RDF.Literal.datatype-question-mark

You're seeing just the function datatype-question-mark, go back to RDF.Literal module for more information.

Returns if the given value is a RDF.Literal or RDF.Literal.Datatype struct.

If you simply want to check for a RDF.Literal use pattern matching or RDF.literal?/1. This function is a bit slower than those and most of the time only needed when implementing RDF.Literal.Datatypes where you have to deal with the raw, i.e. unwrapped RDF.Literal.Datatype structs.