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Clojure is a dynamic, general-purpose programming language, combining the approachability and interactive development of a scripting language with an efficient and robust infrastructure for multithreaded programming. It was created by Rich Hickey and first released in 2007, with its development funded by the company Cognitect. Clojure is a dialect of the Lisp programming language and runs on the Java Virtual Machine, JavaScript engines, and Common Language Runtime. It emphasizes functional programming, offering immutable data structures and encouraging developers to write pure functions. The language's design allows it to handle concurrent processing, making it a popular choice for multi-core processing tasks.

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

First 20 minutes

General Clojure app knowledge and experience

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

How would you define a function in Clojure?

You can define a function in Clojure using the 'defn' keyword. For example: (defn add [a b] (+ a b)). This defines a function named 'add' that takes two parameters, a and b, and returns their sum.

What are the core data structures in Clojure?

The core data structures in Clojure are lists, vectors, maps, and sets.

Describe the difference between a vector and a list in Clojure.

In Clojure, vectors and lists are both sequences, but they have different performance characteristics. Vectors have constant-time access and update for elements at any position, while lists have constant-time access and update only for the first element.

How would you handle exceptions in Clojure?

In Clojure, exceptions can be handled using the 'try'/'catch'/'finally' construct, similar to Java. The 'try' block contains the code that might throw an exception, the 'catch' block contains the code to handle the exception, and the 'finally' block contains the code that will be executed regardless of whether an exception was thrown or not.

What are Clojure macros?

Macros in Clojure are a way to define reusable chunks of code. They are functions that are executed at compile time and can generate and include code in the program.

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What you’re looking for early on

Does the candidate have a solid understanding of functional programming concepts?

Has the candidate demonstrated the ability to work with Clojure's syntax and data structures?

Can the candidate effectively use Clojure's concurrency and parallelism features?

Is the candidate comfortable with Clojure's macro system?

Next 20 minutes

Specific Clojure 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 'let' and 'def' in Clojure.

'def' is used to define a global variable, while 'let' is used to define local variables. Variables defined with 'let' are only accessible within the 'let' block, while variables defined with 'def' are accessible throughout the program.

How would you implement a loop in Clojure?

In Clojure, you can implement a loop using the 'loop'/'recur' construct. The 'loop' expression initializes the loop variables, and the 'recur' expression updates the loop variables and jumps back to the 'loop' expression.

What are multimethods in Clojure?

Multimethods in Clojure provide a way to define a function that can have different implementations depending on the type or value of its arguments. This is done using the 'defmulti' and 'defmethod' forms.

Describe the difference between 'apply' and 'map' in Clojure.

'apply' takes a function and a sequence of arguments, and calls the function with those arguments. 'map' takes a function and one or more sequences, and applies the function to each element of the sequences, returning a sequence of results.

How would you handle concurrency in Clojure?

Clojure provides several constructs for handling concurrency, including atoms, agents, refs, and vars. These constructs provide a way to manage mutable state in a safe and consistent way in a concurrent program.

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At this point, a skilled Clojure engineer should demonstrate strong problem-solving abilities, proficiency in Clojure 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 Clojure.

What does the following Clojure code do?
(defn hello-world [] (println "Hello, World!"))
This code defines a function named 'hello-world' that prints the string 'Hello, World!' when called.
What will be the output of the following Clojure code?
(defn add-numbers [a b] (+ a b)) (add-numbers 5 10)
This code will output 15. It defines a function 'add-numbers' that takes two arguments and returns their sum. It then calls this function with the arguments 5 and 10.
What does the following Clojure code do?
(defn filter-even [coll] (filter even? coll))
This code defines a function 'filter-even' that takes a collection and returns a new collection with only the even numbers. It uses the built-in 'filter' function and the 'even?' predicate.
What does the following Clojure code do?
(defn run-in-thread [f] (Thread. f))
This code defines a function 'run-in-thread' that takes a function 'f' and runs it in a new thread. It uses the 'Thread.' constructor to create a new thread.

Wrap-up questions

Final candidate for Clojure 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 Clojure application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

What are transducers in Clojure?

Transducers in Clojure are a way to define and compose transformations on data. A transducer is a function that takes a reducing function as an argument and returns a new reducing function that incorporates the transformation.

Describe the difference between 'reduce' and 'fold' in Clojure.

'reduce' takes a function and a sequence, and applies the function to the elements of the sequence in a pairwise way, accumulating a single result. 'fold' is similar, but it can split the sequence into chunks and process them in parallel, which can be more efficient for large sequences.

How would you implement memoization in Clojure?

In Clojure, you can implement memoization using the 'memoize' function. This function takes a function as an argument and returns a new function that caches the results of the original function for each set of arguments.

Clojure application related

Product Perfect's Clojure development capabilities

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

Clojure Consultive assessments

Clojure Application Conversion Assessment Clojure Application Integration Assessment Clojure Data & Database Integration Assessment

Custom Clojure development projects

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

Hiring guide for Clojure Engineers

Clojure Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

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

Clojure Consultive assessments

Custom Clojure development projects