Xref: utzoo comp.os.vms:5894 comp.lang.pascal:856
Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!ncar!boulder!tramp!sanford
From: sanford@tramp.Colorado.EDU (SANFORD STEPHEN LEE)
Newsgroups: comp.os.vms,comp.lang.pascal
Subject: Re: Quoted string parameters in VAX Pascal?
Message-ID: <5787@sigi.Colorado.EDU>
Date: 2 May 88 22:02:38 GMT
References: <Apr.29.15.09.31.1988.23840@elbereth.rutgers.edu>
Sender: news@sigi.Colorado.EDU
Reply-To: sanford@tramp.Colorado.EDU (Steve Sanford Jr.)
Organization: University of Colorado, Boulder
Lines: 71
Summary: "String" Records

In his provocative and exciting article,
   elkins@elbereth.rutgers.edu (George Elkins) writes:
>
>Is there a way in VAX Pascal to define a procedure that will take
>a variable length quoted string as a parameter?  What I would like
>to do is imitate the variable length quoted string parameter behavior
>of the WRITE and WRITELN procedures, although this is not possible
>for user-written procedures in STANDARD Pascal.  I want the quoted
>string parameter to be within the argument list itself, as in the
>WRITELN procedure.  I am trying to avoid assigning the string to an
>arbitrarily long fixed-length packed array and passing the Pascal
>identifier for the array and the integer length of the string.
>
>Example of what I want to do:
>
>     foo('This is a string of any length');  {User-written procedure foo}
>  . . . 
>
>George Elkins

One possibility is to define your "string" as follows:
----------------------------------------------------------
     type stringptr: ^newstring;
          newstring: record
                      ch: char;
                      next: stringptr
                     end;
     var x: newstring;
----------------------------------------------------------
Then, work with the string using procedures.  For example:
----------------------------------------------------------
     function length (x: newstring): integer;
      begin
       if (x = nil)
       then length := 0
       else length := 1 + length (newstring^.next)
      end;

     procedure readin (var x: newstring);
      var temp: newstring;
            ch: char;
      begin
        x := nil; 
        read (ch);
        if (not (eoln)) then
         begin
           new (x); x^.ch := ch; x^.next := nil; temp := x;
           read (ch);
           while (not (eoln)) do
            begin
              new (temp^.next);
              temp := temp^.next;
              temp^.ch := ch; temp^.next := nil;
              read (ch)
            end;
         end;
      end;   (* readin *)
---------------------------------------------------------------------
{These procedures could probably be improved upon; the checks for (eoln) might
  be improperly placed.  Give me more time, I'll give you correct code. }

Obviously, the data structure isn't a static "string", but a linked list
of characters.  The procedures are a bit more complicated, but it gives you
the "variability" you desired; strings can be as short or as long as you 
want, and "foo (x)" will work with them regardless.
     Good luck.  If you want, e-mail me a request for more (correct) code;
I'm just a poor student, who will do ANYTHING to avoid studying for finals.
                                  **************************************** 
      ___                        * If you set your mind to it, you can do *
     /__ teve                    *   do anything.  Except ski through a   *
    ___/anford Jr.               *           revolving door.              *
                                  ***************** - some optimist ******