Clojure Interview Questions and Answers for 2 years experience

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Clojure Interview Questions and Answers

  1. What is Clojure?

    • Answer: Clojure is a dynamic, general-purpose programming language and a dialect of Lisp. It runs on the Java Virtual Machine (JVM), .NET, and JavaScript, emphasizing immutability, functional programming, and concurrency.

  2. Explain immutability in Clojure.

    • Answer: Immutability means that once a data structure is created, it cannot be changed. Instead of modifying existing data, operations create new data structures with the desired changes. This simplifies concurrency and reasoning about program behavior.

  3. What are the core data structures in Clojure?

    • Answer: The core data structures are lists (using `'()`), vectors (using `[]`), maps (using `{}`), and sets (using `#{}`). They are all immutable.

  4. How do you define a function in Clojure?

    • Answer: You define a function using `defn`. For example: `(defn my-function [arg1 arg2] (+ arg1 arg2))`

  5. Explain the difference between `let`, `letfn`, and `loop`?

    • Answer: `let` creates local bindings. `letfn` creates local functions. `loop` creates a local recursive function.

  6. What is a macro in Clojure?

    • Answer: A macro is a function that operates on code as data. It allows you to extend the language itself by creating new syntax or modifying existing syntax before it's evaluated.

  7. How do you handle exceptions in Clojure?

    • Answer: Using `try`, `catch`, and `finally`. The `try` block contains the code that might throw an exception, `catch` handles specific exceptions, and `finally` executes regardless of exceptions.

  8. Explain lazy sequences in Clojure.

    • Answer: Lazy sequences are sequences that are not evaluated until their values are actually needed. This can be very efficient for large datasets, as it avoids unnecessary computation.

  9. What is the purpose of the `map` function?

    • Answer: `map` applies a function to each element of a sequence and returns a new sequence containing the results.

  10. What is the purpose of the `filter` function?

    • Answer: `filter` selects elements from a sequence that satisfy a given predicate (a function that returns true or false).

  11. What is the purpose of the `reduce` function?

    • Answer: `reduce` applies a function cumulatively to the items of a sequence, reducing it to a single value.

  12. Explain the concept of atoms in Clojure.

    • Answer: Atoms are mutable references that provide thread-safe ways to manage mutable state within a predominantly immutable system. Changes to an atom are atomic operations.

  13. What are refs in Clojure? How do they differ from atoms?

    • Answer: Refs are also mutable references, but they are designed for more complex concurrent scenarios. Changes to a ref are transactional; either all changes succeed or none do, ensuring data consistency. Atoms are simpler and more suitable for less demanding concurrency situations.

  14. What are agents in Clojure?

    • Answer: Agents provide a mechanism for asynchronous updates to mutable state. Changes are queued and applied asynchronously, improving performance and responsiveness.

  15. Explain namespaces in Clojure.

    • Answer: Namespaces provide a way to organize code and avoid naming conflicts. They act as containers for functions, macros, and variables.

  16. What are some common Clojure libraries you've used?

    • Answer: (This will vary based on experience, but examples include: `core.async` for concurrency, `clojure.spec` for specification and validation, `ring` for web development, `compojure` for web routing, `datascript` or other database libraries.)

  17. How do you handle errors and logging in a Clojure application?

    • Answer: Using `try`/`catch`/`finally` for exception handling and libraries like `clojure.tools.logging` or `log4j` for structured logging.

  18. Describe your experience with Clojure's REPL (Read-Eval-Print Loop).

    • Answer: (Describe how you use it for testing, debugging, and interactive development. Mention tools like CIDER).

  19. How do you approach designing a Clojure application?

    • Answer: (Discuss approaches like functional decomposition, data-driven design, and emphasis on immutability and concurrency considerations. Mention any design patterns used.)

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