behavior of =

[Luke Tierney]

On Fri, 8 Nov 2002, Tony Plate wrote:

> At 08:41 AM 11/8/2002 -0800, A.J. Rossini wrote:
> >[...]
> >The "<-" assignment operator is beautiful.  It's taken me over a
> >decade, but I have come to appreciate it.  It isn't common, and there
> >are fewer and fewer ex-APL'ers, but I think it's a great choice.
> >
> >The use of "=" for named arguments in a function call signature makes
> >sense, and the use of "==" for equality makes sense.
> >
> >But syntactical sugar should only be messed with if broken (and yes,
> >this may be one of the few points that I'd disagree with John; I wish
> >he'd never introduced "=" as a possible assignment).
> >
> >best,
> >-tony
> 
> Yup, the S-language does have 3 separate symbols available for 3 separate 
> functions ("=" for named arguments, "<-" for assignment, and "==" for 
> equality).  Like Tony Rossini, I'd rather that these did not 
> overlap.  Would it be possible to give parse() (and source()) an argument, 
> or allow a pragma in a file, that would disallow the use of "=" for 
> assignment?  (Since "=" was introduced as an assignment operator in S 
> implementations, I've been bitten by the bug of a "="/"==" typo a couple of 
> times, and have never seen any benefit from the change.)

You can at least make sure you get a run time error by redefining "="
something like

"="<-function(...) stop("'=' used for assignment--I don't like that")

Doing that now has the potential of messing up some packages you might
want to use.  R 1.7 should include a name space mechanism that will
let you do this privately within your packages so "=" is disabled for
you but not for other mackages.

luke

-- 
Luke Tierney
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
   Actuarial Science
241 Schaeffer Hall                  email:      luke@stat.uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu

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