Abstract

MACHINE: REWRITING SEMANTICS The rewriting semantics is defined by the tables below representing possible transitions from left columns to right columns. The global data structure is a multiset of tasks together with a function (set of pairs) mapping syntactic nodes of the term being evaluated to tables. There are two main forms of tasks. The first component of tasks is the name of a cell together with the term whose type contains it. The last component of tasks is always a mode: either a value computed for the given cell, a failure marker ? to indicate that the cell could not be filled, or a request mode. A simple request mode "?" simply means a general request to fill the cell. An indexed request mode ? c means a request with the added information that the value sought is also that of cell c. As an example of this last kind of mode, see rule CL2 in the first table. A last kind of mode ? tr indicates that a slice of state (A(x) in the operational semantics) is currently being filled....

Citations