Several years ago, Anders Hejlsberg (chief designer of C#) and Peter Golde thought of extending C# to better integrate data querying. Peter, who was the C# compiler development lead at the time, was investigating the possibility of making the C# compiler extensible, specifically to support add-ins that could verify the syntax of domain-specific languages like SQL. Anders, on the other hand, was conceiving a deeper, more specific level of integration. He was thinking about a set of “sequence operators” that would operate on any collection that implemented IEnumerable, as well as remote queries for types that implemented IQueryable.

At this point one could argue that the CGFunction API allows you to create any of the function types because you can code up the function however you want. While this does work in an interactive environment, once you print you are exclusively in the realm of sampled functions as the PDF generation can not magically turn your C function into a PDF function definition other than sampled.