20 Clojure Interview Questions and Answers

Clojure is a powerful programming language that is gaining popularity in the software development community. If you are interviewing for a position that requires Clojure skills, it is important to be prepared to answer questions about your experience and knowledge. In this article, we review some of the most common Clojure interview questions and provide tips on how to answer them.

Clojure Interview Questions and Answers

Here are 20 commonly asked Clojure interview questions and answers to prepare you for your interview:

1. What is Clojure?

Clojure is a dialect of the Lisp programming language. It is a general-purpose programming language that features a strong dynamic type system and powerful macro system. Clojure is also notable for its focus on immutability and concurrency, which makes it a great choice for developing scalable, concurrent applications.

2. Is it possible to run Clojure on the JVM without using Java code? If yes, then how do you go about doing that?

Yes, it is possible to run Clojure on the JVM without using Java code. You can do this by using the Clojure compiler to compile your Clojure code into JVM bytecode, which can then be run on the JVM.

3. Can you explain what immutable data structures are and why they’re used in Clojure?

Immutable data structures are data structures that cannot be changed after they have been created. This is in contrast to mutable data structures, which can be changed after they have been created. Immutable data structures are used in Clojure because they are more efficient and easier to reason about than mutable data structures.

4. Can you explain how to use a recursive function in Clojure?

A recursive function is a function that calls itself. In Clojure, you can create a recursive function by using the recur keyword. For example, the following function will return the factorial of a number:

(defn factorial [n]
(if (= n 1)
1
(* n (recur (dec n)))))

5. How would you define a macro in Clojure?

A macro in Clojure is a piece of code that takes another piece of code as input and outputs a transformed piece of code. Macros are used to extend the functionality of the Clojure language itself.

6. What’s the difference between a lazy sequence and an eager sequence? Which one should I prefer in certain situations?

A lazy sequence is one that is not evaluated until it is needed, while an eager sequence is one that is evaluated as soon as it is created. Lazy sequences can be more efficient in some situations because they are not evaluated until they are needed, but they can also be more difficult to work with because they can be harder to debug.

7. What is your opinion on tail-recursive functions?

I believe that tail-recursive functions can be very useful in some situations, but they are not always the best solution. In general, I think that tail-recursive functions can be a good way to improve performance and avoid stack overflows, but they can also make code more difficult to read and debug.

8. Can you explain how to create a named function in Clojure?

In Clojure, you can create a named function using the defn keyword. For example, the following code defines a function named add that takes two arguments and returns their sum:

(defn add [a b]
(+ a b))

9. What’s the difference between defn and defmacro?

The main difference between defn and defmacro is that defn defines a function, while defmacro defines a macro. A macro is a piece of code that is executed at compile time, while a function is executed at runtime. This means that macros have more power than functions, but they can also be more difficult to debug.

10. What is the purpose of meta-data in Clojure? When would I need to use them?

Meta-data in Clojure is used to annotate data. This can be useful for a number of reasons, such as providing information about the data that can be used by programs, or for documentation purposes. Meta-data can be attached to any data type in Clojure, including symbols, numbers, strings, and collections.

11. What is STM? Why is it useful when programming with Clojure?

STM is short for software transactional memory. It is a system that allows Clojure programmers to manage concurrent changes to shared data structures in a safe and consistent way. STM is useful because it helps to avoid the need for locks, which can lead to deadlocks.

12. What’s the difference between let and binding?

Let is a special form that creates a new local binding. Binding creates a new thread-local binding.

13. What is multimethods? How is it different from polymorphism?

Multimethods are a form of polymorphism that allows for different behavior based on not just the type of an object, but also on the value of that object. This is different from traditional polymorphism, which only allows for different behavior based on the type of an object.

14. What does ‘@’ mean in Clojure?

The ‘@’ symbol in Clojure is used to denote a dereferencing of a reference. So, if you have a reference to a value stored in a variable, using the ‘@’ symbol will allow you to access the actual value stored in the variable.

15. What is transducers? How do you think it will affect future versions of Clojure?

Transducers is a new feature in Clojure that allows for the composition of data transformation functions. This is a powerful tool that can be used to create concise and efficient code. I think it will have a big impact on future versions of Clojure, as it will allow for more complex data transformations to be performed more easily.

16. What’s the difference between Symbol and Keyword?

A Symbol is a unique identifier that can be used to reference a value, while a Keyword is a type of Symbol that is used to identify a specific value. A Keyword can be thought of as a “label” that is attached to a value, while a Symbol can be thought of as a “name” that can be used to reference a value.

17. What is atoms? Why are they important for concurrent processing?

Atoms are one of the basic data types in Clojure, and they are important for concurrent processing because they are immutable. This means that they can be safely shared between different threads without the risk of data corruption.

18. What are agents? When and where would you use them?

Agents are a type of concurrent data structure in Clojure that are used to manage state. They are used to asynchronously send and receive messages in order to update their state. You would use agents when you need to have a concurrent data structure that can be updated asynchronously.

19. What functionality does reduce provide?

The reduce function is used to apply a function to a sequence of items, in order to reduce the sequence to a single value. This is often used as a way to combine a sequence of items into a single value, such as when summing a list of numbers.

20. What is the main advantage of Clojure over other languages like Scala or Haskell?

The main advantage of Clojure is that it is a Lisp dialect, which means that it has a very powerful macro system. This allows for a great deal of flexibility and customizability that is not possible with other languages.