[plt-scheme] graphics states and Scheme

Maybe of interest:
Functional Geometry. http://www.frank-buss.de/lisp/functional.html


On 7/4/07, Eli Barzilay <eli at barzilay.org> wrote:
> On Jul  4, Dave Griffiths wrote:
> > [...]  The main thing is the scene description langauge, which
> > currently involves an implicit state stack, and lots of small simple
> > functions. [...]
>
> I'm not sure that this is a proper suggestion, but I'll go anyway.
>
> The thing is that when people use imperative code, they tend to forget
> that using closures it's possible to push the imperative code into a
> functional container.  Here's a very simplified example -- assume that
> this is your imperative library:
>
>   (define current-color 'black)
>   (define (set-color! c) (set! current-color c))
>   (define (draw-line len) (printf "drawing a ~a pixel ~a line\n" color len))
>
> and you define
>
>   (define (draw-cube len color)
>     (set-color! color)
>     (draw-line len)
>     (draw-line len)
>     (draw-line len)
>     (draw-line len))
>
> Instead of draw-cube, you can make it into a thunk that encapsulates
> these operations:
>
>   (define (build-cube len color)
>     (lambda ()
>       (set-color! color)
>       (draw-line len)
>       ...))
>
> Once you have that, the rest becomes natural, for example:
>
>   (define (combine/offset obj1 obj2 ofs)
>     (lambda ()
>       (obj1)
>       (move-by ofs)
>       (obj2)))
>   (define (big-cube color)
>     (build-cube 100 color))
>   (define (rgb-cubes)
>     (let ([r (big-cube 'red)]
>           [g (big-cube 'green)]
>           [b (big-cube 'blue)])
>       (combine/offset (combine/offset r g 50)
>                       b 50)))
>
> --
>           ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
>                   http://www.barzilay.org/                 Maze is Life!
> _________________________________________________
>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>


-- 
Cheers,

Stephen



--
Stephen De Gabrielle
s.degabrielle at ucl.ac.uk
Telephone +44 (0)20 7679 5242 (x45242)
Mobile                  079 851 890 45
http://www.uclic.ucl.ac.uk/annb/MaSI.html
University College London Interaction Centre
Remax House - 31/32 Alfred Place
London - WC1E 7DP