有没有更简洁的方法来重写 F# function？

Question

Here is a function that converts a number to a string with the requested precision and a leading sign:

let formatValueSign (precision: decimal) (value: decimal) =
    let precisionString =
        match precision with
        | 0.1m      -> "{0:+#.0;-#.0; 0.0}"
        | 0.01m     -> "{0:+#.00;-#.00; 0.00}"
        | 0.001m    -> "{0:+#.000;-#.000; 0.000}"
        | 0.0001m   -> "{0:+#.0000;-#.0000; 0.0000}"
        | 0.00001m  -> "{0:+#.00000;-#.00000; 0.00000}"
        | 0.000001m -> "{0:+#.000000;-#.000000; 0.000000}"
        | _         -> "{0:+#0;-#0;0}"

    String.Format(precisionString, value)

The expected output has the sign in front of the number and the precision is represented by a decimal number, but it can also be passed as i where the precision is pown 0.1mi if it's more convenient.

Is there a way to make this more concise?

Answer 1

If I understand what you want correctly, I think something like this does essentially the same thing:

(Decimal.Round(value / precision) * precision).ToString()

And it also handles precision > 1, such as:

formatValueSign 100m -12345.6789m -> "-12300"

You can tweak the ToString() part to generate the leading + sign if you want. Personally, I would break this into two functions, though: One to generate a decimal with the correct precision, and a separate one that formats it to your liking.

Last thought: I would probably define the precision as an integer exponent (eg -2 instead of 0.01m ), because the current signature accepts precisions that aren't powers of 10. Better to make invalid values unrepresentable IMHO.

Answer 2

You could calculate the number of zeros in the format string using log10 and then generate the format string dynamically. The following does not correctly handle corner cases, but it works for the cases in the middle of your range:

let formatValueSign (precision: decimal) (value: decimal) =
  let places = int (log10 (float (1.0m/precision)))
  let zeros = String.replicate places "0"
  let precisionString = sprintf "{0:+#.%s;-#.%s; 0.%s}" zeros zeros zeros
  String.Format(precisionString, value)