[Haskell-cafe] open-union

[Carter Schonwald]

There's also compdata

On Saturday, June 7, 2014, Ben Foppa <benjamin.foppa at gmail.com> wrote:

> Hi cafe. On a use case whim, I made the open-union package (
> https://github.com/RobotGymnast/open-union), copying the basic idea from
> extensible-effects:Data.OpenUnion1. I haven't uploaded to hackage yet, on
> the chance that there's already something like this around. Here's the
> basic functionality:
>
> {-# LANGUAGE TypeOperators #-}
> {-# LANGUAGE ScopedTypeVariables #-}
> import Data.OpenUnion
>
> type MyUnion = Union (Char :| Int :| [()] :| Void)
>
> showMyUnion :: MyUnion -> String
> showMyUnion
>     =  (\(c :: Char) -> "char: " ++ show c)
>     @> (\(i :: Int) -> "int: " ++ show i)
>     @> (\(l :: [()]) -> "list length: " ++ show (length l))
>     @> typesExhausted
>
> main :: IO ()
> main = do
>     putStrLn $ showMyUnion $ liftUnion (4 :: Int)
>     putStrLn $ showMyUnion $ liftUnion 'a'
>     putStrLn $ showMyUnion $ liftUnion [(), ()]
>
>
> If any of the (@>) cases is omitted, a compile-time error occurs. If you
> try to lift a bad value to the union, a compile-time error occurs.
>
> Any thoughts? Is there already something like this around?
>
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