after.imp

rightmost_child: edits.?edit edit parent~ @ max;
fix rightmost_leaf: edits.?edit edit | edit rightmost_child rightmost_leaf @ max;
prev_sibling: edits.?edit edit parent parent~ .(?sibling edit > sibling) @ max;
prev: edits.?edit edit prev_sibling !! then edit prev_sibling rightmost_leaf else edit parent;
fix position: root, 0 | position ?edit ?pos edit prev~, pos + 1;
edits ?edit (edit position), edit, (edit character)

before.imp

let rightmost_child = edits (?edit . edit . 
  (max [edit ~parent])) in
let rightmost_leaf = 
  fix none (?[rightmost_leaf] .
    edits (?edit . edit . 
      (max [edit | (edit rightmost_leaf rightmost_child)])))) in
let prev_sibling = edits (?edit . edit
  (max [(edit parent ~parent) (?sibling . (when (edit > sibling) sibling))])) in
let prev = edits (?edit . edit .
  if !!(prev_sibling edit)
    ([prev_sibling edit] max rightmost_leaf)
    (edit parent)) in
let position = 
  fix none (?[position] .
    edits (?edit . edit .
      if !(edit parent) then 0 else
      (edit prev position) + 1)) in
edits (?edit .
  (edit position) . edit . (edit character))