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From: abcscnuk@csuna.csun.edu (Naoto Kimura)
Newsgroups: comp.lang.pascal
Subject: Reusing identifiers (was (re:)**3 function return value)
Summary: Keep in mind the scope
Message-ID: <1765@csuna.csun.edu>
Date: 16 Mar 89 10:52:25 GMT
References: <18654@adm.brl.mil> <134300005@cdp>
Reply-To: abcscnuk@csuna.csun.edu (Naoto Kimura)
Organization: CSU Northridge
Lines: 97
Keywords:

In article <134300005@cdp> ipis@cdp.UUCP writes:
>
>I see no reason why it shouldn't be legal.  Are you concerned with the
>multiple declarations of "D" and "T" (no problem because they're inside
>records) or of using a user-defined type in a record?  Either one
>should be fine.
>--andy

There IS a problem.  Suppose we have the following program:

    1	program foo(input,output);
    2	type
    3	    X	= 0..7;
    4	    Y	= record
    5		X : integer;
    6		Z : X
    7		end;
    8	    T	= record
    9		Z : X;
   10		X : integer;
   11		end;
   12	    Z	= X;
   13	begin
   14	end.

at line 3	"X" is defined to be a subrange 0..7
at line 5	Within the scope of the record type "Y", "X" is now a
		field of type integer.   We can reuse the identifier "X"
		because we are not in the same scope as the previous
		definition.
at line 6	We encounter a problem -- "X" isn't a type but is a
		field.
at line 9	We encounter the same problem as we did on line 6
at line 12	We can use "X" as a type, since within the scope of
		the program it is a type.


Believe it or not, the following program really is a legal pascal
program.  I originally wrote it to experiment with scoping of
identifiers.  It should help illustrate the scoping rules.

    1	program pathological (output);
    2	const
    3	   writeln =  1;
    4	   readln  = 50;
    5	type
    6	   real    = writeln..readln;
    7	   write   = (eof, eoln);
    8	   read    = char;
    9	   boolean = packed array [ real ] of read;
   10	var
   11	   get     : read;
   12	   true,
   13	   false   : write;
   14	   dispose : boolean;
   15	
   16	procedure maxint  ( var eoln : text;
   17	                        get  : boolean;
   18	                        eof,
   19	                        read : real     );
   20	   forward;
   21	
   22	procedure integer  ( var eof   : text;
   23	                         get   : boolean;
   24	                         read,
   25	                         write : real    );
   26	   begin
   27	      if read < write then begin
   28	         maxint ( eof, get, write, read+1 );
   29	         eof^ := get[read];
   30	         put (eof);
   31	      end;
   32	   end;
   33	
   34	procedure maxint;
   35	   begin
   36	      if read < eof then begin
   37	         integer ( eoln, get, read, eof-1 );
   38	         eoln^ := get[eof];
   39	         put (eoln);
   40	      end;
   41	   end;
   42	
   43	begin
   44	   true  := eof;
   45	   false := eof;
   46	   dispose := '     .ri rvgitmsso agr iT hspormde oehn eywed     ';
   47	   if true = false then begin
   48	      integer ( output, dispose, writeln, readln );
   49	   end;
   50	end.

                //-n-\\			 Naoto Kimura
        _____---=======---_____		 (abcscnuk@csuna.csun.edu)
    ====____\   /.. ..\   /____====
  //         ---\__O__/---         \\	Enterprise... Surrender or we'll
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