Concepts of Programming Languages

452 Chapter 10 Implementing Subprograms

main. The others have a return address to the function itself; these are for

the recursive calls.

Figure 10.8 shows the stack contents for the three times that execution

reaches position 2 in the function factorial. Position 2 is meant to be the

time after the return is executed but before the activation record has been

removed from the stack. Recall that the code for the function multiplies

the current value of the parameter n by the value returned by the recursive

call to the function. The first return from factorial returns the value 1.

The activation record instance for that activation has a value of 1 for its ver-

sion of the parameter n. The result from that multiplication, 1, is returned

to the second activation of factorial to be multiplied by its parameter

value for n, which is 2. This step returns the value 2 to the first activation

Figure 10.7

Stack contents at position 1 in factorial

ARI = activation record instance

Top

Functional value

Parameter

Dynamic link

Return (to main)

Local

First ARI
for factorial

ARI

for main

3 n

?

? value

n

Functional value

Parameter

Dynamic link

Return (to main)

Local

First ARI
for factorial

ARI

for main

3

?

?

n

Top

Functional value

Parameter

Dynamic link

Return (to factorial)

Second ARI
for factorial

2

?

value

n

Functional value

Parameter

Dynamic link

Return (to main)

Local

First ARI

for factorial

ARI

for main

3

?

?

n

Functional value

Parameter

Dynamic link

R eturn (to factorial)

Second ARI

for factorial

2

?

n

Top

value

Functional value

Parameter

Dynamic link

R eturn (to factorial)

Third ARI

for factorial

1

?

First call

Second call

Third call