Class Code Examples

First Example
This is a simple procedure call in which the parameters are computed
and stored in locations local to the procedure call
1 var 
2 	x,y; 
3 procedure p(x,u); 
4 var 
5 	t; 
6 	t:= x+u; 
7 begin 
8 	x:= 1; 
9 	y:=2; 
10 	p(2*x+1,y) 
11 end. 
Compile successful...no errors!

Object code for this program is 
step    fun    lev    add
   0    jmp      0      8
   1    jmp      0      2
   2    int      0      6
   3    lod      0      3
   4    lod      0      4
   5    opr      0      2
   6    sto      0      5
   7    opr      0      0
   8    int      0      5
   9    lit      0      1
  10    sto      0      3
  11    lit      0      2
Compute the parameter values and store in local stack area
  12    sto      0      4
  13    inb      0      0
  14    int      0      5
  15    lit      0      2
  16    lod      1      3
  17    opr      0      4
  18    lit      0      1
  19    opr      0      2
  20    sto      0      3
  21    lod      1      4
  22    sto      0      4
  23    deb      0      0
  24    cal      0      2
  25    opr      0      0


After step number 0


After step number 8

Base-> 1         0
       2         0
       3         0
       4         0
 Top-> 5         0

After step number 9

Base-> 1         0
       2         0
       3         0
       4         0
       5         0
 Top-> 6         1

After step number 10

1
Base-> 1         0
       2         0
       3         0
       4         1
 Top-> 5         0

After step number 11

Base-> 1         0
       2         0
       3         0
       4         1
       5         0
 Top-> 6         2

After step number 12

2
Base-> 1         0
       2         0
       3         0
       4         1
 Top-> 5         2

After step number 13

       1         0
       2         0
       3         0
       4         1
 Top-> 5         2
*****************************************************
During the run
****************************************************
After step number 14

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8         0
       9         0
 Top-> 10         0

After step number 15

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8         0
       9         0
       10         0
 Top-> 11         2

After step number 16

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8         0
       9         0
       10         0
       11         2
 Top-> 12         1

After step number 17

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8         0
       9         0
       10         0
 Top-> 11         2

After step number 18

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8         0
       9         0
       10         0
       11         2
 Top-> 12         1

After step number 19

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8         0
       9         0
       10         0
 Top-> 11         3

After step number 20

3
       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8         0
       9         3
 Top-> 10         0

After step number 21

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8         0
       9         3
       10         0
 Top-> 11         2

After step number 22

2
       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8         0
       9         3
 Top-> 10         2

After step number 23

Base-> 1         0
       2         0
       3         0
       4         1
 Top-> 5         2

After step number 24

       1         0
       2         0
       3         0
       4         1
 Top-> 5         2

After step number 2

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8        25
       9         3
       10         2
 Top-> 11         2

After step number 3

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8        25
       9         3
       10         2
       11         2
 Top-> 12         3

After step number 4

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8        25
       9         3
       10         2
       11         2
       12         3
 Top-> 13         2

After step number 5

       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8        25
       9         3
       10         2
       11         2
 Top-> 12         5

After step number 6

5
       1         0
       2         0
       3         0
       4         1
       5         2
Base-> 6         1
       7         1
       8        25
       9         3
       10         2
 Top-> 11         5

After step number 7

Base-> 1         0
       2         0
       3         0
       4         1
 Top-> 5         2

After step number 25

Second Example
This example shows how the dynamic and static links are created for nested
procedures.

1 var 
2 	x, y; 
3 procedure p(u,x); 
4 	var 
5 		w; 
6 procedure p1(); 
7 	x:=u + w +y; 
8 procedure p2(); 
9 	p1(); 
10 	p2(); 
11 p(1,2). 
Compile successful...no errors!

