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Ask the right questions to secure the right Lisp talent among an increasingly shrinking pool of talent.
Lisp, developed by John McCarthy in 1958 at MIT, is one of the oldest high-level programming languages still in widespread use today. It was originally created as a practical mathematical notation for computer programs and quickly became the favored language for artificial intelligence (AI) research. The language's fully parenthesized prefix notation allows it to process symbolic information effectively, making it particularly suitable for AI programming. Lisp has spawned many variant languages such as Scheme and Clojure and has significantly influenced Python, Ruby, and others with its distinctive features like code-as-data philosophy and powerful macro system. Its longevity testifies to its innovative design features that continue to inspire modern software development paradigms. Sources: 1) McCarthy J., "Recursive Functions of Symbolic Expressions," Communications of the ACM 3(4), April 1960. 2) Seibel P., "Coders at Work: Reflections on the Craft of Programming," Apress, Septembe
The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.
Recursion in Lisp can be implemented by calling the function within its own definition. For example, a recursive function to calculate factorial would be: (defun factorial (n) (if (<= n 1) 1 (* n (factorial (- n 1)))).
'let' is used to create local variables while 'setq' is used to set the value of an existing variable. 'let' creates a new lexical environment, whereas 'setq' does not.
'car' and 'cdr' are used to access the elements of a list. 'car' returns the first element of the list, while 'cdr' returns all elements except the first one.
In Lisp, a function is defined using the 'defun' keyword. For example, a function to add two numbers would be defined as: (defun add-two-numbers (a b) (+ a b)).
The basic data types in Lisp include: integers, floating-point numbers, characters, symbols, cons cells, lists, vectors, hash-tables, and strings.
This can indicate how quickly they will be able to become productive in a new Lisp development role.
This is important for writing efficient and effective code in any language, including Lisp.
Experience with real-world projects can demonstrate the candidate's ability to apply their Lisp knowledge in practical situations.
This will show their ability to think logically and solve problems, which is crucial for any programming role.
Lisp is a functional programming language, so a strong understanding of functional programming is key to being effective in Lisp.
This is essential as it forms the basis of their ability to write, understand, and debug Lisp code.
The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.
Tail recursion in Lisp is a form of recursion where the recursive call is the last operation in the function. It is important because it allows the Lisp interpreter to optimize the recursion, saving stack space.
'load' is used to load a file and execute its contents, regardless of whether it has been loaded before. 'require' is used to load a file only if it hasn't been loaded before.
Exceptions in Lisp can be handled using the 'condition-case' function. It takes three arguments: a variable to bind the error data, the body of code to execute, and a list of handlers for different types of errors.
Macros in Lisp are used to define new syntax or new control structures. They are functions that operate on code to produce new code, which is then compiled and executed.
A lambda function in Lisp is an anonymous function. It can be defined using the 'lambda' keyword. For example, a lambda function to add two numbers would be: (lambda (a b) (+ a b)).
A skilled Lisp engineer should possess problem-solving abilities, deep understanding of Lisp and other functional programming concepts, and experience with code optimization. Red flags would include inability to explain complex code or lack of hands-on Lisp coding experience during the practical assessment part of the interview.
(defun square (n) (* n n))(defun factorial (n) (if (<= n 1) 1 (* n (factorial (- n 1)))))(mapcar #'(lambda (x) (* x x)) '(1 2 3 4 5))(defun parallel (proc1 proc2) (let ((t1 (make-thread proc1)) (t2 (make-thread proc2))) (thread-join t1) (thread-join t2)))(defclass point () ((x :initarg :x :accessor point-x) (y :initarg :y :accessor point-y)))(defun fib (n) (if (or (= n 0) (= n 1)) n (+ (fib (- n 1)) (fib (- n 2))))) (fib 6)The final few interview questions for a Lisp candidate should typically focus on a combination of technical skills, personal goals, growth potential, team dynamics, and company culture.
Advantages of using Lisp include its expressive syntax, powerful features like macros and first-class functions, and the ability to dynamically modify running programs. Disadvantages include its relatively steep learning curve, lack of widespread use, and limited availability of libraries and frameworks compared to other languages.
A binary search tree in Lisp could be implemented as a nested list, where each node is a list of three elements: the value, the left subtree, and the right subtree. Functions would then be needed to insert, delete, and search for values in the tree.
CLOS is the object-oriented programming system provided by Common Lisp. It provides features such as multiple inheritance, multi-methods, method combination, and meta-object protocol.
Higher-order functions in Lisp are functions that can take other functions as arguments or return functions as results. For example, the 'mapcar' function applies a given function to each element of a list and returns a list of the results.
Lisp has several types of lists, including: proper lists, which are either empty or have a proper list as their tail; dotted lists, which have a non-list value as their tail; and circular lists, which have themselves as their tail.
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