From Objects to Functions

Running Queries on Functors

The goal is to have a function that takes a QueryRunner and returns a result of an arbitrary type T. However, to ensure that the QueryRunner is in the proper state when the function is called, we’ll execute it as a functional effect in a secure way. To achieve this, we’ll create a functor named ProjectionQuery that wraps a function of type (QueryRunner) -> T.

Using a functor offers several advantages. Firstly, it gives us control over when the query is executed. We only want to run the query when it’s correct, and at a minimum, we need to ensure that the projections are up-to-date. In the future, there may be additional checks that need to be performed. Functors allow us to separate the technical infrastructure concerns ...