Racket Interview Questions and Answers for 10 years experience

1. What are the core principles of functional programming, and how are they implemented in Racket?

   • Answer: Core principles include immutability (data structures don't change after creation), first-class functions (functions treated as data), and pure functions (output depends only on input). Racket implements these through its immutable data structures (lists, vectors, etc.), its support for higher-order functions (functions that take other functions as arguments or return them), and its emphasis on referential transparency (expressions can be replaced with their values without changing program behavior).

2. Explain the difference between `let`, `let*`, and `letrec` in Racket. Provide examples.

   • Answer: `let` binds variables simultaneously. `let*` binds variables sequentially, allowing later bindings to depend on earlier ones. `letrec` allows recursive bindings, where a variable can be defined in terms of itself.
     Example:
     `(let ([x 1] [y (+ x 1)]) (+ x y))` ; x and y are bound simultaneously.
     `(let* ([x 1] [y (+ x 1)]) (+ x y))` ; Same result.
     `(letrec ([f (lambda (x) (if (= x 0) 1 (* x (f (- x 1))))]) (f 5))` ; Recursive factorial.

3. Describe the concept of macros in Racket and provide an example demonstrating their use.

   • Answer: Macros are code transformers. They operate on the code itself before it's evaluated, allowing you to extend Racket's syntax. This is powerful for creating DSLs (Domain-Specific Languages) or improving code readability.
     Example: A macro to define a simple loop:
     `(define-syntax-rule (my-loop init cond step body) (let loop ([i init]) (if cond body (loop step))))`
     Use: `(my-loop 0 (< i 10) (+ i 1) (printf "~a\n" i))`

4. How does Racket's module system work? Discuss its benefits and how it impacts code organization and reusability.

   • Answer: Racket's module system allows for the organization of code into separate units, promoting modularity and namespace management. Modules provide encapsulation, preventing naming conflicts and facilitating code reuse. They use `require` to import other modules and `provide` to export definitions. This leads to better maintainability and scalability in larger projects.

5. Explain the differences and use cases for lists, vectors, and hash tables in Racket.

   • Answer: Lists are linked lists, good for sequential processing but slower for random access. Vectors are arrays, efficient for random access but less efficient for insertions/deletions. Hash tables (using `hash`) provide fast key-value lookups, ideal for dictionaries or symbol tables.

6. What are continuations in Racket, and how can they be used to implement non-local control flow?

   • Answer: Continuations represent the rest of the computation. `call/cc` (call-with-current-continuation) captures the current continuation, allowing you to jump back to that point later, effectively altering the normal flow of execution. This enables features like exceptions, coroutines, and backtracking.

7. How would you handle exceptions and errors in a Racket program? Give examples of different error handling techniques.

   • Answer: Racket uses `with-handlers` to catch specific exceptions. You can define handlers for various error types (e.g., `exn:fail`, `exn:fail:contract`, etc.). `guard` can be used for more fine-grained control. Proper error handling includes clear error messages and graceful recovery mechanisms.

8. Discuss the concept of contracts in Racket and their role in ensuring code correctness.

   • Answer: Contracts specify pre- and post-conditions for functions, ensuring that they are used correctly. They help prevent runtime errors by checking the types and values of arguments and return values. Violations raise contract exceptions, aiding in debugging.

9. Explain how to work with files and I/O operations in Racket.

   • Answer: Racket provides functions like `open-input-file`, `open-output-file`, `read`, `read-line`, `write`, etc., for file I/O. Error handling (using `with-handlers`) is crucial when dealing with files. Remember to close files using `close-input-port` and `close-output-port` to avoid resource leaks.

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