Module API.QuerySource

Commodity module to build a simple query and extract the output from the solution found by Elpi.

Example: "foo data Output" where data has type t (a is t Conversion.t) and Output has type v (b is a v Conversion.t) can be described as:

      let q : (v * unit) t = Query {
        predicate = "foo";
        arguments = D(a, data,
                    Q(b, "Output",
                    N))
      }

Then compile q can be used to obtain the compiled query such that the resulting solution has a fied output of type (v * unit). Example:

     Query.compile q |> Compile.link |> Execute.once |> function
       | Execute.Success { output } -> output
       | _ -> ...