Hiring guide for Prolog Engineers

Prolog Developer Hiring Guide

Prolog is a high-level programming language based on formal logic. It was developed in the 1970s and is primarily used in artificial intelligence (AI) and computational linguistics. Prolog stands for "PROgramming in LOGic" and it's one of the first logic programming languages. Unlike many other programming languages, Prolog uses declarative semantics, meaning that programs are written as logical declarations rather than explicit instructions to be carried out by a machine. This makes it particularly suited for tasks involving complex data structures or where there are many possible solutions to a problem. Prolog allows programmers to describe relationships between entities (facts), rules about those relationships, and queries about those facts and rules. The language then automatically handles searching through the possible solutions or outcomes. It has built-in support for backtracking - an algorithmic technique of solving problems recursively by trying different solutions until finding one that works, which makes it ideal for search-based AI applications such as game playing, theorem proving, expert systems etc. Despite its power in certain areas like AI research and teaching purposes due to its unique approach towards problem-solving paradigm; Prolog's use isn't widespread across all domains because of its steep learning curve compared with more conventional procedural or object-oriented languages like Python or Java.

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

First 20 minutes

General Prolog app knowledge and experience

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

What are the basic data types in Prolog?
The basic data types in Prolog are atoms, numbers, variables and compound terms.
How would you define a fact in Prolog?
In Prolog, a fact is defined as a basic assertion about some world. It is expressed in the form of a predicate followed by terms, ending with a period. For example, 'loves(john, mary).'
What is a rule in Prolog?
A rule in Prolog is a statement that can be read as an implication. It consists of a head and a body, separated by ':-'. The head is a single atomic formula and the body is a conjunction of atomic formulas.
What is the purpose of the cut operator in Prolog?
The cut operator is used to control the execution of a Prolog program. It is used to prune the search tree and to prevent backtracking to certain points in the program.
How would you implement recursion in Prolog?
Recursion in Prolog is implemented by defining a rule that calls itself. The base case is defined as a fact and the recursive case is defined as a rule.
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What you’re looking for early on

Does the candidate have a strong understanding of Prolog's syntax and semantics?
How well does the candidate understand logical programming and its paradigms?
Can they demonstrate experience with real-world Prolog projects?
Are they able to solve complex problems using Prolog?

Next 20 minutes

Specific Prolog 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 different types of variables in Prolog?
There are three types of variables in Prolog: anonymous variables, singleton variables, and named variables.
How would you use lists in Prolog?
Lists in Prolog are used to represent sequences of items. They are defined using square brackets and items are separated by commas. For example, '[a, b, c]' is a list of three elements.
Describe the difference between a fact and a rule in Prolog.
A fact in Prolog is a basic assertion about something, while a rule is an implication that states that if certain conditions are met, then other conditions also hold true.
What is unification in Prolog?
Unification is the process of making two terms equal. It is the basic operation that allows Prolog to match patterns and to assign values to variables.
How would you use the fail predicate in Prolog?
The fail predicate in Prolog is used to force backtracking. When Prolog encounters the fail predicate, it backtracks to find other solutions.
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The ideal back-end app developer

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

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

What does this simple Prolog rule do: loves(romeo, juliet)?
loves(romeo, juliet).
This is a fact stating that Romeo loves Juliet in Prolog.
What will be the output of the following Prolog code if you query 'parent(X, Y)?': parent(tom, jim). parent(jim, ann).
parent(tom, jim).
parent(jim, ann).
The output will be a list of all parent-child relationships defined in the facts. In this case, it will return that Tom is a parent of Jim and Jim is a parent of Ann.
What does this Prolog code do: member(X, [X|_]). member(X, [_|T]) :- member(X, T).
member(X, [X|_]).
member(X, [_|T]) :- member(X, T).
This code defines a member predicate that checks if an element X is a member of a list. The first rule states that X is a member if it is the head of the list. The second rule states that X is a member if it is a member of the tail of the list.
In Prolog, how would you represent a thread that executes the goal 'write('Hello, World!')'?
thread_create(write('Hello, World!'), _, []).
This code creates a new thread that executes the goal 'write('Hello, World!')'.

Wrap-up questions

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

What are DCGs in Prolog and how would you use them?
DCGs or Definite Clause Grammars are a feature of Prolog that allows the definition of grammars in a natural and readable way. They are used for parsing and generating sequences.
How would you implement a breadth-first search algorithm in Prolog?
A breadth-first search algorithm in Prolog can be implemented by using a queue data structure. The algorithm starts by visiting the root node, then all its neighbors, and so on.
Describe the difference between green cuts and red cuts in Prolog.
Green cuts do not affect the logical meaning of a program, they only improve its efficiency. Red cuts, on the other hand, do affect the logical meaning of a program and can change its behavior.

Prolog application related

Product Perfect's Prolog development capabilities

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