Q:

Vertical "fractions" with more than 2 parts

Standard FractionBox syntax allows only 2 arguments and creates 2-part fraction for numerator and denominator.
Is it possible to draw similar construction, but with more than 2 parts? Some sort of column with separators only between inner parts?
The following code
Column[{"x", 200, Integrate[Sin[x^2], x]}, Alignment -> Center, Dividers -> Center]

draws best what I found but it does dividers of similar length in entire column. I would like dividers to accommodate two adjacent parts only.

A:

Interesting question.  I don't have much experience with this sort of thing so I imagine there is a better way but this is what I could hack together at the moment:
frac[lst_List] := Column[
  Column /@ Partition[Riffle[lst, \[HorizontalLine]], 2, 2, -1, {}], 
  Alignment -> Center, Spacings -> 0]

{"x", 200, Integrate[Sin[x^2], x]} // frac

Here is another approach, probably closer to "correct":
frac2[lst_List] :=
  Style[Fold[FractionBox, #, {##2}], ScriptSizeMultipliers -> 1] & @@
    (ToBoxes@Style[#, ScriptSizeMultipliers -> 0.71] & /@ lst) // DisplayForm

{"x", 200, Integrate[Sin[x^2], x]} // frac2

I am assuming that you want expressions at any tier of the notation to be the same size.  If you are fine with them shrinking as they go up then a much simpler form can be used without Style and ScriptSizeMultipliers:
frac3[lst_List] :=
  Fold[FractionBox, #, {##2}] & @@ (ToBoxes /@ lst) // DisplayForm

{"x", 200, Integrate[Sin[x^2], x], Integrate[Sin[x^2], x]} // frac3

