Java Reference
In-Depth Information
/
Visitor code for Marker
18
on page 302
/
procedure
visit
(StructDefining
structde f
)
typeRe f
←
new
TypeDescriptor(
structType
)
typeRe f
.
fields
←
39
new
SymbolTable()
foreach
decl
∈
structde f
.
fieldList
do
40
call
decl
.
f ieldType
.
accept(
this
)
foreach
id
∈
vld
.
idList
do
41
if
typeRe f
.
fields
.
declaredLocally(
id
.
name
)
then
call
42
error
(”
Name cannot be redeclared
:”
,
id
.
name
)
id
.
type
←
errorType
id
.
attributesRe f
←
null
else
attr
.
kind
←
f ieldAttributes
attr
.
f ieldType
←
decl
.
f ieldType
.
type
call
typeRe f
.
fields
.
enterSymbol(
id
.
name
,
attr
)
id
.
type
←
decl
.
f ieldType
.
type
id
.
attributesRe f
←
attr
43
structde f
.
type
←
typeRe f
44
end
Figure 8.22:
visit
method in TypeVisitor for StructDefining.
outer loop, the TypeVisitor is propagated to the AST representing the type
specification for one set of fields. Within the inner loop, each field identifier is
checked for previous declaration within the struct (at Marker
42
). Presuming
that it passes this test, beginning at Marker
43
,aFieldAttriburesrepresentation
is created for the name, which is then entered into the symbol table for the
struct. The
method finishes at Marker
44
by leaving a reference to the
completed TypeDescriptor for the struct type within the StructDefining node
that represents it in the AST.
visit
An enumeration type is defined by a list of distinct identifiers. Each identifier
is a constant of the enumeration type. These constants are ordered by their
position in the type definition and are represented internally by integer values.
Typically, the value used to represent the first identifier is zero, and the value
for each subsequent identifier is one more than that for its predecessor in the
list (although Ada does allow a programmer to specify the values used to
represent enumeration literals). If runtime error checking is enabled, then the
value zero might be used to represent ”uninitialized,” with valid enumeration
values begining at one. An abstract syntax tree for an enumeration type
definition is shown in Figure 8.24.
