On Sun, 31 Aug 2008, Adrian Hey wrote:
Thanks for taking the time to do this Dan. I think the safety requirement has been met, but I think it fails on the improved API. The main complaint would be what I see as loss of modularity, in that somehow what should be a small irrelevant detail of the implementation of some obscure module somewhere has propogated it's way all the way upto main.
That's the key point, as I see it - they aren't "irrelevant details of the implementation", they are requirements the implementation places on its context in order for that implementation to be correct. So they should be communicated appropriately.
To me this seems completely at odds with what I thought was generally accepted wisdom of how to write good maintainable, modular software. Namely hiding as much implemention detail possible and keeping APIs as simple and stable as they can be. I don't know if I'm alone in that view nowadays.
It's no problem to hide implementation detail, but I don't think you should hide the *requirement* of the implementation that it has constraints on how it is called, namely that it requires once-only initialisation or whatever.
Purists aren't going to like it, but I think folk *will* be using "real" global variables in I/O libs for the forseeable future. Seems a shame that they'll have to do this with unsafePerformIO hack though :-(
From a "purist" point of view, it's a shame that they choose to do it at all :-)
Ganesh