A Copilot specification involving an update to a struct containing arrays

StructsOfArrays.hs

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE NoImplicitPrelude #-}
module Main (main) where

import Language.Copilot
import Copilot.Compile.C99

data SoA = SoA
  { arr :: Field "arr" (Array 2 Word32)
  }

instance Struct SoA where
  typeName _ = "soa"
  toValues soa = [Value typeOf (arr soa)]

instance Typed SoA where
  typeOf = Struct $ SoA $ Field undefined

spec :: Spec
spec = do
  let soa :: Stream SoA
      soa = constant $ SoA $ Field $ array [0, 0]

  trigger
    "arrays"
    ((((soa #! arr) (constant (array [1, 2])) # arr) .!! 0) ==
     (((soa #! arr) (constant (array [2, 1])) # arr) .!! 1))
    [arg soa]

main :: IO ()
main = do
  spec' <- reify spec
  compile "structs_of_arrays" spec'