Calculate fib n in compile time with TemplateHaskell

Fib.hs

{-# LANGUAGE TemplateHaskell #-}
module Fib where

import Language.Haskell.TH
import Language.Haskell.TH.Syntax

fib' :: Int -> Int
fib' n
    | n <= 2 = 1
    | otherwise = fib' (n - 1) + fib' (n - 2)

fib :: Int -> Q Exp
fib n = [| $(lift $ fib' n) |]

-- more : http://stackoverflow.com/questions/9243794/evaluating-a-function-at-compile-time-with-template-haskell

Test.hs

{-# LANGUAGE TemplateHaskell #-}

import Fib

main = print $(fib 40){-# LANGUAGE TemplateHaskell #-}

import Fib

main = print $(fib 40)