Functor

Spicy — senior dev territoryGeneral Dev

ELI5 — The Vibe Check

A functor is a box you can map over. Array? Functor. Optional? Functor. Promise? Functor. If you can apply a function to what's inside without unwrapping the box, congratulations — you've been using functors all along.

Real Talk

A type F that supports a 'map' operation: given F and a function T -> U, produce F. Functors preserve structure — mapping over an array gives an array, mapping over an Option gives an Option. They must obey identity and composition laws. Arrays, Promises, and Options are all functors.

Show Me The Code

// Array is a functor: .map() applies a function inside the 'box'
[1, 2, 3].map(x => x * 2); // [2, 4, 6]

// Option/Maybe is a functor
const name = user?.profile?.name; // mapping through optional chain

When You'll Hear This

"Every time you call .map() on an array, you're using it as a functor." / "Functors are simpler than monads — if you understand Array.map, you understand functors."

Related Terms

Array

An array is a list of things in order, like a numbered row of boxes. Box 0 holds the first item, box 1 holds the second, and so on.

beginnerGeneral Dev

Functional Programming

Functional programming is like cooking with strict rules: no shared bowls, no side dishes contaminating each other, and every dish must be exactly reproduc...

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Monad

A monad is a design pattern for chaining operations that have extra 'context' — like maybe-empty values, async results, or errors.

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Pattern Matching

Pattern matching is like a super-powered switch statement that can look inside data structures and pull out the parts you need.

intermediateGeneral Dev

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