On Sun, Jun 28, 2009 at 15:24, Andrew Coppin<andrewcop...@btinternet.com> wrote: > I just wrote a small module for dealing with half-integers. (That is, any > number I/2 where I is an integer. Note that the set of integers is a subset > of this; Wikipedia seems to reserve "half-integer" for such numbers that are > *not* integers.) > > module HalfInteger where > > data HalfInteger i > > instance (Eq i) => Eq (HalfInteger i) > instance (Ord i) => Ord (HalfInteger i) > instance (Integral i) => Show (HalfInteger i) > instance (Integral i) => Num (HalfInteger i) > > half :: (Num i) => HalfInteger i > > fromNum :: (Integral i, RealFrac x) => x -> HalfInteger i > toNum :: (Integral i, Fractional x) => HalfInteger i -> x > > isInteger :: (Integral i) => HalfInteger i -> Bool > > Note carefully that the set of half-integers is *not* closed under > multiplication! This means that for certain arguments, there are two > reasonable products that could be returned. (E.g., 1/2 * 1/2 = 1/4, so 0 or > 1/2 would be a reasonable rounding.) I haven't put a lot of effort into the > rounding details of (*) or fromNum; which answer you get is kind of > arbitrary. (However, addition and subtraction are exact, and for > multiplications where an exact result is possible, you will get that > result.) > > The Show instance outputs strings such as > > fromInteger 5 > fromInteger 5 + half > fromInteger (-5) - half > > depending on the isInteger predicate. > > Now, the question is... Is this useful enough to be worth putting on > Hackage?
Out of curiosity, what are *you* using it for? Thomas _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe