deriving over renamed types

Ashley Yakeley
Fri, 5 Apr 2002 14:54:09 -0800

At 2002-04-04 05:57, C T McBride wrote:

>> ...which would be very useful, but would probably have unpleasant
>> consequences for type inference...
>To my mind, this is not a credible objection. The horse has already
>bolted; there's no point in trying to shut the stable door.

Perhaps I should say "type decidability". Currently Haskell can always 
calculate whether one type-constructor is a substitution-instance of 
another, and therefore whether two type-constructors are the same. This 
may not be possible if you have full type lambdas, as in general there is 
no way of calculating whether two functions are the same.

Ashley Yakeley, Seattle WA