When I write only main = do ... block, it works perfectly. When I put only stories = do... block it also works. Maybe there is an indentation problem.
Here is the code:
stories = do
let str0 = "There once was "
str1 <- ["a princess ", "a cat ", "a little boy "]
let str2 = "who lived in "
return ( str0 ++ str1 )
main = do
let len = length stories
putStrLn ("Enter a number from 0 to " ++ show (len - 1))
n <- readLn
putStrLn ""
putStrLn (stories !! n)
What is wrong with it?
Although this fact is not as advertised as in the case of, say, Python, Haskell does have syntactically significant indentation. In your case the code in the bodies of dos must be indented:
stories = do
let str0 = "There once was "
str1 <- ["a princess ", "a cat ", "a little boy "]
let str2 = "who lived in "
return ( str0 ++ str1 )
main = do
let len = length stories
putStrLn ("Enter a number from 0 to " ++ show (len - 1))
n <- readLn
putStrLn ""
putStrLn (stories !! n)
main inside the do block.