Getting Started

This guide walks you through installing fp-ts and writing your first program.

Installation

# npm
npm install fp-ts

# yarn
yarn add fp-ts

# pnpm
pnpm add fp-ts

fp-ts is a pure TypeScript library with no runtime dependencies.

TypeScript Configuration

fp-ts requires TypeScript’s strict mode to be enabled. Without it, type inference for many combinators will not work correctly.

// tsconfig.json
{
  "compilerOptions": {
    "strict": true
  }
}

Your First Program

Here is a small example using Option to handle a value that might not exist:

import { pipe } from 'fp-ts/function'
import * as O from 'fp-ts/Option'

const inverse = (n: number): O.Option<number> =>
  n === 0 ? O.none : O.some(1 / n)

const result = pipe(
  inverse(2),
  O.map((n) => n * 100),
  O.getOrElse(() => 0)
)

console.log(result) // 50

Option represents a value that is either present (some) or absent (none). Instead of throwing exceptions or returning null, you model the absence explicitly and handle it with combinators like map, fold, and getOrElse.

Import Style

fp-ts modules can be imported individually to keep bundle size small:

// Import a specific module
import * as E from 'fp-ts/Either'
import { pipe } from 'fp-ts/function'

// Or import everything (not recommended for production)
import * as fp from 'fp-ts'

Next Steps

• Browse the API Reference for available modules
• Read the Code Conventions to understand fp-ts patterns
• Explore Learning Resources for tutorials and articles