Package Exports

fp-ts
fp-ts/lib/Applicative
fp-ts/lib/Apply
fp-ts/lib/Array
fp-ts/lib/Array.js
fp-ts/lib/Chain
fp-ts/lib/ChainRec
fp-ts/lib/Const
fp-ts/lib/Contravariant
fp-ts/lib/Either
fp-ts/lib/Either.js
fp-ts/lib/EitherT
fp-ts/lib/Extend
fp-ts/lib/Field
fp-ts/lib/Filterable
fp-ts/lib/Foldable
fp-ts/lib/Free
fp-ts/lib/Functor
fp-ts/lib/IO
fp-ts/lib/Identity
fp-ts/lib/Monoid
fp-ts/lib/NonEmptyArray
fp-ts/lib/Option
fp-ts/lib/Option.js
fp-ts/lib/OptionT
fp-ts/lib/Ord
fp-ts/lib/Ordering
fp-ts/lib/Reader
fp-ts/lib/ReaderT
fp-ts/lib/Semigroup
fp-ts/lib/Setoid
fp-ts/lib/State
fp-ts/lib/StateT
fp-ts/lib/Task
fp-ts/lib/These
fp-ts/lib/Traversable
fp-ts/lib/Tuple
fp-ts/lib/Validation
fp-ts/lib/Writer
fp-ts/lib/function

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (fp-ts) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

npm downloads

A mix of

fantasy-land
static-land
PureScript
Scala

See the section "Technical overview" below for an explanation of the technique.

Installation

To install the stable version:

npm install --save fp-ts

Documentation

OptionT
Free

Algebraic types

	Array	Option	Either	NEA(*)	Task	Const	Identity	Validation
Setoid	❌	✅	✅	❌	❌	✅	✅	❌
Semigroup	✅	✅	❌	✅	✅	❌	❌	❌
Monoid	✅	✅	❌	❌	✅	❌	❌	❌
Functor	✅	✅	✅	✅	✅	✅	✅	✅
Contravariant	❌	❌	❌	❌	❌	✅	❌	❌
PointedFunctor	✅	✅	✅	✅	✅	✅	✅	✅
Apply	✅	✅	✅	✅	✅	✅	✅	✅
Applicative	✅	✅	✅	✅	✅	✅	✅	✅
Alt	✅	✅	✅	❌	❌	❌	❌	✅
Plus	✅	✅	❌	❌	❌	❌	❌	❌
Alternative	✅	✅	❌	❌	❌	❌	❌	❌
Foldable	✅	✅	✅	✅	❌	❌	✅	✅
Traversable	✅	✅	✅	✅	❌	❌	✅	✅
Chain	✅	✅	✅	✅	✅	❌	✅	❌
ChainRec	❌	❌	❌	❌	❌	❌	❌	❌
Extract	❌	❌	❌	❌	❌	❌	✅	❌
Extend	❌	✅	✅	❌	❌	❌	✅	❌
Comonad	❌	❌	❌	❌	❌	❌	✅	❌
Bifunctor	❌	❌	✅	❌	❌	❌	❌	❌

(*) NonEmptyArray

Monads

Array
Either
Identity
Option
Reader
State
Task
Writer

Comonads

Identity
Store
Traced

Monad transformers

EitherT
OptionT
ReaderT
StateT

Technical overview

Higher kinded types and type classes

Higher kinded types are represented by a unique string literal (called URI).

There's a central type dictionary where a mapping URI -> concrete type is stored

// file ./HTK.ts
export interface HKT<A> {}

Instances can be defined (everywhere) using a feature called Module Augmentation so there's no danger of name conflict (the typechecker checks for duplicates).

Here's a mapping between the string literal 'Option' and the concrete type Option<A>

// file ./Option.ts
declare module './HKT' {
  interface HKT<A> {
    Option: Option<A>
  }
}

export const URI = 'Option'
export type URI = typeof URI
export type Option<A> = None<A> | Some<A>

export class None<A> {
  readonly _URI: URI
  map<B>(f: (a: A) => B): Option<B> {
    return none
  }
  ...
}

export Some<A> {
  readonly _URI: URI
  // fantasy-land implementation
  map<B>(f: (a: A) => B): Option<B> {
    return new Some(f(this.value))
  }
  ...
}

// static-land implementation
export function map<A, B>(f: (a: A) => B, fa: Option<A>): Option<B> {
  return fa.map(f)
}

Concrete types can be retrieved by their URI using a feature called Index types.

Type classes are implemented following (when possible) both the static-land spec and the fantasy-land spec.

Here's the definition of the type class Functor (following the static-land spec)

export interface Functor<F extends HKTS> {
  URI: F
  map<A, B>(f: (a: A) => B, fa: HKT<A>[F]): HKT<B>[F]
}

License

The MIT License (MIT)