RE: How to tell the difference bewteen comparing and assigning
Chris Bensler wrote:
>
> irv at take.maxleft.com wrote:
> >
> > jbrown105 at speedymail.org wrote:
> > > On 0, stabmaster_ at HOTMAIL.COM wrote:
> > > >
> > > > One way to spot comparisons (although it probably doesn't cover _all_
> > > > possible comparisons) are when '=' is used after 'if' or 'while'
> > > >
> > > > if 1=0 then...
> > > >
> > > > while 0=1 do...
> > > >
> > > > etc.
> >
> > Why don't you download Dave Cuny's Py interpreter
> > and see how he did it?
> > IIRC it uses = as both an assignment operator and
> > a comparison operator. For atoms AND sequences.
> >
> > Regards,
> > Irv
>
> AFAIK, Py is a complete language, which parses and processes every token
>
> of code.
>
> I'm pretty sure James is trying to avoid doing that.
>
> My preprocessor also parses and processes every token of code. I don't
> see any other way of being able to accurately determine if = is an
> assignment or operator.
You can't. The token '=' must be semantically checked in context. If the
token is immediately preceded by an identifer-reference AND that
references a variable AND that identifier is at the beginning of a
statement, then the '=' is an assignment, othewrwise is is a equality
comparision.
It is unfortunate that RDS choose '=' to mean two different things
depending on where it is placed in the source code, but Euphoria is not
alone in that regard.
As an aside, I've often thought that '?=' is a good token for equality
comparision and ':=' for assignment - but I'm probably out numbered 
--------
Derek.
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