[Chart] A bunch of features and fixes.

[Malcolm Wallace]

> Mon Oct 31 03:42:49 EST 2011 malcolm.wallace at me.com
>  * Fix a missing pattern-match crash.
> 
> This patch (alone) doesn't actually compile. It needs some type constraints propagated across several functions. I suspect these changes are embedded in one of the other patches.
> 
> I've pushed an alternate fix, that returns a Nothing pick value (rather than a default of 0) and doesn't need the additional type constraints.

I expect you are correct about the type constraints being recorded in a different patch.  I guess returning a Nothing value is probably the better choice here in any case.

> Tue Jan 11 23:51:52 EST 2011  malcolm.wallace at me.com
>  * New function stackLayout1sVertically.
> 
> Is it actually desirable that the y-axes share the same type? Or is that just a side effect of the implementation? I wonder if the same GUI output could be generated from a function with the (more versatile) signature of:
> 
> stackLayout1sVertically :: (Ord x,Ord y) => [AnyLayout1 x] -> Renderable ()

All of my charts have their y-axis fixed to Double, so I did not seriously investigate lifting this restriction.  What you suggest seems like a reasonable generalisation.

Regards,
    Malcolm