18 Apr
2007
18 Apr
'07
1:25 a.m.
On Wed, Apr 18, 2007 at 01:47:04AM +0100, Neil Mitchell wrote:
- If we permit undecidable instances, one may assign numerals to types. This gives us total order and hence comparison on types. In this approach, we only need N instances to cover N types. This is still better than Typeable because the equality is decided and can be acted upon at compile time.
In my particular case whether I act at compile time or run time is unimportant, but obviously this is an important advantage in general. Unfortunately a cost of one instance per type is still higher than I'd like to pay :-)
Now, it requires one line of code: {-# OPTIONS_DERIVE --derive=TTypeable #-} Stefan