From ripley@stats.ox.ac.uk  Fri Jan  4 13:51:29 2002
From: ripley@stats.ox.ac.uk (ripley@stats.ox.ac.uk)
Date: Fri, 4 Jan 2002 14:51:29 +0100 (MET)
Subject: [Rd] Problem with "missing" in "local" (PR#1241)
Message-ID: <200201041351.OAA07843@pubhealth.ku.dk>

On Fri, 4 Jan 2002 J.C.Rougier@durham.ac.uk wrote:

> Hi everyone,
>
> I encountered unexpected behaviour when calling "missing" within a
> "local" environment, namely
>
> fred <- function(x, y)
> {
>   x <- as.vector(x)
>   local({
>     dontwantme <- 1:100
>     if (missing(y)) print("No \"y\" today")
>   })
>   x
> }
>
> whereupon I get
>
> > fred(1:10)
> Error in eval(expr, envir, enclos) : "missing" illegal use of missing
>
> I think it is reasonable to expect missing to work in this context (I
> suspect the problem relates to lazy evaluation): if not, it might be
> helpful to amend the help file.

Why do you think it reasonable?  You've take a function from

     Evaluate an R expression in a specified environment.

and evaluated it somewhere where missing() is not defined.  If you had
used eval() explicitly, would you think it reasonable?  I doubt it.

Which help file did you have in mind?

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-devel-request@stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._


[Rd] Problem with "missing" in "local" (PR#1241)
ripley@stats.ox.ac.uk