Package Exports

newtype-ts
newtype-ts/lib/NonNegativeInteger

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Readme

Usage

Newtypes

Let's define a newtype for the EUR currency

import { Newtype, iso } from 'newtype-ts'

interface EUR extends Newtype<{ readonly EUR: unique symbol }, number> {}

// isoEUR: Iso<EUR, number>
const isoEUR = iso<EUR>()

// eur: EUR
const eur = isoEUR.wrap(2)

// n: number
const n = isoEUR.unwrap(eur)

declare function f(eur: EUR): void

f(2) // static error: Argument of type '2' is not assignable to parameter of type 'EUR'
f(eur) // ok

For the Iso type, see the monocle-ts documentation.

An Integer is a refinement of number

import { Newtype, prism } from 'newtype-ts'

interface Integer extends Newtype<{ readonly Integer: unique symbol }, number> {}

const isInteger = (n: number) => n % 1 === 0

// prismInteger: Prism<number, Integer>
const prismInteger = prism<Integer>(isInteger)

// oi: Option<Integer>
const oi = prismInteger.getOption(2)

declare function f(i: Integer): void

f(2) // static error: Argument of type '2' is not assignable to parameter of type 'Integer'
oi.map(f) // ok

For the Prism type, see the monocle-ts documentation.

Builtin newtypes

Integer
Negative
NegativeInteger
NonNegative
NonNegativeInteger
NonPositive
NonPositiveInteger
NonZero
NonZeroInteger
Positive
PositiveInteger

import { NonZero, prismNonZero } from 'newtype-ts/lib/NonZero'

// a total function
const safeDivide = (numerator: number, denominator: NonZero): number => {
  return numerator / prismNonZero.reverseGet(denominator)
}

// result: Option<number>
const result = prismNonZero.getOption(2).map(denominator => safeDivide(2, denominator))

TypeScript compatibility

The stable version is tested against TypeScript 2.9.x

Performance

const double = n => n * 2
const doubleEUR = eurIso.modify(double)

Test double(2) vs doubleEUR(eurIso.wrap(2))

Results (node v8.9.3)

double x 538,301,203 ops/sec ±0.45% (87 runs sampled)
doubleEUR x 536,575,600 ops/sec ±0.27% (87 runs sampled)

Recipes

How to lift a function

const double = (n: number): number => n * 2

// doubleEUR: (s: EUR) => EUR
const doubleEUR = eurIso.modify(double)

How to operate over newtypes

import { over } from 'newtype-ts'

interface USD extends Newtype<'USD', number> {}

const USDFromEUR = (n: number): number => n * 1.18

// getter: Getter<EUR, USD>
const getter = over<EUR, USD>(USDFromEUR)

// usd: USD
const usd = getter.get(eur)

For the Getter type, see monocle-ts documentation.

newtype-ts