Home/ Questions/Q 105611
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-11T01:27:59+00:00

I wrote this snippet of code and I assume len is tail-recursive, but a

  • 0

I wrote this snippet of code and I assume len is tail-recursive, but a stack overflow still occurs. What is wrong?

myLength :: [a] -> Integer  myLength xs = len xs 0     where len [] l = l           len (x:xs) l = len xs (l+1)  main = print $ myLength [1..10000000]
Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Remember that Haskell is lazy. Your computation (l+1) will not occur until it’s absolutely necessary.

    The ‘easy’ fix is to use ‘$!’ to force evaluation:

    myLength :: [a] -> Integer myLength xs = len xs 0 where len [] l = l       len (x:xs) l = len xs $! (l+1)        main = print $ myLength [1..10000000]
    • 0