Hiring guide for OCaml Engineers

OCaml Developer Hiring Guide

OCaml, short for Objective Caml, is a general-purpose programming language that supports functional, imperative and object-oriented styles of programming. It was developed in the mid-1990s by INRIA (French Institute for Research in Computer Science and Automation). OCaml features static type checking which helps catch errors at compile time rather than runtime. It also includes automatic memory management to prevent common issues like memory leaks or segmentation faults. The language is known for its expressiveness and efficiency; it allows developers to write high-level abstractions while maintaining performance close to languages like C++. OCaml has been used extensively in academia as well as industry sectors such as finance, tech companies etc., due to its reliability and robustness.

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

First 20 minutes

General OCaml app knowledge and experience

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

What are the main features of OCaml?
OCaml is a functional, imperative, and object-oriented programming language. It supports static typing, automatic memory management, first-class functions, and polymorphic functions. It also has a powerful module system and supports concurrent programming with threads.
How would you define a function in OCaml?
In OCaml, a function is defined using the 'let' keyword. For example, 'let add x y = x + y' defines a function named 'add' that takes two arguments and returns their sum.
What are variants in OCaml?
Variants in OCaml are a way to define a type by enumerating its possible values. They are similar to enums in C, but can also carry additional data. For example, 'type shape = Circle of float | Rectangle of float * float' defines a type 'shape' that can be either a 'Circle' with a single float (representing the radius), or a 'Rectangle' with two floats (representing the width and height).
How would you handle exceptions in OCaml?
Exceptions in OCaml can be handled using the 'try' and 'with' keywords. For example, 'try some_function () with Failure msg -> print_endline msg' would catch the exception 'Failure' and print its message.
What is the difference between 'let' and 'let rec' in OCaml?
'let' is used to define a variable or a function, while 'let rec' is used to define a recursive function. Without the 'rec' keyword, the function wouldn't be able to call itself.
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What you’re looking for early on

Does the candidate have a solid understanding of OCaml's functional programming principles?
Can the candidate demonstrate an ability to solve complex problems using OCaml?
Has the candidate worked on projects or tasks that required them to use OCaml extensively?
Does the candidate show an understanding of OCaml's type system?

Next 20 minutes

Specific OCaml 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.

What are polymorphic functions in OCaml?
Polymorphic functions in OCaml are functions that can operate on values of different types. For example, the function 'let id x = x' is polymorphic because it can take a value of any type and return a value of the same type.
How would you implement a map function in OCaml?
A map function can be implemented in OCaml using recursion. For example, 'let rec map f xs = match xs with [] -> [] | x::xs' -> f x :: map f xs' defines a map function that applies a function 'f' to each element of a list 'xs'.
What is the difference between '::' and '@' in OCaml?
'::' is used to add an element to the front of a list, while '@' is used to concatenate two lists. For example, '1 :: [2; 3]' results in '[1; 2; 3]', while '[1; 2] @ [3; 4]' results in '[1; 2; 3; 4]'.
What are functors in OCaml?
Functors in OCaml are modules that are parameterized by other modules. They can be thought of as functions at the module level.
How would you implement a binary search tree in OCaml?
A binary search tree can be implemented in OCaml using a variant type for the nodes and recursive functions for the operations. For example, 'type 'a bst = Empty | Node of 'a * 'a bst * 'a bst' defines a binary search tree with 'Empty' nodes and 'Node' nodes that contain a value and two subtrees.
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The ideal back-end app developer

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

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

What does the following OCaml code do?
let rec factorial n = if n = 0 then 1 else n * factorial (n - 1)
This code defines a recursive function to calculate the factorial of a number. If the input number is 0, it returns 1. Otherwise, it multiplies the number by the factorial of the number minus one.
What will be the output of the following OCaml code?
let x = 5 in let y = 10 in x + y
The output of this code will be 15. It first assigns 5 to x, then assigns 10 to y, and finally adds x and y together.
What does the following OCaml code do?
let rec map f = function | [] -> [] | h::t -> f h :: map f t
This code defines a recursive function that applies a function to each element of a list. If the list is empty, it returns an empty list. Otherwise, it applies the function to the head of the list and concatenates the result with the mapped tail of the list.
What does the following OCaml code do?
let spawn f x = let _ = Thread.create f x in ()
This code defines a function that creates a new thread to execute a function with a given argument. The function does not return any value.

Wrap-up questions

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

What is the difference between '=' and '==' in OCaml?
'=' is used for structural equality, meaning that two values are equal if they have the same structure. '==' is used for physical equality, meaning that two values are equal if they are the exact same object in memory.
What are first-class functions in OCaml?
First-class functions in OCaml are functions that can be treated as values. They can be assigned to variables, passed as arguments to other functions, and returned as results from other functions.
How would you implement memoization in OCaml?
Memoization can be implemented in OCaml by using a hashtable to store the results of function calls. Before computing the result of a function, you would check if the result is already in the hashtable. If it is, you would return the stored result. If it's not, you would compute the result, store it in the hashtable, and then return it.

OCaml application related

Product Perfect's OCaml development capabilities

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