parse error on input `=' Perhaps you need a 'let' in a 'do' block?

Question

When i was writing my first program in Haskell i got this as an error.Please help me.Here's the code:

main = do {
  n <- getLine;
  getInt :: String -> Int;
  getInt n = digitToInt n;
  if n == 2 then print("NO");
    else if n % 2 then print("NO");
         else print("YES");
         }

I would say try to spend another 20 minutes reading about Haskell. — Stefan Dorn, Feb 17 '22 at 17:30
What resource are you using? You seem to be generating vaguely Haskell-like code and seeing what sticks rather than following any sort of tutorial or lesson. — chepner, Feb 17 '22 at 17:31
if i want to learn something i just google it.I don't have any resource that i learn from.If you have one please recommend it to me. — N1kto _ 0, Feb 17 '22 at 17:37
You can use a search engine to find beginner's guides to a language as well. — chepner, Feb 17 '22 at 18:01
Does this answer your question? https://stackoverflow.com/questions/1012573/getting-started-with-haskell — David Lukas, Feb 17 '22 at 18:09

Andreas Molitor · Answer 1 · 2022-02-18T12:14:37.633

Not sure why there are 2 cases for 2 and presumably modulo 2 but here goes a version that compiles and hopefully does what you intended it to do.

main = do
  line <- getLine
  let n = read line
  if n == 2
    then print("NO")
    else if n `mod` 2 == 0
      then print("NO")
      else print("YES")

This could be written a lot more concisely but I attemped to stay as close as possible to your version.

Takeaways:

You don't need semicolons in Haskell at all
You seem to want to redeclare n from a String to an Int. In Haskell you do not mutate variables but create new independent ones instead. Also, if you want to declare variables inside of your function use "let" (only in do blocks), "let" .. "in" or "where"
digitToInt and % are not the functions you are looking for. Tip: Look for functions by name or signature on hoogle

Hope I could help.

You're basically doing `read (read line)`. That's not going to work. — Joseph Sible-Reinstate Monica, Feb 17 '22 at 21:38

parse error on input `=' Perhaps you need a 'let' in a 'do' block?

1 Answers1