Nothing forbids you from allowing negative bit positions in a data type,
for instance for fractional bits in a fixed position numeric type.
Consequently, I'm -1 on this proposal.
You can currently construct 0 several ways, e.g. clearBit (bit 0) 0 could
be use to supply a default for any such zeroBits member of the class.
-Edward
On Sun, Feb 16, 2014 at 5:14 AM, Herbert Valerio Riedel
Hello *,
Right now, there seems to be no "defined" way to create a zero 'Bits'-value (w/o requiring also a 'Num' instance), that has all bits cleared without involving at least two operations from the 'Bits' class (e.g. `clearBit (bit 0) 0` or `let x = bit 0 in xor x x`).
OTOH, introducing a new method 'class Bits a where bitZero :: a' seems overkill to me.
However, "bit (-1)"[1] seems to result in just such a zero-value for all 'Bits' instances from base, so I'd hereby propose to simply document this as an expected property of 'bit', as well as the recommended way to introduce a zero-value (for when 'Num' is not available).
Discussion period: 2 weeks
[1]: ...or more generally 'bit n == 0' for n<0, as it's usually implemented as 'bit n = 1 shift n' _______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries