I need a convenient interface to interactively explore very large expressions. I am aware of Short and Shallow, and appreciate the front-end feature that allows to show a large expression in initially concise and gradually expandable form, with placeholders for collapsed expressions. I would like something similar to this, but with some additional features. In particular, I would like to be able to both expand and collapse sub-expressions, view a summary of a collapsed sub-expression in its tooltip (Head, Length, Depth, LeafCount — ideally, customizable), and have a way to copy a sub-expression to the clipboard. Is there anything similar to this?

  • $\begingroup$ One particular scenario where I could use it is large expression simplification. Sometimes FullSimplify cannot make much progress in a reasonable time, but I found that if I manually identify sub-expressions that seems "simplifiable" and apply FullSimplify specifically to them, then I can often achieve significant simplification much faster. $\endgroup$ – Vladimir Reshetnikov Sep 4 '19 at 22:45
  • 1
    $\begingroup$ maybe something like expr1= RandomInteger[5,{2,2}]; expr2=Partition[{a,b,c,d},2]; labels= {"expr 1","expr 2"}; fview =FlipView[{ Tooltip[Iconize[#,#2],Grid@#],#}]&; MapThread[fview,{{expr1,expr2}, labels}]? $\endgroup$ – kglr Sep 5 '19 at 4:38

The following code does what I think you want:

  1. Right clicking converts the selected portion into a button with a ».
  2. Clicking on the » expands the button back into the selected portion.
  3. The "HotKeys" option allows you to define rules so that a hot key will apply a desired function on the selected portion.
  4. The tooltip that is created can be customized by modifying the $ExpandableInformation global variable.

Here is an animation of the code in action:

enter image description here

You will see expressions collapsed when right-clicking, and simplified when using the "F" key.

One issue is that quitting the kernel will disable the form.

Here is the code:

Options[ExpandableForm] = {"HotKeys" -> {}};

ExpandableForm /: MakeBoxes[ExpandableForm[expr_, OptionsPattern[]], StandardForm] := With[
    events = 
        {"MouseClicked", 2} :> NotebookApply[
        ], (* right clicking collapses the selected expression *)
        Sequence @@ addEvents[OptionValue[ExpandableForm, "HotKeys"]]
        (* process "HotKeys" options *)
    With[{boxes = MakeBoxes[expr, StandardForm]},
            (* setup EventHandler *)
            TagBox[boxes, EventHandlerTag[events]],
            DisplayFunction -> (#1&),
            InterpretationFunction -> (#2&)

(* make ExpandableForm a wrapper *)
	$OutputForms = DeleteDuplicates @ Append[$OutputForms, ExpandableForm];

(* code to process and implement hot keys *)

addEvents[key_Rule] := addEvents[{key}]
addEvents[keys:{___Rule}] := Replace[
    Rule[key_, f_] :> key :> applyFunctionToSelection[f],

applyFunctionToSelection[f_] := Module[{expr},
    expr = ToExpression[NotebookRead[SelectedNotebook[]], StandardForm, Hold];
    If[MatchQ[expr, _Hold],
        Replace[expr, Hold[a_] :> ToBoxes@f[a]]

(* code to collapse boxes *)
collapsedBoxes[boxes_] := TemplateBox[
    {"»", boxes},
    DisplayFunction -> (ButtonBox[
        ButtonFunction :> NotebookWrite[ParentBox @ EvaluationBox[], #2, All],
        Evaluator -> Automatic
    InterpretationFunction -> (#2&),
    Tooltip -> ToBoxes @ boxInfo[boxes]

(* gather expression information *)
boxInfo[boxes_] := Quiet[
        ToExpression[boxes, StandardForm, expressionInfo],

SetAttributes[expressionInfo, HoldAll];

expressionInfo[expr_] := Grid[
        (label_ -> h_) :> {Row[{label,":"}], h[Unevaluated @ expr]},
    Alignment -> {{Right, Left}, Baseline}

(* customizable global variable to control what the tooltip shows *)

$ExpandableInformation = {
    "Head" -> Head,
    "Length" -> Length,
    "Depth" -> Depth,
    "LeafCount" -> LeafCount
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