Hiring guide for Elm Engineers

Elm Developer Hiring Guide

Elm is a functional programming language for front-end web development, designed to foster robust, complex applications. Introduced by Evan Czaplicki in 2012 as part of his thesis at Harvard University, Elm was created with the goal of improving GUI architecture. The language is known for its strong type inference and friendly error messages that make it beginner-friendly. Elm compiles to JavaScript, making it compatible with all major browsers. It has gained popularity due to its performance benefits and emphasis on developer productivity and code reliability.

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

First 20 minutes

General Elm app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in Elm application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

How would you install Elm?
You can install Elm using npm with the command 'npm install -g elm'.
What are some benefits of using Elm?
Some benefits of using Elm include strong static typing, no runtime exceptions, great performance, and easy refactoring.
How would you declare a variable in Elm?
In Elm, you can declare a variable using the 'let' keyword, like 'let x = 5'.
What is the Elm Architecture?
The Elm Architecture is a pattern for architecting interactive programs, like webapps and games. It has three parts: Model, Update, and View.
How would you create a function in Elm?
In Elm, you can create a function using the following syntax: 'functionName parameter = expression'.
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What you’re looking for early on

Does the candidate have a solid understanding of Elm's architecture?
Has the candidate demonstrated the ability to write clean, efficient Elm code?
Is the candidate familiar with Elm's type system?
Can the candidate effectively debug Elm applications?

Next 20 minutes

Specific Elm development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

Describe the difference between a record and a tuple in Elm.
A record is a collection of key-value pairs, while a tuple is an ordered collection of values. Records have named fields and are used when you need to bundle related data together. Tuples are used when you need to group a fixed number of values together for a specific purpose.
What are Elm signals?
Elm signals are values that change over time. They are used to handle events and user input in an Elm application.
How would you handle errors in Elm?
Elm uses a type called 'Result' for error handling. The 'Result' type can be 'Ok' or 'Err', and you can pattern match on it to handle different cases.
What is the purpose of the 'Maybe' type in Elm?
The 'Maybe' type is used to handle optional values and null checks. It can be 'Just value' or 'Nothing'.
Describe the difference between 'map' and 'andThen' in Elm.
'map' is used to apply a function to a value inside a context, like 'Maybe' or 'Result'. 'andThen' is used to chain operations that might fail, it takes a function that returns a context and a value inside a context.
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The ideal back-end app developer

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

At this point, a skilled Elm engineer should demonstrate strong problem-solving abilities, proficiency in Elm programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

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

What does the following Elm code do?
import Html exposing (text)
main = text "Hello, World!"
This Elm code displays the text 'Hello, World!' on the web page.
What will be the output of the following Elm code?
import Html exposing (..)
main = div [] [ text "Hello", text "World" ]
This Elm code will output a div element with two text nodes 'Hello' and 'World'.
What does the following Elm code do?
import List exposing (map)
main = map ((*) 2) [1, 2, 3, 4, 5]
This Elm code multiplies each element in the list [1, 2, 3, 4, 5] by 2.
What does the following Elm code do?
import Task
import Time exposing (second)
main = Task.sleep (2 * second)
This Elm code creates a task that sleeps for 2 seconds.

Wrap-up questions

Final candidate for Elm Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle Elm application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

How would you send a HTTP request in Elm?
You can send a HTTP request in Elm using the 'Http' module. You need to create a 'Request' and send it using 'Http.send'.
What are Elm subscriptions?
Elm subscriptions are a way to listen to external events, like websockets and time. They are used in the Elm Architecture to handle events that don't originate from user input.
How would you handle side effects in Elm?
Side effects in Elm are handled using commands. A command is a value that represents a side effect, like a HTTP request or a random number generation.

Elm application related

Product Perfect's Elm development capabilities

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