let sub := (docs.toSubarray 0 docs.size.pred).toArray
    let middle := sub.map (fun d => Doc.Concat d sep)
    let inner := Doc.group (middle.push last) ""
    Doc.groupIndent #[(0, l), (indent, inner), (0, r)] ""

    let all_but_last := (docs.toSubarray 0 docs.size.pred).toArray
    let withSeps := all_but_last.map (fun d => (indent, Doc.Concat d sep))
    let contents := #[(0, l)] ++ withSeps ++ #[(indent, last), (0, r)]
    Doc.groupIndent contents ""