[Haskell] Creating a factorial function in GHC

[Henning Thielemann]

On Wed, 9 May 2012, Angus Comber wrote:

> I am trying to create a factorial function in GHC.  I am following the
> online learnyouahaskell.com book (specifically types-and-typeclasses
> page).
>
> Bear in mind this is my day 1 of learning Haskell.

Then beginners at haskell.org might be a better place to ask, since
haskell at haskell.org is for announcements.


> The book suggests:
>
> factorial :: Integer -> Integer
> factorial n = product [1..n]
>
> But if I enter first line then press <Enter> I see:
> <interactive>:1:1 Not in scope: 'factorial'
>
> What am I doing wrong?

The code you entered is intended to be the content of a text file that can 
be loaded into GHCi or Hugs. If you want to write it immediately into GHCi 
you may write:

Prelude> let factorial :: Integer -> Integer; factorial n = product [1..n]