On 3/27/2013 12:16 PM, Henning Thielemann wrote:
On Wed, 27 Mar 2013, Jeff Shaw wrote:
On Wednesday, March 27, 2013 11:30:24 AM, Henning Thielemann wrote:
I don't think that an Integral instance is the right way to go, since it would imply the signature:
div :: CTime -> CTime -> CTime
and the quotient of two time values is not a time.
That is irrelevant.
It is highly relevant and certainly a major difference between Haskell and C. A time can be represented with any unit and with either integer or floating or fixed-point numbers. Actually, the integer can always be read as fixed-point number, since the unit is somehow arbitrary. The quotient of two time values is not a time value but a scalar value and it is good if Haskell alerts you when you mix them up.
The functionality you want is located in Data.Time.Clock. Foreign.C.Types is for working with C values, which do permit integer division on time_t when it happens to be an integer, which as far as Haskell is concerned, is always. Your argument can also be used to say that C values with the unit "grapheme" shouldn't be allowed division, either. However, they are. Do you think we should remove the Integral instance for CChar? What about the Bounded and Bits instances? Data.Char.Char only has Bounded. Furthermore, CTime is an instance of Num, which means that you can do multiplication on CTime values. Do you think we should remove that? After all, Time * Time is Time ^2, not Time. Jeff