Java Reference
In-Depth Information
procedure
visit
(Assigning
n
)
call
C
ode
G
en
(
n
.
child
2)
call
E
mit
( "s" )
call
E
mit
(
n
.
child
1
.
id
)
call
E
mit
( "0 k" )
14
end
procedure
visit
(Computing
n
)
call
C
ode
G
en
(
n
.
child
1)
call
C
ode
G
en
(
n
.
child
2)
call
E
mit
(
n
.
operation
)
15
end
procedure
visit
(SymReferencing
n
)
call
E
mit
( "l" )
call
E
mit
(
n
.
id
)
end
procedure
visit
(
Printing
n
)
call
E
mit
( "l" )
call
E
mit
(
n
.
id
)
call
E
mit
( "p" )
call
E
mit
( "si" )
16
end
procedure
visit
(Converting
n
)
call
C
ode
G
en
(
n
.
child
)
call
E
mit
( "5 k" )
17
end
procedure
visit
(Consting
n
)
call
E
mit
(
n
.
val
)
end
Figure 2.14: Code generation for ac
• visit
(Printing
n
)istrickybecausedc does not discard the value on top-
of-stack after it is printed. The instruction sequence si is generated at
Marker
16
, thereby popping the stack and storing the value in dc's i
register. Conveniently, the ac language precludes a program from using
this register because the i token is reserved for spelling the terminal
symbol integer.
• visit
(Converting
n
) causes a change of type from integer to float at
Marker
17
. This is accomplished by setting dc's precision to five frac-
tional decimal digits.
Figure 2.15 shows how code is generated for the AST shown in Figure 2.9.
Each section shows the code generated for a particular subtree of Figure 2.9.
