OpenEuphoria

Re: Rob, no reply? Minor bug found in 3.1 and previous

• Posted by Robert Craig <rds at RapidEuphoria?com> Jul 07, 2007
• 564 views

I don't plan to do anything about this.
It's a rare situation, and I don't think it's 
worth the trouble to try to improve the error message.

Al Getz wrote:
> 
> Al Getz wrote:
> > 
> > Robert Craig wrote:
> > > 
> > > Al Getz wrote:
> > > > 
> > > > --program:
> > > > constant x=1
> > > > x=2
> > > > --end program
> > > > 
> > > > --error message:
> > > > C:\Euphoria\Projects\Test\test.exw:2
> > > > x has not been declared
> > > > x=2
> > > > ^
> > > > 
> > > > Press Enter
> > > > --end message
> > > > 
> > > > 
> > > > Error message should be "May not change the value of a constant",
> > > > or something like that.
> > > 
> > > Yes, that would be a better message.
> > > You've caught the parser and scanner at an awkward moment.
> > > What's happening here is that you're making the scanner
> > > look up x in the symbol table, when the parser hasn't quite
> > > finished the constant declaration of x. The fact that
> > > you enter a new-line character after constant x = 1
> > > is no more significant than typing a blank, and
> > > the parser needs to see the next scanner token to be sure that
> > > the constant declaration is really finished. You might have
> > > had:
> > > }}}
<eucode>
> > >     constant x = 1
> > >     + 1  -- x is 2
> > > </eucode>
{{{

> > > for instance. Until the parser digests the next token after " = 1",
> > > it can't be sure that the declaration is finished,
> > > and can't record that x is a constant with value 1
> > > in the symbol table.
> > > 
> > > Regards,
> > >    Rob Craig
> > >    Rapid Deployment Software
> > >    <a href="http://www.RapidEuphoria.com">http://www.RapidEuphoria.com</a>
> > 
> > 
> > Hi Rob,
> > 
> > 
> > Ok, but it looks to me like logically it is not too hard to detect
> > the end of a constant declaration.  Whether or not the parser can
> > do this yet or not i dont know, apparently it can not.
> > 
> > I think i see what you are talking about however, in that the
> > following program gives the same error:
> > 
> > --
> > constant y=2
> > constant x=y x=1
> > --
> > 
> > Apparently though something sees the whitespace and is able to terminate the
> > "x=y" part once the 'x' is encountered, it is just not able to understand
> > the difference
> > between a comma or whitespace or other, non-variable-starter characters
> > (which would tell it to keep parsing the constant declaration) and
> > an actual variable-starter character.
> > In other words, if it encounters a character that is in the set of
> > all characters that can be a variable starter then it is forced to
> > terminate the constant declaration.  Isnt the current set A to Z and
> > a to z ?  Note there is no possibilty of:
> > 
> >   constant x=y x  --(which would trigger an "x is not declared" error)
> > 
> > where the user intended
> > 
> >   constant x=yx
> > 
> > 
> > and also
> > 
> >   constant x=x
> > 
> > would probably trigger an "x is not declared" error (referring to
> > the second x).
> > 
> > 
> > Make sense or did i assume too much?
> > 
> > 
> > Bottom line is that the main reason i mentioned this is because
> > when you get the error message "x is not declared" it makes you
> > think you can go somewhere near the beginning of the program and
> > type "atom x" and all will be fine 
> > Only after typing that will the real problem show itself (x was
> > already declared as a constant) on the next run.
> > 
> > 
> > Al

Regards,
   Rob Craig
   Rapid Deployment Software
   http://www.RapidEuphoria.com