I am getting a parse error on input '=' when trying to run the following code
module GiveNums
where
import System.IO
main = do
hSetBuffering stdin LineBuffering
n <- giveNum
sum = map (+) n
putStrLn "The sum is " ++ show sum
giveNum = do
hSetBuffering stdin LineBuffering
putStrLn "Enter num"
num <- getLine
if read num == 0
then return []
else do
rest <- giveNum
return ((read num :: Int: rest)
To answer your question: because your code has syntax error.
Some additional comments:
You don't need module when working with a single code file. module is for writing a library.
Bindings in main :: IO () need let because it is in the IO Monad. Read more about do here
Setting stdin buffering mode only once is enough.
There is a sum function in Prelude.
I tried to make the code as close to the original as possible. However, this is not good Haskell code.
import System.IO
main :: IO ()
main = do
hSetBuffering stdin LineBuffering
n <- giveNum
let summation = sum n
putStrLn $ "The sum is " ++ show summation
giveNum :: IO [Int]
giveNum = do
putStrLn "Enter num"
num <- read <$> getLine
if num == 0
then return []
else do
rest <- giveNum
return $ num: rest
Output:
$ runhaskell givenum.hs
Enter num
1
Enter num
2
Enter num
3
Enter num
0
The sum is 6
Because if you want to "assign" something in a do statement you need to put let before it, so sum = map (+) n turns into let sum = map (+) n, but as wizzup pointed out sum is already defined as a standard function and also let sum = map (+) n wont return the sum of integers in n , for that you would need foldr
let sumOfn = foldr (+) 0 n
But it would be easier to do let sumOfn = sum n
Also, let f =map (+) n creates a list of functions of type Int->Int, if n is [1,2,3] then f is [(+1),(+2),(+3)].
let var = expr. Also:map (+) nwon't give a single number but a list of functions, you probably want fold. Also:f x :: ty : xswon't parse right you need parens such as(f x :: ty) : xs).sumis already taken as a variable name, it's the name of a function. Do a:t sumand a:i sumin ghci, or search it. I'd suggest that you comment out yourmainfunction for now and get yourgiveNumfunction working. It's really close to working, especially with Thomas' last suggestion. Then, oncegiveNumworks, start onmain.