#5571: factorial.hs:3:12: Parse error in pattern: n + 1
--------------------------+-------------------------------------------------
Reporter: francisco | Owner:
Type: bug | Status: new
Priority: normal | Component: GHCi
Version: 7.0.3 | Keywords:
Testcase: | Blockedby:
Os: Linux | Blocking:
Architecture: x86 | Failure: GHCi crash
--------------------------+-------------------------------------------------
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
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5571>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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