Re: Comments on decoration ill, intersection and union

[John Pryce <j.d.pryce@xxxxxxxxxx>]

Folk

On 18 Dec 2012, at 09:54, Jürgen Wolff von Gudenberg wrote:
> There seems to be agreement that decorations concern point functions. And that union and intersection have no corresponding point operation.
> But there seems to be agreement how to use them to define piecewise defined continuous functions.
> So what do you think, if we offer this as an option
> "An implementation may  define propagation of decorations (for
> piecewise defined continuous functions) in the way that
> intersection propagates the max and union propagates the  min" ?
> That makes it more complicated and invokes the danger of misuse
> but it may help to end this dead-ended discussion

Something like that looks reasonable. How about
"An implementation may define additional operations:
  intersectionDec(xx_dx,yy_dy) is as intersection(xx_dx,yy_dy), 
  except that it decorates the result with max(dx,dy).
and
  convexHullDec(xx_dx,yy_dy) is as convexHull(xx_dx,yy_dy), 
  except that it decorates the result with min(dx,dy).
A language may make either the standard operations, or these operations, its default operations for intersection and convexHull."

John