What are first-class functions and first-class citizens in programming?

Can you explain what first-class functions are?

First-class functions are functions that can be treated like any other variable. They can be assigned to variables, passed as arguments, or returned from other functions.

What about first-class citizens? How do they relate to first-class functions?

First-class citizens refer to entities that can be passed around and manipulated like any other data type. In programming, functions are often considered first-class citizens.

Can you give me an example of first-class functions in JavaScript?

Sure! In JavaScript, you can assign a function to a variable and then call it later. For example:

const greet = function(name) {
  return `Hello, ${name}!`;
};
console.log(greet('Alice')); // Outputs: Hello, Alice!

Are there programming languages that don't support first-class functions?

Yes, some older languages or those with a more rigid type system may not support first-class functions. For example, languages like C do not treat functions as first-class citizens.