Funciton/Digital root calculator

This is a Funciton program that outputs the digital root of an input number. The input is expected to be an integer (not followed by a newline or any other whitespace).

I wrote this before I realised there is the efficient formula `1+(n-1)%9`. The program could be a lot smaller if that formula were used. Nevertheless, this demonstrates recursion in Funciton as well as some library functions such as `÷%` (division and modulo).

```                        ╓───╖
║ ‰ ║
╙─┬─╜
┌──────────┴────────┐
┌────────┴────────┐    ┌─────┴────┐
│                 │  ┌─┴─╖        │        ╔════════════════════════════════╗
│                 │  │ − ║        │        ║  digital root                  ║
│                 │  ╘═╤═╝        │        ╟────────────────────────────────╢
│  ╔════╗  ┌───╖  │  ┌─┴─╖        │        ║  If ↓ < 0, negate              ║
│  ║ 10 ╟──┤ < ╟──┘  │ ‰ ║        │        ║  If ↓ < 10, answer is ↓        ║
│  ╚════╝  ╘═╤═╝     ╘═╤═╝    ┌───┴───┐    ║  Else call ‰p and then repeat  ║
│          ┌─┴─╖     ┌─┴─╖  ┌─┴─╖     │    ╚════════════════════════════════╝
└──────────┤ ? ╟─────┤ ? ╟──┤ > ║     │
╘═╤═╝     ╘═╤═╝  ╘═╤═╝     │
┌─┴─╖       │    ╔═╧═╗     │
│ ‰ ║            ║ 0 ║     │            ╔═══╗
╘═╤═╝            ╚═══╝     │            ║   ║
╔═══╗  ┌─┴──╖                     │            ╚═╤═╝
║ 0 ╟──┤ ‰p ╟─────────────────────┘            ┌─┴─╖
╚═══╝  ╘════╝                                  │ 《 ║
╘═╤═╝
┌───────────────────────────┐                ┌─┴─╖
│     ╓┬───╖                │                │ ‰ ║
├─────╫┘‰p ╟──┐             │                ╘═╤═╝
│     ╙────╜  │             │                ┌─┴─╖
│     ╔════╗  │             │                │ 》 ║
│     ║ 10 ║  │             │                ╘═╤═╝
│     ╚═╤══╝  │             │                  │
│     ┌─┴──╖  │             │
│  ┌──┤ ÷% ╟──┴────────┐    │
│  │  ╘═╤══╝           │    │    ╔═════════════════════════════╗
│  │    └───────┐      │    │    ║  digital root (helper)      ║
│  │  ┌────╖  ┌─┴─╖    │    │    ╟─────────────────────────────╢
│  └──┤ ‰p ╟──┤ + ║    │    │    ║  → is an accumulator        ║
│     ╘═╤══╝  ╘═╤═╝  ┌─┴─╖  │    ║  If → = 0, result is ←      ║
│       │       └────┤ · ╟──┘    ║  Else, add last digit of →  ║
│     ┌─┴─╖          ╘═╤═╝       ║  to ← and recurse           ║
└─────┤ ? ╟────────────┘         ╚═════════════════════════════╝
╘═╤═╝
│
```