Question

Consider the following pseudocode which uses dynamic scoping. What does the program print if the language uses shallow binding? What does it print with deep binding? x: integer//global procedure print_x write_integer (x) procedure first x:= x * 3 procedure second (F: procedure) x: integer x: = 5 F () print_x () x: = 7 second (first) print_x ()

Answer 1

Deep binding binds the environment at the time a procedure is passed as an argument.

Shallow binding binds the environment at the time a procedure is actually called.

When deep binding;

Sequence of execution is

• x=7
• Second(first)
  • x=5
  • First()
    • x=x*3
    • x=7*3 …(x is taken as global in deep binding)
    • x=21 ---(now globa x become 21)
  • Print_x()
    • x=5 is passed to print_x so it will print 5 <-----ANS
• Print_x()
  • x=21 is been passed to function so 21 will be printed <---ANS

So 5,21 will be printed

When shallow binding

Sequence of execution is

• x=7
• Second(first)
  • x=5
  • First()
    • x=x*3
    • x=5*3 … (travel in func call stack until value of x found)
    • x=15
  • Print_x()
    • x=15 will be printed ….<----ANS
• Print_x()
  • x=7 will be printed<---ANS ..as x=7 is last value of x in function call stack

So 15,7 will be printed