int-index / union

Extensible type-safe unions for Haskell

Union

Extensible type-safe unions.

ghci> let a = openUnion # (5 :: Int) :: OpenUnion '[Bool, Int]

ghci> a ^? openUnion :: Maybe Int
Just 5

ghci> a ^? openUnion :: Maybe Bool
Nothing

ghci> a ^? openUnion :: Maybe Char
<interactive>:8:6:
    No instance for (UElem Char '[] (RIndex Char '[]))
      arising from a use of ‘openUnion’
    In the second argument of ‘(^?)’, namely ‘openUnion’
    In the expression: a ^? openUnion :: Maybe Char
    In an equation for ‘it’: it = a ^? openUnion :: Maybe Char

union's Issues

Documentation

Benchmark build failure: duplicate NFData instance for Proxy

/Users/danburton/scratch/union-0.1.1.0/bench/Benchmark.hs:11:10: error:
    Duplicate instance declarations:
      instance forall k (a :: k). NFData (Proxy a)
        -- Defined at bench/Benchmark.hs:11:10
      instance [safe] forall k (a :: k). NFData (Proxy a)
        -- Defined in ‘Control.DeepSeq’

How I reproduced the error:

stack unpack union-0.1.1.0
cd union-0.1.1.0
stack init --resolver nightly-2016-06-08
stack bench

Vinyl 7.0

I'd like to put vinyl 0.7 on Hackage, but union's dependency constraint on vinyl < 0.7 prevents me from doing that. Is it possible to upgrade to relax constraints either upgrade to vinyl 0.7?

Accidentally wrote the same library

This isn't really an issue, but @mckeankylej just pointed out to me that we inadvertently wrote the same library. In particular, your Union is identical to my CoRec and your lens machinery is identical to my optics. (The typeclass in that module should actually redefine rput, rget, etc. as well, but it looks like I got lazy and forgot to add those).

Prisms

vinyl has lenses, so union can have prisms.

Pattern synonyms

U1, U2, U3, U4, ... U16 for Union
OU1, OU2, OU3, OU4, ... OU16 for OpenUnion

Generate via TH, taking the amount as a parameter.