[Haskell-beginners] factorial question

[KMandPJLynch]

Good afternoon,

I'm going thru Graham Hutton's book "Programming in Haskell" [and am viewing the associated online lectures by Erik Meijer and Graham].
I find both to be excellent.
My problem is with the following statements:

factorial'      :: Int -> Int
factorial'  0    = 1
factorial' (n+1) = (n+1)*factorial' n

When I load this into GHC I get the following error:

pihch01.hs:128:13: Parse error in pattern: n + 1

I'd appreciate any advice.

Good day
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