Ashley Yakeley wrote:
On Fri, 2009-07-24 at 12:13 +0100, Jules Bean wrote:
When this actually alters the integer inside my Micro, I'm going to be pretty surprised.
Or maybe I'm not that surprised, but the point is, it exposes the internals of Fixed. It's an abstraction hole.
The whole point of SYB is to break abstraction. A "subterm" is a rather vague concept, and it makes a rather arbitrary distinction between "loosely holding" the contained value (will be touched by 'everywhere') and "tightly using" it (won't be touched).
I disagree with you entirely and completely. I've made my argument and there is nothing more to add. You can ignore it if you wish. The whole point of SYB is not to break abstraction. A Data instance for Data.Fixed which exposes the Integer inside would render it useless for the kind of things I expect people do with SYB. Jules