--text follows this line-- I'm trying to learn Haskell from YAHT. My attempt at a solution of Exercise 3.10 is failing with a "Type does not match" error. The exercise is to write a function that will read numbers (one per line) from the command line, until the number 0 is entered. At this point the program is supposed to print out the sum of the numbers, their product, and for each number, the factorial. The interaction should resemble this: Give me a number (or 0 to stop): 5 Give me a number (or 0 to stop): 8 Give me a number (or 0 to stop): 2 Give me a number (or 0 to stop): 0 The sum is 15 The product is 80 5 factorial is 120 8 factorial is 40320 2 factorial is 2 The code I have for this is given next (the line that fails is indicated by a comment): module Main where import IO main = do hSetBuffering stdin LineBuffering numberList <- getList let s = sumList numberList let p = prodList numberList putStrLn ("The sum is " ++ s) putStrLn ("The product is " ++ p) printFact numberList fact 0 = 1 fact 1 = 1 fact x = x * fact x - 1 sumList [] = 0 sumList (x:xs) = x + sumList xs prodList [] = 1 prodList (0:xs) = 0 prodList (x:xs) = x * prodList xs printFact [] = return printFact (x:xs) = do -- triggers error message putStrLn (x ++ " factorial is " ++ fact x) printFact xs return getList = do putStrLn "Give me a number (or 0 to stop):" numString <- getLine let num = read numString if num == 0 then return [] else return (num:getList) Here's the full error I get (from HUGS): IO> :l Ex3_10 ERROR "./Ex3_10.hs":28 - Type error in generator *** Term : printFact xs *** Type : b -> c b *** Does not match : IO a If anyone can explain to me how to fix this error I'd appreciate it. Also, what is the difference between <- and let? Lastly, any comments on any other detail of the code, particularly coding, style are most welcome. Thanks! kj