# simple program crash (GHC 5.02, Hugs)

**Max A.K.
**
max630@mail.ru

*Sat, 22 Dec 2001 09:55:16 +0600*

On Fri, Dec 21, 2001 at 04:22:42PM -0600, Oleg Galbert wrote:
>* test n cosx
*>* | n==0 = cosx
*>* | otherwise = test (n-1) (cosx+cos(cosx))
*
Functions by default are lazy, i.e. they does not compute
the number, but make a note to do it later. In the example
you presented, the value of cosx is not needed until the call
for "test (n-1) (cosx+cos(cosx))". So, as a result of
"test 10000000 0.0" you get a (...+cos(0.0+cos(0.0)))...).
That's not surprising it crashes the program.
>* test1 n cosx
*>* | n==0 = cosx
*>* | otherwise = cosx `seq` test1 (n-1) (cosx+cos(cosx))
*
Here, you make sure that cosx is counted up to a number.
This function works OK.
read http://haskell.org/ghc/docs/latest/set/faster.html
>* main = print ( test 10000000 0.0 )
*
>* Oleg Galbert
*
Max.