CODEWITHSUNDEEP
haskell
Lakshman
Lakshman

Reputation: 479

Writing String and integer to stdout in Haskell

I am new to Haskell and I want to know how to print string and integer value returned by some function in Haskell as we simply do in C++.

#include <iostream>
using namespace std;

int solve(int a) {
  return a * a;
}

int main() {
  int cases, number;
  cin >> cases;

  for (int cs = 1; cs <= cases; cs++) {
    cin  >> number; 
    cout << "Case " << cs << ": " << solve(number) << endl;
  }

  return 0;
}

I tried similar in Haskell but no luck and getting error.

solve :: Int -> Integer
solve = …

main = do
  n <- readLn
  forM_ [1..n] (\i -> do
    m <- readLn
    printf "Case %d: %d" i (solve m))

Upvotes: 0

Views: 3471

Answers (1)

chi
chi

Reputation: 116139

Use forM_ [1..n::Int] to let the compiler know the type you want for n. Otherwise there's not enough information for the readLn to typecheck. 

main :: IO ()
main = do
    n <- readLn
    forM_ [1..n::Int] (\i -> do
        m <- readLn
        printf "Case %d: %d\n" i (solve m))

printf is not so used in Haskell when you do not need its fancy features (e.g. %04d or more complex format strings). A more idiomatic way could be

main :: IO ()
main = do
    n <- readLn
    forM_ [1..n::Int] (\i -> do
        m <- readLn
        putStrLn $ "Case " ++ show i ++ ": " ++ show (solve m)

The function show converts almost anything to a string.

Upvotes: 3

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