Libmarpa handling of semantics is unusual. Most semantics are left up to the application, but Libmarpa guides them. Specifically, the application is expected to maintain the evaluation stack. Libmarpa’s valuator provides instructions on how to handle the stack. Libmarpa’s stack handling instructions are called “steps”. For example, a Libmarpa step might tell the application that the value of a token needs to go into a certain stack position. Or a Libmarpa step might tell the application that a rule is to be evaluated. For rule evalution, Libmarpa will tell the application where the operands are to be found, and where the result must go.
The detailed discussion of Libmarpa’s handling of semantics is in the reference chapters of this document, under the appropriate methods and classes. The most extensive discussion of the semantics is in the section that deals with the methods of the value time class. See Value methods.