Semantic Analysis - Crafting a Compiler - page 370

Trying
catches

tryBody final

StmtList StmtList

. . .

. . .

Catching

Figure 9.24: Abstract Syntax Tree for a Try Statement

Catching

catchIdDecl catchBody more

StmtList . . .

CatchIdDeclaring

type Catching

ident

Figure 9.25: Abstract Syntax Tree for a Catch Block

finally statements are analyzed. Semantic analysis of the catch clauses is
defined at Marker 30 .
Catch clauses require careful analysis. Each clause introduces a new iden-
tifier, the parameter of the clause. This identifier must be declared as an
exception (of class Throwable or a subclass of it). The parameter is made local
to the body of the catch clause by opening, and later closing, a new name
scope.
Using method , defined in Figure 9.27, we verify

that the current catch clause does not ”hide” later catches. This is a reachability
issue—some exception type must be able to reach, and activate, each of the
catch clauses in a try statement.
Throws analysis for try statements is defined in Figure 9.28 at Marker 32 .
Catch clauses and finally statements are visited to collect the exceptions they
might throw. Before the try body is analyzed, we must include the exception
types declared in the try's catch clauses. We maintain a ”catch list” containing
all exception types potentially handled by enclosing try blocks. At the start
of analysis for a method or constructor, this list is null. Assume the method
get

subsumes L ater C atches

gives us the current catch list. Before updating the catch list
to include exceptions in the current catch clauses, we save the current catch
list into currentCatchList .Thecallto

C atch L ist

adds exceptions in the
current catch clauses to the catch list. Now the try body can be analyzed.
After its analysis, the catch list is restored using

update C atch L ist

set C atch L ist .Oncewe