On Thu, Nov 26, 2009 at 8:37 PM, Zsolt Ero <zsolt.ero@gmail.com> wrote:

Sorry to ask such a basic question here, but I am trying to write my
first Haskell OpenGL animation and just encontered with thsese
questions:

Could someone point me to some help on how does "do" work and how does
preservingMatrix?

I am trying to write a program starting from the OpenGL tutorial on
the wiki, but I never used do's before.

My very basic question is that how do I generally repeat a command
many times? I understand "do" can do it, but it's not clear to me how
to use it and how it works.

So if I would like to write the following in one line, how could I write it?:
spiral 0.7
spiral 0.8
spiral 0.9
spiral 1.0

I don't understand in which cases I can use "map something
[0.7,0.8..1]" and in which cases I need do and how could I map using
do.

>From the tutorial, I could write this line, which works, but I don't
really know what does mapM_ and preservingMatrix do.

mapM_ (\x -> preservingMatrix $ do
scale x x (1::GLfloat)
rotate (x*(200)) $ Vector3 0 0 (1::GLfloat)
spiral ((sin(a/50))^2/2+0.5)
) $ ([0.5,0.6..1::GLfloat])

Zsolt
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