Fibonacci数列两种实现方式效率比较

Fibonacci_campare.txt

keliven@keliven:~/haskell_example$ cat fib_3.hs
import System.Environment

fib = 0:1:(zipWith (+) fib (tail fib))
 

main = do
  args <- getArgs
  print $ (fib !!) $ read $ args !! 0

keliven@keliven:~/haskell_example$ cat fib_4.hs
import System.Environment
 
fib :: Int -> Int
fib 0 = 0
fib 1 = 1
fib n = (fib (n-1)) + (fib (n-2))

main = do
  args <- getArgs
  print $ fib $ read $ args !! 0




keliven@keliven:~/haskell_example$ time ./fib_4 50
12586269025

real 2m55.257s
user 2m54.988s
sys 0m0.000s
keliven@keliven:~/haskell_example$ time ./fib_3 50
12586269025

real 0m0.003s
user 0m0.000s