Category Theory in Computing

Table of Contents

Introduction

Category theory provides a unifying mathematical framework for understanding computation, types, and program structure through objects, morphisms, and their compositions.

Fundamental Structures

Categories, Functors, Natural Transformations

diagram-category-hierarchy.png

Commutative Diagrams

diagram-functor-composition.png

Monad Structure

diagram-monad-operations.png

Categorical Patterns in Programming

The Expression Problem

diagram-expression-problem.png

Free Monads and Interpreters

diagram-free-monad-flow.png

Strange Loops and Self-Reference

diagram-strange-loop.png

Implementation in Scheme

Category as Record

(define-record-type <category>
  (make-category objects morphisms compose identity)
  category?
  (objects category-objects)
  (morphisms category-morphisms)
  (compose category-compose)
  (identity category-identity))

(define (functor-map F f)
  "Apply functor F to morphism f"
  ((functor-fmap F) f))

Verification Pattern

diagram-category-verification.png

Applications

  • Type systems (Hindley-Milner as adjunction)
  • Functional reactive programming
  • Database query optimization
  • Concurrent and distributed systems
  • Effect systems and algebraic effects

Resources

  • Categories for the Working Mathematician (Mac Lane)
  • Category Theory for Programmers (Milewski)
  • Seven Sketches in Compositionality (Fong & Spivak)

Author: Jason Walsh

jwalsh@nexus

Last Updated: 2026-05-19 20:37:57

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