. INFERENCE
Semantic processing in compilers and other language processors, such as data flow analysis, can frequently be specified as in a rule-based, logical deductive style. In Prop, deductive inference using forward chaining7 is provided as a built-in mechanism, orthogonal to pattern matching and rewriting, for manipulating user-defined algebraic datatypes.
Similar to syntax classes, inference classes may be used
for data encapsulation. An inference class is a combination of a C++
class, a database of inference relations, and a collection of inference rules
of the form lhs -> rhs. The lhs of an inference rule is a set
of patterns in conjunctive form. During the inference process, a rule is
fired when its lhs condition is satisfied. A fired rule then executes
the corresponding rhs action, which may assert or retract additional relations
from the database. Using multiple inheritance, it is possible to combine
a rewriting class with an inference class such that the rewriting process
generates new relations to drive the inference process, or vice versa.