Hi Barry, You can use read: ... lst <- getline median (read lst::[Int]) ... You will have to enter your list like this at the prompt:
[1,2,3,4]
read transforms Strings into some other type (usually specified by a type annotation). read :: Read a => String -> a HTH Chris. On Wed, 20 Aug 2008, Barry Burd wrote:
In the last line of this program, I get the following error message (from ghci)...
Couldn't match expected type `Int' against inferred type `Char' Expected type: [Int] Inferred type: String In the first argument of `median', namely `lst' In the expression: median lst Failed, modules loaded: none.
Here's the program...
module Main where
import IO
lessThan :: Int -> [Int] -> [Int] lessThan x lst = filter (< x) lst
greaterThan :: Int -> [Int] -> [Int] greaterThan x lst = filter (> x) lst
numLessThan :: Int -> [Int] -> Int numLessThan x lst = length (lessThan x lst) numGreaterThan :: Int -> [Int] -> Int numGreaterThan x lst = length (greaterThan x lst)
numLessGreater :: Int -> [Int] -> (Int, Int) numLessGreater x lst = (numLessThan x lst, numGreaterThan x lst)
isMedian :: (Int, Int) -> Bool isMedian (x, y) = x == y
medians :: [Int] -> [Int] medians lst = [x | x <- lst, isMedian (numLessGreater x lst)]
median :: [Int] -> Int median lst = case medians lst of -- All the values in the result are the same, we just pick the first one x:xs -> x
main = do putStr "Enter a list: " lst <- getLine median lst
I'm sure this is because Haskell isn't automatically changing a String to a List of numbers. But how can I do this? Thanks.
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