Foldl traverses with State, foldr traverses with anything

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Using reverse breaks fusion:

  findR   expensive fused: OK
    55.6 ns ± 3.5 ns, 671 B  allocated,   0 B  copied, 7.0 MB peak memory
  findR   cheap fused:     OK
    24.0 μs ± 1.8 μs, 312 KB allocated,  12 KB copied, 7.0 MB peak memory

  findR'  expensive fused: OK
    691  ns ±  55 ns, 645 B  allocated,   0 B  copied, 7.0 MB peak memory
  findR'  cheap fused:     OK
    19.1 μs ± 1.6 μs, 156 KB allocated,   9 B  copied, 7.0 MB peak memory

  findR'' expensive fused: OK
    238  ns ±  21 ns, 2.0 KB allocated,   0 B  copied, 7.0 MB peak memory
  findR'' cheap fused:     OK
    130  μs ± 6.8 μs, 937 KB allocated,  44 KB copied, 7.0 MB peak memory

That’s when I add these benchmarks:

  , bench "findR   expensive fused" $ nf (\(x,y,z) -> findR (even . fib) (enumFromThenTo x y z)) (20,19,1 :: Int)
  , bench "findR   cheap fused" $ nf (findR  even . uncurry enumFromTo) (1,10000 :: Int)