The Haskell 2010 report defines, in chapter 9, round :: (Real a, Fractional a, Integral b) => a -> b round x = let (n, r) = properFraction x -- n = truncate x, r = x-n (same sign as x) m = if r < 0 then n - 1 else n + 1 in case signum (abs r - 0.5) of -1 -> n -- round in if |r| < 0.5 1 -> m -- round out if |r| > 0.5 0 -> if even n then n else m (commented and slightly rearranged). The traditional definition of rounding to integer, so traditional that it is actually given in the OED, is basically round x = truncate (x + signum x * 0.5) There was a discussion of rounding recently in another mailing list and I put together this table: * Round x.5 OUT Ada, Algol W, C, COBOL, Fortran, Matlab, Pascal, PL/I, Python, Quintus Prolog, Smalltalk. The pre-computing tradition. * Round x.5 to EVEN Common Lisp, R, Haskell, SML, F#, Wolfram Language. * Round x.5 UP to positive infinity Java, JavaScript, ISO Prolog, Algol 60 * Rounding of x.5 UNSPECIFIED Algol 68, IMP 77 What I was wondering was whether anyone on this list knew why Haskell has the break-ties-to-even definition instead of the traditional break-ties-out one. (And please don't say that it is to get statistical unbiasedness, because given the kinds of data distribution I see, it _isn't_ unbiased.)