Concepts of Programming Languages

458 Chapter 10 Implementing Subprograms

is no visible scope containing a declaration for the variable D, so this reference

to D is a static semantics error. The error would be detected when the compiler

attempted to compute the chain_offset / local_offset pair. The reference to E is

to the local E in Sub2, which can be accessed with the pair (0, 5).

In summary, the references to the variable A at points 1, 2, and 3 would be

represented by the following points:

• (0, 3) (local)


• (2, 3) (two levels away)


• (1, 3) (one level away)

Figure 10.9

Stack contents at
position 1 in the
program Main_2

ARI = activation record instance

B

Local

Local

Parameter

Dynamic link

Static link

ARI for

Sub2

X

E

B

A

X

C

C

Local E

Local

Dynamic link

Static link

Return (to Sub2)

ARI for

Sub3

A

D

Top

Local

Local

Local

Dynamic link

Static link

Return (to Main_2)

Local

ARI for

Bigsub

ARI for

Main_2

Return (to Bigsub)

Local

Local

Dynamic link

Static link

Return (to Sub3)

ARI for

Sub1