[bitc-dev] BitFields and Integral typeclass

[Swaroop Sridhar]

I was writing the instances for the integral typeclass:

(deftypeclass (Integral 'a))

For fixed precision primitive integers, the following are the instances 
(I do not have any methods for now):

(definstance (Integral  int8))
(definstance (Integral uint8))
(definstance (Integral  int16))
(definstance (Integral uint16))
(definstance (Integral  int32))
(definstance (Integral uint32))
(definstance (Integral  int64))
(definstance (Integral uint64))

(definstance (Integral (mutable  int8)))
(definstance (Integral (mutable uint8)))
(definstance (Integral (mutable  int16)))
(definstance (Integral (mutable uint16)))
(definstance (Integral (mutable  int32)))
(definstance (Integral (mutable uint32)))
(definstance (Integral (mutable  int64)))
(definstance (Integral (mutable uint64)))

In order to deal with bitfields, I must write a huge number of instances.

(definstance (Integral (bitfield  int8 1)))
(definstance (Integral (bitfield uint8 1)))
(definstance (Integral (bitfield  int8 2)))
(definstance (Integral (bitfield uint8 2)))
...
...

totally 508 instances
...
...
(definstance (Integral (mutable (bitfield  int64 63))))
(definstance (Integral (mutable (bitfield uint64 63))))


This might be another case that motivates literal classes (singleton 
types). Although -- I think -- to a lesser extent than the case of arrays.

My expectation is that bitfields should be used in low level structures, 
and no other class should have all of these instances. If they do, they 
can always inherit the Integral typeclass. Also, it is possible to 
construct a tree of typeclasses for the bitfields obtainable from 
different types which are all inherited by the Integral typeclass.

So, for now I have put in all these instances, and I think we should go 
with them.


Thanks,
Swaroop.