On Fri, Nov 30, 2012 at 11:05:41PM +0000, Gábor Lehel wrote:
Well, I'm not so sure it's a great idea to just bake "what GHC does at this moment" (for any particular extension) into the standard without really thinking about it. Even then, you have to figure out, in great detail, what GHC does, and write it all down! That's not negligible effort, either.
And that is the core of the problem. The standard isn't just a list of approved features. It needs to describe them in such detail that a programmer can tell, from the Report alone, whether a particular program is legal, and if so what it's supposed to do. We don't have that level of description for these extensions, and creating it will be a lot of hard work. Relying on "what GHC does at the moment" has obvious risks for programmers, it also puts an unfair responsibility on GHC itself. How can they improve a feature if it's current implementation is the "standard"?