meemoo app: test equation in port

gistfile1.txt

{
  "info": {
    "author": "meemoo",
    "title": "equation evaluation in port",
    "description": "Meemoo app description",
    "parents": [],
    "url": "test-equation"
  },
  "nodes": [
    {
      "id": 0,
      "src": "meemoo:ui/vslider",
      "x": 120,
      "y": 162,
      "w": 108,
      "h": 208,
      "state": {
        "value": 0.5,
        "min": 0,
        "max": 1,
        "step": 0
      }
    },
    {
      "id": 1,
      "src": "meemoo:image/circle",
      "x": 413,
      "y": 141,
      "w": 200,
      "h": 210,
      "state": {
        "x": 50,
        "y": 50,
        "r": "=50*x",
        "fill": "black",
        "strokewidth": 1
      }
    }
  ],
  "edges": [
    {
      "source": [
        0,
        "value"
      ],
      "target": [
        1,
        "r"
      ]
    }
  ]
}