Dear Professor: My name is Carlos Alexandre Grimaldi. I'm engineering student at Federal University of Rio de Janeiro, Brazil. I began my studies in Haskell, and I have some doubts which I report here. I'm very gratefully if you could help me. I'm following a book I downloaded from Internet: "A Gentle Introduction to Haskell, Version 98". Following this, I face some problems: - "inc :: Integer -> Integer" don't work - "inc n = n+1" don't work too; - "data Bool = False | True" also...; - "data Color = Red | Green | Blue | Indigo | Violet" also fails. I thought that this commands and definitions must be inside a program, and don't at prompt "prelude>". So, I opened other book, also downloaded from Internet: "The Hugs 98 User Manual", and I tryed: "module Fact where fact :: Integer -> Integer fact n = product [1..n]" thinking that would be created a file "Fact", in which the definitions for "fact" would work. But this also yield an error... So, I ask you: - is necessary the creation of a file where that definitions could work? - is this file a ".hs"? - how can I create a file like this? Which command or editor? - or, if I wrong, why that examples don't work? Thank you very much for your help. Best regards, Carlos A. Grimaldi.