factorial.hs:3:12: Parse error in pattern: n + 1

Environment of work

Ubuntu 11.10

$ uname -a
Linux fmgo-HP 3.0.0-12-generic #20-Ubuntu SMP Fri Oct 7 14:50:42 UTC 2011 i686 i686 i386 GNU/Linux

$ ghci
GHCi, version 7.0.3

$gcc -v
....
gcc versión 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3)

---

The problem

---

I composed the function

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

in the file "factorial.hs". So I make {{ $ ghci factorial }}} and then ghci produces the message

GHCi, version 7.0.3: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main             ( factorial.hs, interpreted )

factorial.hs:3:12: Parse error in pattern: n + 1
Failed, modules loaded: none.
Prelude> 

therefore I changed the content of factorial.hs to

fact :: Integer -> Integer
fact 0 = 1
fact n = n * fact (n-1)

now I make

Prelude> :l factorial.hs

obtaining the dialog

[1 of 1] Compiling Main             ( factorial.hs, interpreted )
Ok, modules loaded: Main.
*Main> 

but "the problem" is that the simple computation

*Main> factorial (-1)

produces

*** Exception: stack overflow

In GHCi version 6.10.4 there is no bug ... or problem