Spring COP4020 2011 Homework Assignment 7
1.
Consider the following pseudo-code program:
sum : integer // a global variable
procedure add(amount : integer)
sum := sum + amount
procedure p(x : integer, adder : procedure)
integer sum
sum := x
adder(x) // invoke procedure that was passed as argument
write_integer(sum)
begin // main program
sum := 0
p(1, add)
end
a.
Suppose dynamic scoping with shallow binding is used by the interpreter
to execute this code. What is the value printed by the program?
b.
Suppose dynamic scoping with deep binding is used by the interpreter to
execute this code. What is the value static printed?
c.
2.
Suppose scoping is used. What is the value printed by the program?
What is the value printed by the following pseudo-code program for each of the
four parameter passing modes call-by-value, call-by-reference, call-byvalue/result, and call-by-name? That is, for each of the four parameter passing
modes assume that both the x and y parameters use that mode. Show how each
program is evaluated in that mode and show the final value printed:
a : integer // a global variable
procedure p(x : integer, y : integer)
x := x + 1
a := y
begin // main program
a := 2
p(a, a)
write_integer(a)
end