Consider the following program.

module Main where

import Data.Array.Repa

data Stuff = !(Array U DIM1 Double) `With` !Double deriving Show

through :: Maybe Double -> Stuff -> Stuff
m `through` (a `With` _) =
  let b = a +^ (negate `smap` sumS (extend (Z :. All :. (1 :: Int)) a))
      c = maybe b (const (negate `smap` a)) m in
      computeUnboxedS c `With` sumAllS b

main :: IO ()
main = print $ Just 1 `through` (fromListUnboxed (Z :. 1) [1] `With` 1)

It should produce the following result once run.

AUnboxed (Z :. 1) (fromList [-1.0]) `With` 0.0

However, when built using repa-3.4.0.1 and compiled with the options -O3 -Wall -funfolding-keeness-factor1000 -funfolding-use-threshold1000, it crashes as follows.

Main: Oops!  Entered absent arg arr2 Array D DIM1 Double

Adding -fno-strictness to the compiler options or removing strictness annotations from the code makes the problem disappear, so this looks like a strictness analyzer problem.

The libraries used were

• QuickCheck-2.8.1,
• array-0.5.1.0,
• base-4.8.1.0,
• bytestring-0.10.6.0,
• containers-0.5.6.2,
• deepseq-1.4.1.1,
• ghc-prim-0.4.0.0,
• integer-gmp-1.0.0.0,
• pretty-1.1.2.0,
• primitive-0.6,
• random-1.1,
• repa-3.4.0.1,
• template-haskell-2.10.0.0,
• tf-random-0.5,
• time-1.5.0.1,
• transformers-0.4.2.0 and
• vector-0.10.12.3.