(this was inspired by libfive, antimony and Ronin)
EDIT: see a Proof-of-Concept demonstration and explanation video here.
an electronics CAD software could have a livecoding typing area somewhere, here illustrated with some Clojure pseudocode: (I chose a lisp-y thing because originally I thought that was going to be relevant, but now I see it is not at all necessary. Which is good news because it means this could be built more easily on top of the KiCAD API as it is, potentially.)
(let [rect (select-rect)
footprints (sort by-name (select-footprints))
min-stride (max (map footprints (fn [fp] (width fp))))
cols (floor (/ (width rect) min-stride))]
rows (ceil (/ (count footprints) cols))]
(each [[column x] (enumerate (group-into-bins cols footprints))]
(each [[footprint y] (enumerate column)]
(let [pos (+ (origin rect) (* (size rect) (vec2 (/ x cols) (/ y rows))))]
(move-to footprint pos)))))
...but you don't have to hit enter or a button to make it execute, and you don't have to undo if it didn't do what you wanted it to. The code is continuously parsed and interpeted as it is edited (as long as it is valid). The API used isolates all application state behind a non-mutable API, that runs like an immediate mode UI library:
select-rectdraws a rectangle that can be selected, moved, resized and returns its current origin and size vecctorsselect-footprintshighlights selected footprints, lets you shift-click to add/remove footprints from the set, and returns the current setmove-topreviews the destination positions
The function-invocations register themselves with the editor UI, which draws these visualisations and keeps state for them as long as the editing session exists and the function invocation is not removed.
This lets the user tweak the code and make sure it works, as well as tweak the selections etc.
Once the user is happy with the result, they can commit the changes.
To commit the changes, the API is switched into a different mode, where the select-* functions simply
return the last known state, while the move-to function applies the change instead of previewing it.
With this mode-changed API the block is executed one final time, and the changes are recorded into an undo-redo step.