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From: DMB@PSUVMA.BITNET
Newsgroups: net.lang
Subject: Discussion on removing punctuation in programming languages
Message-ID: <7796DMB@PSUVMA>
Date: Wed, 8-Oct-86 15:55:07 EDT
Article-I.D.: PSUVMA.7796DMB
Posted: Wed Oct  8 15:55:07 1986
Date-Received: Fri, 10-Oct-86 00:43:50 EDT
Expires: Mon, 17-Nov-86 00:00:00 EDT
Lines: 105


    Punctuation or seperators (; , .) have long been a part of programming
language design. Anyone who has programmed for even the shortest amount of
will realize that these little demons are responsible for a large amount of
possible errors, thus the question is why have them at all?

   The obvious answer is not for the programmer, but for the compiler writer
and his compiler. This is true for at least two reasons.
   One, the seperator (usually a parse list seperator (, or ;) signals the
the parser that another item is following which should be included in the
list (i.e. repeat while next symbol is a seperator) instead of having to
repeat until you reach an end of list symbol.
   Second, error recovery is easily done for instance in Pascal's ; because
on an error, the parser can go into panic mode until it sees a ; at which
time it can assume that things are pretty stable and continue parsing again.

   The question is, are these or any other reasons valid enough to keep these
 gremlins in the programming language specifications. Maybe so, i assume not.

   What is it that we really want by using seperators
      1) When a parse unit begins and ends
      2) ???????

   By a parse unit i mean such things as statements, blocks, declarations,etc.
   How do we know when a unit ends and the next begins? Until now we used the
   seperator.

   I consider Wirth's Modula-2 an attempt to take a step away from all this
   seperator nonsense. However, he choose not to do so, as the semicolon is
   still prevalently used.

   I propose we can remove the semicolon, without losing its effectiveness
   by insisting that statements (and in general parse units) be equally
   bracketed. By this I mean that every construct have some sort of
   end-construct at the end of the construct. In Modula-2, for instance,
   the for statement is for id := expr to expr <seqstmt> END.  And similarly
   if's, case's repeats,whiles all have end "brackets". Thus any two of these
   compounds when butted up against each other, the beginning and end of each
   statement can be found even if one of the middle symbols is missing.
   (missing symbols meaning, the ending symbol of the first compound statement
    or the beginning symbol of the second compound statement). This is
    exactly what the semicolon was used for. Ah but there is a problem, the
    assignment statement! consider the statements a := b + c   e := f + g
    Without a seperator, you don't know if the e is part of the first statement
    (missing operator) or part of the second statement, UNTIL you read the
    second :=.  Thus I will require an end of assignment statement token to be
    introduced, (notice a weakness in my proposal here). But the assignment
    statement is the only case where this is needed.

    Is this arguement clear? Correct?

Example program with proposed syntax.

Program Dummy

Const
   (v p x) = 5
Type
   thetype = array[0 5] of integer
Var
   (x1 x2 x3 x4 x5):integer
   (y1 y2 y3 y4 y5):real

Procedure proc1(var (x3 x2):integer)
begin
   x1 := x3 + x2 END
   for x1 := 1 to x5 do
      x4 := 1 div x1 END
      while x4 < 10 do
          x4 := 1 + x4
      end
   end
end

begin
   x3 = 0
   repeat
      proc1(x3,x5)
   until x3 > x5 end
end


Don't try to analyse this program, it does nothing at best.

Admittedly, this looks an awful lot like swapping ; for end, and that is
probably so. But aren't end's alot more intuitive then ; ? Maybe not, maybe
so. Which is better? That's up to you.. What do you think?








As a side note does any language allow the mathematically normal syntax of
   IF (4 < x < 8) THEN blabla

I don't think so, but why not?




                                      dave brosius
                                      dmb at psuvma.bitnet