@deessejs/fp

Functional Programming Utilities for TypeScript

@deessejs/fp provides lightweight, type-safe functional programming utilities. Built for simplicity and first-class integration with @deessejs/errors.

Packages

Package	Description
packages/fp	Core FP utilities: Result, Maybe, Unit
apps/web	Documentation site

Packages

@deessejs/fp

npm install @deessejs/fp @deessejs/errors

import { ok, err, some, none, maybe } from '@deessejs/fp';

// Result - handle errors explicitly
const divide = (a: number, b: number) =>
  b === 0 ? err('Division by zero') : ok(a / b);

const result = divide(10, 2);
result.match({
  ok: (value) => console.log(`Result: ${value}`),
  err: (error) => console.error(`Error: ${error}`),
});

// Maybe - handle optional values safely
const user = { name: 'Alice', address: { city: 'Paris' } };
const city = maybe(user.address?.city)
  .map(c => c.toUpperCase())
  .getOrElse('Unknown');

Getting Started

Prerequisites

• Node.js 20+
• pnpm 10+

Installation

pnpm install

Available Scripts

Workspace (root)

Command	Description
pnpm build	Build all packages
pnpm test	Run all tests
pnpm lint	Lint all packages

Package: fp

pnpm --filter @deessejs/fp build         # Build the package
pnpm --filter @deessejs/fp test          # Run tests (watch mode)
pnpm --filter @deessejs/fp test:run      # Run tests (single run)
pnpm --filter @deessejs/fp type-check    # TypeScript type checking
pnpm --filter @deessejs/fp lint          # Run ESLint

App: web

pnpm --filter web dev      # Start development server
pnpm --filter web build   # Build for production
pnpm --filter web lint    # Run ESLint

CI/CD

Each package has its own GitHub Actions workflows in .github/workflows/:

Workflow	Description
Lint	Runs ESLint
Type Check	Runs TypeScript type checking
Tests	Runs Vitest
Build	Builds the package/app

Tech Stack

• Package Manager: pnpm
• Build Tool: Turborepo
• Language: TypeScript
• Testing: Vitest
• Linting: ESLint
• App Framework: Next.js (React)