Example of using new Vinyl ElField (open universe field types)

Main.hs

{-# LANGUAGE DataKinds, FlexibleContexts, TypeOperators #-}

module Main where

import Data.Proxy
import Data.Vinyl
import Data.Vinyl.Derived
import Data.Vinyl.Functor
import Control.Applicative

foo :: Proxy '("foo", String)
foo = Proxy

bar :: Proxy '("bar", Int)
bar = Proxy

type Fields = ['("foo", String), '("bar", Int)]

rec1 :: FieldRec Fields
rec1 = (foo =: "Hello")
      <+> (bar =: 2)
      <+> RNil

main :: IO ()
main = do
  putStrLn $ printBaz rec1

printBaz :: ('("foo", String) ∈ fields) => FieldRec fields -> String
printBaz = getField . rget foo

setBar :: ('("bar", Int) ∈ fields) => FieldRec fields -> Int -> FieldRec fields
setBar fields v = rreplace (bar =: v) fields