. You can raise an exception using 'raise' function and handle it using 'try/rescue' construct.

What are the data types supported by Elixir?

Elixir supports several data types such as integers, floats, booleans, atoms, strings, lists, tuples, maps, and binary.

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A skilled Elixir engineer should demonstrate proficiency in functional programming, deep understanding of the Elixir language and ecosystem, and experience with OTP for building scalable applications. Red flags include lack of knowledge about concurrent processes or inability to solve complex problems using Elixir.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with Elixir.

What does the following Elixir code do?IO.puts "Hello, World!"
This code prints the string 'Hello, World!' to the console.
What will be the output of the following Elixir code?IO.inspect(Enum.map([1, 2, 3, 4], fn x -> x * 2 end))
This code will output a list of numbers [2, 4, 6, 8]. It uses the Enum.map function to iterate over the list [1, 2, 3, 4] and multiplies each element by 2.
What does the following Elixir code do?Enum.reduce([1, 2, 3], 0, fn(x, acc) -> x + acc end)
This code sums up the elements in the list [1, 2, 3]. It uses the Enum.reduce function, which takes an enumerable, an accumulator (initial value), and a function. The function is applied to each element in the enumerable, and the result is accumulated.
What does the following Elixir code do?Task.async(fn -> 1 + 2 end) |> Task.await
This code executes the function (1 + 2) asynchronously in a separate process and waits for the result. It uses the Task.async function to start an asynchronous task and Task.await to get the result of the task.
What does the following Elixir code do?defmodule Math do
def add(a, b), do: a + b
end
This code defines a module named Math with a function add. The add function takes two parameters and returns their sum.
What will be the output of the following Elixir code?defmodule Test do
  defmacro __using__(_) do
    quote do
      def test do
        IO.puts "Test"
      end
    end
  end
end
defmodule Example do
  use Test
end
Example.test
This code will output the string 'Test'. It defines a macro __using__ in the Test module, which when used in another module (Example in this case), injects the defined function (test) into that module.

Wrap-up questions

Final candidate for Elixir role questions

The final few interview questions for a Elixir candidate should typically focus on a combination of technical skills, personal goals, growth potential, team dynamics, and company culture.

How would you deploy an Elixir application?

You can deploy an Elixir application using various tools and techniques. One common approach is to use Distillery to create a release, and then use Docker to containerize and deploy the application.

What is the role of 'Supervisor' in Elixir?

A Supervisor in Elixir is a process which supervises other processes, known as its children. Supervisors are used to build a hierarchical process structure called 'supervision tree', which is used to build fault-tolerant systems.

How would you create a GenServer in Elixir?

You can create a GenServer by defining a module and using 'GenServer' behaviour. The module needs to implement two callback functions: 'init/1' and 'handle_call/3'.

Describe the difference between 'list' and 'tuple' in Elixir.

Lists are stored in memory as linked lists, making it efficient to insert elements at the head. Tuples, on the other hand, are stored contiguously in memory, making it efficient to access an element by index.

What is OTP in the context of Elixir?

OTP (Open Telecom Platform) is a set of libraries and design principles in Erlang that Elixir leverages to build robust, fault-tolerant, distributed applications.

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Elixir application related

Product Perfect's Elixir development capabilities

Beyond hiring for your Elixir engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in Elixir projects, and can engage in multiple capacities.

Elixir Consultive assessments

Elixir Application Conversion Assessment Elixir Application Integration Assessment Elixir Data & Database Integration Assessment

Custom Elixir development projects

Custom Elixir App Conversion Elixir Custom App Development Process App UI Design for Elixir Facelifts

Elixir Developer Hiring Guide

Hiring Guide for Elixir Engineers

First 20 minutes

General Elixir knowledge and experience

How would you define a module in Elixir?

What is Mix in Elixir?

How would you install Elixir in your local machine?

What are the key features of Elixir?

How would you define Elixir?

What youre looking for early-on

Does the candidate have experience with Elixir-based frameworks like Phoenix?

Can the candidate demonstrate a good understanding of concurrent programming in Elixir?

Does the candidate have experience with Elixir's testing tools like ExUnit?

Is the candidate able to solve problems effectively and efficiently using Elixir?

Can the candidate demonstrate experience with OTP (Open Telecom Platform)?

Does the candidate have a solid understanding of Elixir's syntax and semantics?

Next 20 minutes

Specific Elixir development questions

How would you implement concurrency in Elixir?

What is pattern matching in Elixir?

Describe the difference between '==' and '===' in Elixir.

How would you handle errors in Elixir?

What are the data types supported by Elixir?

The ideal back-end app developer

What you’re looking to see on the Elixir engineer at this point.

What does the following Elixir code do?

This code prints the string 'Hello, World!' to the console.

What will be the output of the following Elixir code?

This code will output a list of numbers [2, 4, 6, 8]. It uses the Enum.map function to iterate over the list [1, 2, 3, 4] and multiplies each element by 2.

What does the following Elixir code do?

This code sums up the elements in the list [1, 2, 3]. It uses the Enum.reduce function, which takes an enumerable, an accumulator (initial value), and a function. The function is applied to each element in the enumerable, and the result is accumulated.

What does the following Elixir code do?

This code executes the function (1 + 2) asynchronously in a separate process and waits for the result. It uses the Task.async function to start an asynchronous task and Task.await to get the result of the task.

What does the following Elixir code do?

This code defines a module named Math with a function add. The add function takes two parameters and returns their sum.

What will be the output of the following Elixir code?

This code will output the string 'Test'. It defines a macro __using__ in the Test module, which when used in another module (Example in this case), injects the defined function (test) into that module.

Wrap-up questions

Final candidate for Elixir role questions

How would you deploy an Elixir application?

What is the role of 'Supervisor' in Elixir?

How would you create a GenServer in Elixir?

Describe the difference between 'list' and 'tuple' in Elixir.

What is OTP in the context of Elixir?

Elixir Consultive assessments

Custom Elixir development projects

This code will output the string 'Test'. It defines a macro using in the Test module, which when used in another module (Example in this case), injects the defined function (test) into that module.