Unknown call overhead.

Lib.hs

module Lib where

import Data.Vector as V

type LookupCached a = Int -> a
mkCache :: [a] -> LookupCached a
mkCache xs =
  let !cache = V.fromList xs
  in  V.unsafeIndex cache


type CachedList1 a = Vector a
mkCache2 :: [a] -> CachedList1 a
mkCache2 xs = V.fromList xs

lookupCache :: CachedList1 a -> Int -> a
lookupCache !cache !i = V.unsafeIndex cache i

Main.hs

{-# OPTIONS_GHC -O2 -fproc-alignment=64 #-}

import Criterion.Main

import Lib

index = 1 :: Int

-- Our benchmark harness.
main = defaultMain [
  bgroup "vec-cache"
    [ env
        (pure $ mkCache $ [0..1000::Int] )
        (\cache -> bench "higher-order"  $ whnf cache index)
    , env
        (pure $ mkCache2 $ [0..1000::Int] )
        (\cache -> bench "defunctionalized"  $ whnf (lookupCache cache) index)
    ]
  ]