HW4 -- Due 6/04/97

1) Consider the following program written in a ALGOL-like language:

procedure BLAH;
  integer GLOBAL;
  integer array LIST[1:2];
  procedure FOO (PARAM);
    integer PARAM;
    begin
      PARAM := 3;
      GLOBAL := GLOBAL + 1;
      PARAM := 5
    end;
  begin
    LIST[1] := 3;
    LIST[2] := 1;
    GLOBAL := 1;
    FOO (LIST(GLOBAL))
  end;

Hand execute the program under the following assumptions, and compare
the resulting values in the array LIST in BLAH after the return from
FOO.

a) Parameters are passed by value.
b) Parameters are passed by reference.
b) Parameters are passed by name.
b) Parameters are passed by value-result.


2) FORTRAN allows a subprogram to have multiple entry points.  Why is
this sometimes a valuable capability ?

3) Show the stack with all activation record instances, including
static and dynamic chains, when execution reaches position 1 in the
following skeletal program:


procedure BLAH;
  procedure A;
    procedure B;
      begin {B}
      ...               <------------ 1
      end; {B}
    procedure C;
      begin {C}
      ...
        B;
      ...
      end; {C}
    begin {A}
    ...
    C;
    ...
    end; {A}
  begin {BLAH}
  ...
  A;
  ...
  end; {BLAH}


4) For the skeletal program in Problem 3, show the display that would
be active at position 1, along with the activation records on the
stack.

5) Show the stack with all activation record instances, including
static and dynamic chains, when execution reaches position 1 in the
following skeletal program:


procedure BLAH;
  procedure C; forward;
  procedure A (FLAG : boolean);
    procedure B;
      begin {B}
      ...
      A (false)
      end; {B}
    begin {A}
      if FLAG
        then B
        else C
    ...
    end; {A}
    procedure C;
      procedure D;
        begin  {D}
        ...            <--------------- 1
        end;   {D}
      begin {C}
      ...
        D;
      ...
      end; {C}
  begin {BLAH}
  ...
  A(true);
  ...
  end; {BLAH}

The calling sequence for this program for execution to reach D is

   BLAH calls A
   A calls B
   B calls A
   A calls C
   C calls D

Show the local variables as part of the activation.