This simple program prints the sum and product of a list of numbers from an input file.
main :: IO ()
main = do
text <- readFile "./input.txt"
print $ sum [read line | line <- lines text]
print $ product [read line | line <- lines text]
{-
Example input:
1
2
3
4
Example output:
10
24
-}
It would be nice to avoid repeating [read line | line <- lines text]. If I extract the function printSumAndProduct, I can use a let expression to do this:
main :: IO ()
main = do
text <- readFile "./input.txt"
printSumAndProduct text
printSumAndProduct :: String -> IO ()
printSumAndProduct text =
let numbers = [read line | line <- lines text]
in do
print $ sum numbers
print $ product numbers
However, I would prefer to just have one function, main. Is it possible to do this without having a separate function printSumAndProduct?
Here's what I've tried:
main :: IO ()
main = do
text <- readFile "./input.txt"
let numbers = [read line | line <- lines text]
in do
print $ sum numbers
print $ product numbers
But this is a syntax error:
main.hs:5:3: error: parse error on input ‘in’