{
  "name": "Scoped params",
  "description": "Params are named subexpressions: define once in the set's (global) or a rule's (local) 'params', reference anywhere in that scope as { \"param\": \"name\" }. A local name shadows a global one. References are inlined at load, so params never change what a rule computes - only how it reads.",
  "params": {
    "averageItem": {
      "op": "divide",
      "operands": [ { "field": "Order.Total" }, { "field": "Order.ItemCount" } ]
    },
    "rate": 0.1
  },
  "rules": [
    {
      "id": "pricey-basket",
      "description": "The global 'averageItem' param used as a condition's computed left-hand side.",
      "condition": {
        "expression": { "param": "averageItem" },
        "operator": "GreaterThan",
        "value": 25
      },
      "actions": [
        { "type": "setOutput", "target": "PriceyBasket", "value": true },
        { "type": "setOutput", "target": "AverageItemPrice", "value": { "param": "averageItem" } }
      ]
    },
    {
      "id": "standard-discount",
      "description": "The global 'rate' param inside a computed action value.",
      "condition": { "field": "Order.Total", "operator": "GreaterThanOrEqual", "value": 100 },
      "actions": [
        {
          "type": "setOutput",
          "target": "Discount",
          "value": { "op": "multiply", "operands": [ { "field": "Order.Total" }, { "param": "rate" } ] }
        }
      ]
    },
    {
      "id": "vip-discount",
      "description": "A local 'rate' shadows the global one for this rule only.",
      "params": { "rate": 0.2 },
      "condition": { "field": "Customer.IsVip", "operator": "Equals", "value": true },
      "actions": [
        {
          "type": "setOutput",
          "target": "VipDiscount",
          "value": { "op": "multiply", "operands": [ { "field": "Order.Total" }, { "param": "rate" } ] }
        }
      ]
    }
  ]
}