$'main'
 \-[100](!e!)-\  
              |
/----(!x!)0---/
|
|   /--s--1--(a)---m---------\
|   |                        |
|   \                        |
|    \              /-[1000]-/
\--1i----(!a!)(a)0q<
 /                  \
/                   |
|                   |
\                   |
 >{~}q0(e)(!x!)a(x)-/
/
|
\-(x)o#

$ '~' (a -- b):
 \         /-(e)1s(!e!)#
 |   /-t-\ |
 |  /     \|
 \-<       |
    \     /|
     \-f-/ @