OpenEuphoria

Re: Minor bug found in 3.1 and previous

• Posted by Al Getz <Xaxo at ?ol.com> Jul 01, 2007
• 708 views

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.



Take care,
Al

E boa sorte com sua programacao Euphoria!


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