OpenEuphoria

RE: How to tell the difference bewteen comparing and assigning

• Posted by Derek Parnell <ddparnell at bigpond.com> May 13, 2002
• 519 views

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.