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The clean computer programming language, developed in the late 1980s by a team at Radboud University in the Netherlands, is a functional language known for its purity and strong typing. Known for its ability to eliminate side effects, it was originally designed as a tool for teaching and research. Its unique feature is the use of graph rewriting as an implementation method, which allows for efficient memory usage. The language also supports generic programming and higher-order functions. This information is sourced from the official Clean Language website and various academic papers on computer science.

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

First 20 minutes

General Clean app knowledge and experience

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

What is the main purpose of Clean programming language?

The main purpose of Clean programming language is to facilitate the development of software systems that are highly reliable, efficient and easy to maintain.

How would you explain the concept of 'uniqueness typing' in Clean?

Uniqueness typing in Clean is a type system feature that ensures that certain data objects have a single reference to them at any given time. This allows for efficient in-place updates of data structures.

What are the key features of Clean programming language?

Key features of Clean include its purely functional nature, its strong static type system, its support for concurrent and distributed computing, and its unique approach to managing state through uniqueness typing.

Describe the difference between Clean and Haskell.

While both Clean and Haskell are purely functional programming languages, there are several differences. Clean uses uniqueness typing to manage state and perform in-place updates of data structures, while Haskell uses monads. Additionally, Clean has built-in support for graph rewriting, which is not present in Haskell.

How would you handle state in Clean?

In Clean, state is handled through the use of uniqueness typing. This allows for efficient in-place updates of data structures, while still maintaining the benefits of pure functional programming.

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What you’re looking for early on

Has the candidate demonstrated a strong understanding of Clean language and its syntax?

Does the candidate show good problem-solving skills?

Is the candidate able to communicate effectively about technical concepts?

Has the candidate shown any experience with testing and debugging in Clean?

Next 20 minutes

Specific Clean 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 the advantages of using Clean over other functional programming languages?

Advantages of using Clean include its efficient runtime performance, its unique approach to managing state through uniqueness typing, and its support for concurrent and distributed computing.

How would you implement concurrency in Clean?

Concurrency in Clean can be implemented using the Concurrent Clean language extension, which provides primitives for creating and managing concurrent threads.

Describe the difference between strict and lazy evaluation in Clean.

Strict evaluation means that expressions are evaluated as soon as they are bound to a variable, while lazy evaluation means that expressions are not evaluated until their results are actually needed. Clean supports both strict and lazy evaluation.

How would you handle exceptions in Clean?

Clean provides a mechanism for exception handling through the use of the 'Exception' type and the 'catch' function. Exceptions can be thrown using the 'raise' function.

What are the disadvantages of using Clean?

Disadvantages of using Clean include its relatively small user community and the lack of libraries and tools compared to other languages like Haskell.

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

What does the following code do?
public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"); } }
This code prints 'Hello, World!' to the console.
What will be the output of the following code?
public class Test { public static void main(String[] args) { int x = 10; int y = 20; x += y; System.out.println(x); } }
The output of the code will be 30. It adds the value of y (which is 20) to the value of x (which is 10) and assigns the result to x.
What does the following code do?
import java.util.Arrays; public class Test { public static void main(String[] args) { int[] array = {1, 2, 3, 4, 5}; Arrays.sort(array); System.out.println(Arrays.toString(array)); } }
This code sorts the array in ascending order and then prints the sorted array to the console.
What does the following code do?
public class Test { public static void main(String[] args) { Thread thread = new Thread(() -> { System.out.println("New thread created."); }); thread.start(); } }
This code creates a new thread and runs a task in that thread which prints 'New thread created.' to the console.

Wrap-up questions

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

How would you optimize a Clean program for performance?

Performance optimization in Clean can involve a variety of techniques, including careful management of state through uniqueness typing, efficient use of data structures, and judicious use of strict evaluation.

Describe the difference between Clean and imperative programming languages.

The main difference between Clean and imperative languages is that Clean is a purely functional language, meaning that functions in Clean have no side effects. In contrast, imperative languages allow functions to change the state of the program.

How would you implement a complex algorithm in Clean?

Implementing a complex algorithm in Clean would involve breaking the problem down into smaller, manageable functions, and then composing these functions together to solve the problem. The use of higher-order functions and data structures would likely be involved.

Clean application related

Product Perfect's Clean development capabilities

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

Clean Consultive assessments

Clean Application Conversion Assessment Clean Application Integration Assessment Clean Data & Database Integration Assessment

Custom Clean development projects

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

Hiring guide for Clean Engineers

Clean Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

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

Clean Consultive assessments

Custom Clean development projects