CODEWITHSUNDEEP
c++haskellrecursion
Harris
Harris

Reputation: 11

How to use my recursive function in Haskell?

lol :: IO int
lol = go -1 0 0 0
where go k m n p = case k of
        -1 -> do{
                q <- readLn ;
                go 0 0 0 q
            }
        p -> do{
                putStrLn $ show $ n
            }
        _ -> do{
                q <- readLn ;
                go (k+1) q (if q > m then n+q-m else n) p
                return()
            }

I(a haskell beginner) am doing some practise questions. I have written a recursive function but i don't know how to use it in main. Please help me to do solve this problem. This is my idea in C++ and I got it accepted.

#include<iostream>
using namespace std;
int main(){
    long long int prev=0;
    long long int count,ans=0;
    cin >> count;
    long long int p;
    for(int i=0; i<count ;i++){
        cin >> p;
        if(p>prev){
            ans+=p-prev;
        }
        prev=p;
    }
    cout << ans << endl;
}

Upvotes: 1

Views: 90

Answers (2)

lehins
lehins

Reputation: 9767

How about this. I just translated it directly from C++

module Main where


go :: Int -> Int -> Int -> IO Int
go i prev acc
  | i > 0   = do p <- readLn
                 if p > prev
                   then go (i-1) p (acc + (p - prev))
                   else go (i-1) p acc
  | otherwise = return acc

main :: IO ()
main = do
  count <- readLn :: IO Int
  ans <- go count 0 0
  print ans

Upvotes: 2

Daniel Wagner
Daniel Wagner

Reputation: 152682

There are several syntax errors:

  • add parentheses around negative numbers when using them as arguments
  • to avoid starting a fresh line in the module block, indent where (and all following lines) a little bit
  • add the missing semicolon to the line before return ()

And one type error: you should write lol :: IO (). After fixing these, you may write main = lol to use it (or simply name it main instead of lol). No idea whether it does what it's supposed to do, but that seems like a thing you should be able to test once you get it running.

Upvotes: 2

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