Object code for this program is 
step    fun    lev    add
   0    jmp      0     18
   1    jmp      0     15
   2    jmp      0      3
   3    int      0      3
 

  
4    lod      1      3


   5    lod      1      5
   6    opr      0      2
   7    lod      2      4
   8    opr      0      2
   9    sto      1      4
  10    opr      0      0
  11    jmp      0     12
  12    int      0      3
  13    cal      1      3
  14    opr      0      0
  15    int      0      6
  16    cal      0     12
  17    opr      0      0
  18    int      0      5
  19    inb      0      0
  20    int      0      5
  21    lit      0      1
  22    sto      0      3
  23    lit      0      2
  24    sto      0      4
  25    deb      0      0
  26    cal      0     15
  27    opr      0      0


After step number 0


After step number 18

Base-> 1         0
       2         0
       3         0
       4         0
 Top-> 5         0

After step number 19

       1         0
       2         0
       3         0
       4         0
 Top-> 5         0

After step number 20

       1         0
       2         0
       3         0
       4         0
       5         0
Base-> 6         1
       7         1
       8         0
       9         0
 Top-> 10         0

After step number 21

       1         0
       2         0
       3         0
       4         0
       5         0
Base-> 6         1
       7         1
       8         0
       9         0
       10         0
 Top-> 11         1

After step number 22

1
       1         0
       2         0
       3         0
       4         0
       5         0
Base-> 6         1
       7         1
       8         0
       9         1
 Top-> 10         0

After step number 23

       1         0
       2         0
       3         0
       4         0
       5         0
Base-> 6         1
       7         1
       8         0
       9         1
       10         0
 Top-> 11         2

After step number 24

2
       1         0
       2         0
       3         0
       4         0
       5         0
Base-> 6         1
       7         1
       8         0
       9         1
 Top-> 10         2

After step number 25

Base-> 1         0
       2         0
       3         0
       4         0
 Top-> 5         0

After step number 26

       1         0
       2         0
       3         0
       4         0
 Top-> 5         0

After step number 15

       1         0
       2         0
       3         0
       4         0
       5         0
Base-> 6         1
       7         1
       8        27
       9         1
       10         2
 Top-> 11         2

After step number 16

       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         2
 Top-> 11         2

After step number 12

       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         2
       11         2
Base-> 12         6
       13         6
 Top-> 14        17

After step number 13

       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         2
       11         2
       12         6
       13         6
 Top-> 14        17

After step number 3

       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         2
       11         2
       12         6
       13         6
       14        17
Base-> 15         6
       16        12
 Top-> 17        14

After step number 4

       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         2
       11         2
       12         6
       13         6
       14        17
Base-> 15         6
       16        12
       17        14
 Top-> 18         1

After step number 5

       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         2
       11         2
       12         6
       13         6
       14        17
Base-> 15         6
       16        12
       17        14
       18         1
 Top-> 19         2

After step number 6

       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         2
       11         2
       12         6
       13         6
       14        17
Base-> 15         6
       16        12
       17        14
 Top-> 18         3

After step number 7

       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         2
       11         2
       12         6
       13         6
       14        17
Base-> 15         6
       16        12
       17        14
       18         3
 Top-> 19         0

After step number 8

       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         2
       11         2
       12         6
       13         6
       14        17
Base-> 15         6
       16        12
       17        14
 Top-> 18         3

After step number 9

3
       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         3
       11         2
       12         6
       13         6
       14        17
Base-> 15         6
       16        12
 Top-> 17        14

After step number 10

       1         0
       2         0
       3         0
       4         0
       5         0
       6         1
       7         1
       8        27
       9         1
       10         3
       11         2
Base-> 12         6
       13         6
 Top-> 14        17

After step number 14

       1         0
       2         0
       3         0
       4         0
       5         0
Base-> 6         1
       7         1
       8        27
       9         1
       10         3
 Top-> 11         2

After step number 17

Base-> 1         0
       2         0
       3         0
       4         0
 Top-> 5         0

After step number 27