On 21/09/2011, at 2:59 AM, Chris Smith wrote:
On Mon, 2011-09-19 at 22:09 -0700, Evan Laforge wrote:
Then I tried switching to a fixed point format, and discovered my mistake. Enum is supposed to enumerate every value between the two points, and the result is memory exhaustion.
% ghci Prelude> [1.0..2.0]::[Double] [1.0,2.0] (..) for Doubles is using (+1), not nextAfter, and is NOT enumerating every value between 1.0 and 2.0
import Ratio Prelude Ratio> [1%2..7%2] :: [Ratio Int] [1 % 2,3 % 2,5 % 2,7 % 2]
(..) for (Ratio a) is using (+1), and is NOT enumerating the infinitely many values between 1.5 and 3.5. Why should your fixed point format behave any differently?
I certainly hope not. Instead, perhaps the issue should be brought up with the fixed-point number library you're using, and they could fix their Enum instance to be more helpful.
So Chris Smith's response is absolutely right here; the problem is the fixed-point library implementing enumeration incompatibly with the built-in numeric types.