Path: utzoo!attcan!uunet!husc6!uwvax!dogie!uwmcsd1!csd4.milw.wisc.edu!markh
From: markh@csd4.milw.wisc.edu (Mark William Hopkins)
Newsgroups: comp.lang.pascal
Subject: The gaping hole left by var parameters ...
Summary: Aliasing, side-effects
Message-ID: <5879@uwmcsd1.UUCP>
Date: 25 May 88 04:20:21 GMT
Sender: daemon@uwmcsd1.UUCP
Reply-To: markh@csd4.milw.wisc.edu (Mark William Hopkins)
Organization: University of Wisconsin-Milwaukee
Lines: 100

What's wrong with var parameters?
Try these out to see how they compile and run:
Enjoy ...

(1) ALIASING:
      procedure Alias1(var X, Y : integer);
      begin
	 X := X + 1; Y := X + 1
      end;

      ...

   begin
      A := 3; Alias1(A, A); writeln(A)
   end.

   You might say that the whole is more than the sum of its parts ...
--------------------------------------------------------------------------------
      procedure Alias2(X : integer; var Y : integer);
      begin
	 X := X + Y + 1; A := A + Y + 1
      end;

      ...

    begin
       A := 3; Alias2(A, A); writeln(A)
    end.
--------------------------------------------------------------------------------
(2) INSIDUOUS SIDE-EFFECTS:

     function Insiduous1(var X, Y : integer; Z : integer) : boolean;
     begin
	X := X + 1; Y := Y + X; Insiduous1 := (X <= Z)
     end;
 
     ...

   begin
      A := 0; B := 0; C := 5;
      while Insiduous1(A, B, C) do {nothing};
      writeln('The sum of the integers from 0 to ', C:1, ' is :', B)
   end.
--------------------------------------------------------------------------------
      function ForLoop(var I, Bound : integer) : boolean;
      begin
	 ForLoop := (I < Bound);
	 I := I + 1
      end;

      ...

    begin
       I := 0; while ForLoop(I, 3) do A[I] := 2*I;
       I := 0; while ForLoop(I, 3) do write(A[I]:1, ' ');
       writeln
    end.

Why even use a for loop with this dandy available?
--------------------------------------------------------------------------------
    function Insiduous2(var X : integer) : integer;
    var Dummy : integer;
    begin
       if X >= 0 then begin
	  writeln('The final result is :', X:1)
	  Insiduous2 := X
       end
       else begin
	  Dummy := X + Insiduous2(X + 1);
	  writeln('The intermediate result was :', Dummy);
	  Insiduous2 := Dummy
       end
    end;

   begin
      A := -10;
      writeln(Insiduous2(A))
   end.

   This illustrates that an entire program could effectively be executed in one
write statement.
--------------------------------------------------------------------------------
String processing in Pascal?!

     function String : char;
     const PERIOD = '.';
     begin
	write('This is an arbitrary string');
	String := PERIOD
     end

     ...

   begin
      writeln(String)
   end;

   The function declaration is effectively the same as the assignment:

               String := 'This is an arbitrary string.';