Popularity
8.2
Growing
Activity
6.7
Growing
43
3
5

Monthly Downloads: 453
Programming language: Haskell
License: MIT License
Tags: Other    
Latest version: v0.7.0.0

first-class-families alternatives and similar packages

Based on the "Other" category

Do you think we are missing an alternative of first-class-families or a related project?

Add another 'Other' Package

README

First-class type families Hackage Build Status

For example, consider this simple type family:

type family   FromMaybe (a :: k) (m :: Maybe k) :: k
type instance FromMaybe a 'Nothing  = a
type instance FromMaybe a ('Just b) = b

With first-class-families (fcfs), it translates to a data declaration and instances for a single Eval family:

import Fcf

data FromMaybe :: k -> Maybe k -> Exp k
type instance Eval (FromMaybe a 'Nothing)  = a
type instance Eval (FromMaybe a ('Just b)) = b

That way, the FromMaybe constructor can be partially applied, and passed to higher-order fcfs such as Map:

Eval (Map (FromMaybe 0) '[ 'Just 1, 'Nothing ])  =  '[ 1, 0 ] :: [Nat]

Essential language extensions:

{-# LANGUAGE
    DataKinds,
    PolyKinds,
    TypeFamilies,
    TypeInType,
    TypeOperators,
    UndecidableInstances #-}

See also

Haskell with only one type family (blogpost)


Contributions are welcome. Feel free to open an issue or make a PR on Github!