Semantic Analysis - Crafting a Compiler - page 358

procedure (Continuing cn )

currentList ← get

visit

L abel L ist ()

if cn . stmtLabel = null

then
while currentList null do

currentLabel ← head ( currentList )

if currentLabel . kind = iterative
then return
currentList ← tail

( currentList )

call error (” Continue not inside iterative statement ”)

else
while currentList null do

currentLabel ← head

( currentList )
if currentLabel . label = cn . stmtLabel and currentLabel . kind = iterative
then return
currentList ← tail

( currentList )

call error (” Continue label doesnot match an iterative statement ”)

end

Figure 9.12: Semantic Analysis for a Continue

the AST of the labeled statement). Looking at a label list, we can determine the
statements that enclose a break or continue, as well as all of the labels currently
visible to the break or continue.
The semantic analysis visitor for a LabeledStmt is shown in Figure 9.11.
The current label list is extendedby adding an entry for the current LabeledStmt
node using its label (which may be null), and its kind (determined by a call to
an auxiliary method, ). The subtree is analyzed using the extended

label list. After semantic analysis, the label list is returned to its original state
by removing its first element. Reachability and throws analyses are defined at
Figure 9.3, Marker 7 and Figure 9.4, Marker 14 .
A continue statement without a label references the innermost iterative
statement (while, do, or for) within which it is nested. This is easily checked
by looking for a node on the label list with kind = iterative (ignoring the value
of the label field).
Acontinue statement that references a label L (stored inASTfield stmtLabel )
must be enclosed by an iterative statement whose label is L . If more than one
containing statement is labeled with L , the nearest (innermost) is used. The
semantic analysis visitor for a continue statement is shown in Figure 9.12.
Reachability and throws analyses for a continue are defined at Figure 9.3,
Marker 8 and Figure 9.4, Marker 15 .
As an example, consider the following code fragment:

get K ind