Variables

Local variables are created with the let statement. Variable types are determined at runtime and include numbers, strings, and tables. In its simplest form, the let statement specifies the name of the variable and an expression for its value as in:

let $message = "Hello " + $requester;

Object Values

However, the let statement may also have more complex destructuring left-hand sides. Although variables cannot be objects, there are several places in Paraflow where object values may appear, and the destructuring let statement enables those objects to be unpacked into scalar local variables.

One common place objects appear is in the response to a skill request. Skill requests that return data almost always return an object. Here’s an example of a weather skill that returns current conditions as an object:

task !FetchWeather($ts) is
  pncp let {
    $humidity,
    temperature_c: $temp,
    wind: {
      speed_km_hr: $wind_speed,
      direction: $wind_dir
    }
  } = weather/current in {
    insert weather($ts, $humidity, $temp, $wind_speed, $wind_dir);
  }

The destructuring left-hand side describes how a possibly nested object is mapped to local variables. Each desired field of the source object has a binding that specifies where to store its value. For example, the response object in this example has a field named temperature_c, and the binding indicates that the field's value should be assigned to the local variable $temp. The $humidity reference is just shorthand for humidity: $humidity. The wind field is a nested object, so its binding is an object that binds its fields to variables.

If this skill were to return the response:

{
  "humidity": 67,
  "temperature_c": 18,
  "wind": {
    "speed_km_hr": 12,
    "Direction": "NNE"
  }
}

Then the local variables would be:

Variable	Value
$humidity	67
$temp	18
$wind_speed	12
$wind_dir	NNE

Table Values

Local variables may also contain tables. See the Local tables section for a detailed description of local table variables.

Constants

Constants can be defined at the file-level and may be referenced anywhere in events, rules and tasks. Constants are defined as follows:

constant $MAX_N = 37;

Uppercase names are commonly used to help distinguish them as constants in the code.