williamareynolds/ts-cat

A static-land and fantasy-land compliant library containing interfaces for common type-classes and common instances of them.

ts-cat

A static-land and fantasy-land compliant library containing interfaces for common type-classes and common instances of them.

This library is currently in very active development. Be aware that changes will be frequent, but that breaking changes will always incur a major version change.

Limitations

Static Interfaces

Be aware that Typescript simply does not support some typing behaviors that would make some things work as expected. The most serious of these issues is that static methods cannot be specified in interfaces. This means that a fantasy-land compliant interface for Applicative cannot be properly created because of can't be enforced as a class method. There is currently an open issue for this here.

Static Types

static-land implementations are limited in their ability to properly type results. This appears to be an issue with typescript, rather than an issue with the implementation. Considering the following demonstration with Identity<number>:

import { identity } from './src/instance/Identity'

const sample = identity.of(5)
const mapped = identity.map(a => a + 5, sample)

In this case, typescript may think the type of mapped is Identity<any>, even though it's actually Identity<number>. If we move the static functions from the identity object to the Identity class as static functions, the type issues are resolved. Unfortunately, we would have to define those static functions on the class, rather than setting them equal to the functions from the identity object. Due to Typescript's lack of static interface declarations, this causes us to lose the value of having an interface for the static functions.

Documentation

fantasy-land

static-land

Theory and Usage

API Docs

ts-cat's Issues

Implement Either Monad

Create a monad for Either which follows the intent of Haskell's Either.

Implement static interface on class

Currently, the static-land compliant interface is implemented on an object currently. This isn't very convenient, but until the following Typescript issue is decided on, this can't be corrected.

microsoft/TypeScript#33892

This issue can be picked up if static interfaces are adopted in Typescript.

Implement an interface for Alt

https://github.com/fantasyland/fantasy-land#alt

Implement an instance of Alt for Maybe.