Thanks, I wasn't aware of vinyl and compdata. I'll check them out.
I'm not very familiar with HList, but I was under the impression that it
provided intersection, not union, i.e. for every type in { x1 x2 ..}, an
HList has an element vs for SOME type in {x1 x2 ..} a Union has an
element..
On Sat, Jun 7, 2014 at 3:18 PM, Carter Schonwald wrote: There's also compdata On Saturday, June 7, 2014, Ben Foppa 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?