How can I make a “working” repeating decimal representation of a rational number?

Question

I\'ve figured out how to display the repeating part of a repeating decimal using OverBar.

repeatingDecimal doesn\'t actually work as a repeating decimal

Answer 1

Here is a possible refactoring of your updated code. I think it works this time (fingers crossed). If you do not need the color highlighting, you can leave off ~Style~ and the rest of that line.

ClearAll[repeatingDecimal];

Format[repeatingDecimal[n_Integer | n_Real]] := n;

Format[repeatingDecimal[q_Rational]] :=
 Row[{IntegerPart@q, ".", RealDigits@FractionalPart@q}] /.
  {{ nr___Integer, r_List:{} }, pt_} :>
   Row@Join[
      "0" ~Table~ {-pt},
      {nr},
      If[r === {}, {}, {OverBar@Row@r}]
      ] ~Style~ If[r === {}, Blue, If[{nr} === {}, Red, Gray]]

repeatingDecimal /:
  (h : Plus | Times)[left___, repeatingDecimal[q_], right___] :=
    h[left, q, right];

I will leave this older version here for reference, but I am now making edits to the Question community wiki.