Programming Language Qualifiers Examination Spring, 2001

Question 1:

Coroutine A Coroutine B Coroutine C

if ( )

resume B resume C

// address = 1000; // address = 2000; resume A

// address = 3000;

if ( )

resume C

// address = 4000;

Return address 1000

2000

3000

4000

In the above example, each time when a resume ID is called, traditional imperative

Language will first memorizing the return address and then go to the address of the

Returned address of that coroutine.

Assumption: Dynamically determine the returned address in the run time for

Each coroutine.

Question 2:

For above example,

Compiler can staticly determine an array of pointer, such as

Code *return[3];

And then the above codes were compiled as follows:

return[0] = &A;

return[1] = &B;

return[2] = &C;

Code *cp, *temp;

// Resume B

temp = cp;

cp = return[1];

return[0] = temp;

goto cp;

// Resume C

temp = cp;

cp = return[2];

return[1] = temp;

goto cp;

// Resume A

temp = cp;

cp = return[0];

return[2] = temp;

goto cp;

// Resume C

temp = cp;

cp = return[2];

return[0] = temp;

goto cp;

Question 3

Intuitively we may need to modify the “store” definition.

From

Store : Location à Denotable_Value

To

Store: Id à Value, where

Value = Nat + ( Command à Store à Store )