What is EvaluatorValueLogic ?

An object implementing EvaluatorValueLogic interface is called before evaluation. This object transforms leaf values in the abstract syntax tree.

Why to use an EvaluatorValueLogic ?

The object lets you to enable custom pre-treatments on JSON in Json-Logic-Typed format.

Imagine you need to share common JSON in Json-Logic-Typed format between several components (frontend/backend/data). You also need to elaborate a custom pre-treatment specific to each of these components.

Example

Let’s suppose you receive JSON in Json-Logic-Typed format. One of the leaf nodes (in the syntax tree) is a string representing a car as: brand + vehicle registration number.

Imagine that all your defined logic and operators needs be applied on only the vehicle registration number.

EvaluatorValueLogic is all you need to handle this for you. For example, evaluation could be performed not on the previous expression (syntax tree) but the following one.

How to define a custom EvaluatorValueLogic ?

A custom object that implements EvaluatorValueLogic is defined by the Type that it is associated to.

Example: In the previous example, the associated Type with the EvaluatorValueLogic implementation object would be {"codename": "string"}.

EvaluatorLogicConf defines how Types are mapped with EvaluatorValueLogic. To use, pass EvaluatorLogicConf as an init parameter to EvaluatorLogic.

In the EvaluatorLogicConf object, information is contained through the parameters valueLogicTypeToReducerMetaInfAdd and valueLogicTypeToReducerManualAdd. They are mappings of Type to EvaluatorValueLogic.

You need to pass only your EvaluatorValueLogic mapping object to the EvaluatorLogicConf.createConf method.

val myStringEvaluatorValueLogic = ...
val valueLogicTypeToReducerManualAdd = Map(SimpleTypeValue("string") -> myStringEvaluatorValueLogic)
implicit val confEvaluator = EvaluatorLogicConf.createConf(valueLogicTypeToReducerManualAdd=valueLogicTypeToReducerManualAdd)
val evaluator = new EvaluatorLogic
evaluator.eval(...)

How to implement a custom operator ?

Implementing the EvaluatorValueLogic trait only requires to implement `` method.

Example: Based on the previous example

object CustomEvaluatorValueLogic extends EvaluatorValueLogic {
  def evaluateValueLogic(value: Any): Any = {
    value match {
      case string: String => ...
      case _ => throw ...
    }
  }
}

val valueLogicTypeToReducerManualAdd = Map(SimpleTypeValue("string") -> CustomEvaluatorValueLogic)
implicit val confEvaluator = EvaluatorLogicConf.createConf(valueLogicTypeToReducerManualAdd=valueLogicTypeToReducerManualAdd)
val evaluator = new EvaluatorLogic
evaluator.eval(...)

Define an EvaluatorValueLogic: as a service

Please refer to Advanced: Define custom object as Java Services