As in Ada, suppose that each expression must have a unique type, but that from a subexpression, by itself, all we can deduce is a set of possible types. That is, the application of function Ei to...

As in Ada, suppose that each expression must have a unique type, but that from a subexpression, by itself, all we can deduce is a set of possible types. That is, the application of function Ei to argument E2 , represented by E —> Ei (Ei), has the associated rule


E.type = {t \ for some s in E2 .type, s ->• t is in Ei.type }


Describe an SDD that determines a unique type for each subexpression by using an attribute type to synthesize a set of possible types bottom-up, and, once the unique type of the overall expression is determined, proceeds top-down to determine attribute unique for the type of each subexpression.