I lost some time trying to figure out why I got



Copy pasting or using // Hold // FullForm showed what the problem is

RowBox[{"f", "[", "]"}],

The lefthand side was copy-pasted from somewhere (probably a message) where it was displayed in HoldForm.

I would like such expressions to look differently.

In version 11 we finally got different styling of Initialization cells (gray background), not just a tiny "I" in the cell brace. Inactivated expressions also display differently. But HoldForm are visually indistinguishable from regular input.

Can I do something to change the formatting of HoldForm expressions? Which Format rules or stylesheets do I have to change to get this?

  • $\begingroup$ Somewhat related: (56715) $\endgroup$
    – Mr.Wizard
    Aug 30 '16 at 12:19

I'm using this now:

   StandardForm] := {boxes = MakeBoxes@x, bg = LightBlue}~With~
     TagBox[StyleBox[boxes, Background -> bg], "", 
      Selectable -> False], HoldForm[x]];

The TagBox stops you from selecting anything inside the expression.

This makes the result clearer:

enter image description here

Another variant would be to just make HoldForm display directly like Hold, but the visual clutter might be unacceptable to you:

Format[HoldForm[x_], StandardForm] := 
  RawBoxes@TagBox[RowBox@{"HoldForm", "[", MakeBoxes@x, "]"}, "", 
    Selectable -> False];

(I left out the InterpretationBox here - TODO)

For reference, this is what HoldForm does by default:

Format[HoldForm[x_], StandardForm] := 
  RawBoxes@TagBox[MakeBoxes@x, HoldForm];

Nice idea. Your original construct did not play well with ReleaseHold though; here is one that should:

MakeBoxes[x_HoldForm, StandardForm] :=
  Block[{$holdstyle = True},
      Style[x, Background -> LightBlue, StripOnInput -> False, Selectable -> False],
    ] // ToBoxes
  ] /; ! TrueQ[$holdstyle]
  • 1
    $\begingroup$ Thanks, I fixed a problem with ReleaseHold in the current version. $\endgroup$
    – masterxilo
    Aug 30 '16 at 12:17
  • $\begingroup$ @masterxilo So I see. I guess then I'll emphasize the ability to use Style rather than StyleBox etc., making writing this just a little easier. $\endgroup$
    – Mr.Wizard
    Aug 30 '16 at 12:19
  • $\begingroup$ I did not think of catching nested HoldForm, I guess your version will perform better in such cases. $\endgroup$
    – masterxilo
    Aug 30 '16 at 12:19

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