[Haskell-cafe] Design question
ajs at 2piix.com
Mon Dec 28 23:56:48 EST 2009
> There are many SVG elements, of which only a few are valid as the
> content of each other SVG elements.
> SvgDocumentElement defines the allowed subset for the SVG document.
> I want to generate a "DList Char" for all those sub-elements and
> finally collapse them to one "DList Char" representing the whole SVG
> So it's a bit more complicated than your "Either" example
I suggest a monadic combinator approach. The grammar's the thing.
> data View a = AtomicView a
> | NestViews (View a) (View a) (View a)
> | ConcatViews (View a) (View a)
> | Etc...
> instance Monad View where
> return = AtomicView
> AtomicView v >>= f = f v
> (NestViews left middle right) >>= f = (ConcatViews (ConcatViews
left middle) right) >>= f
> (ConcatViews left right) >>= f = ConcatVeiws (f left) (f
> -- Etc >>= f = whatever
These are "structural" nodes. Notice how >>= normalizes your document
automagically. You would put your specific node types "in" Etc.
Writing a renderer from something with this form is pretty straight
forward. Enforcing constraints isn't too hard either. Neither is
parsing. Just write a parser for each
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Haskell-Cafe