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.