Broken ArrowLoop Instance

[RiugaBachi]

A rec block inside VarT will cause an infinite cyclic reference crash, even for simple cases where the variable is fed constant input and is not referenced outside rec. Tested over both IO and Identity. Below is a minimal complete example. Compiler is GHC 8.6.5 using base 4.12.0.0.

module Main where

import Control.Varying.Core
import Control.Varying.Event
import Control.Arrow
import Data.Functor.Identity

main :: IO ()
main = do
  testVarOver testVar [5.0]
  where
    testVar :: VarT IO Double (Maybe Double)
    testVar = proc val -> do
      rec _ <- returnA -< 0.5
      returnA -< Just 5.0

For reference, the equivalent of the above runs fine in wires.

[schell]

Thanks for the report @RiugaBachi, I'll see how it was implemented in wires.

[schell]

Pattern matching inside 'loop' was a bit too strict, is all. I should have a new version up on hackage soonish. Thanks!