R devel - Nov 2008 - assign("FALSE", TRUE)

It was recently pointed out by Wacek Kusnierczyk that although one is
prevented from doing

	FALSE <- TRUE

one *can* do

	assign("FALSE",TRUE)

and have an object named ``FALSE'' with value TRUE in one's
workspace.

This apparently has no deleterious effects; e.g. doing

	sample(1:7,replace=FALSE)

gives a random permutation of 1:7 as expected and desired.  I.e. the
local object named ``FALSE'' is not used.

Still, this seems counterintuitive and a bit confusing.  Is it the  
intended
state of affairs?  I would have thought that

	FALSE <- <whatever>

and

	assign("FALSE",<whatever>)

would be completely equivalent.

This is clearly not a very important issue, but it might bear some  
thinking about.

	cheers,

		Rolf Turner

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>>>>> "RT" == Rolf Turner <r.turner at
auckland.ac.nz>
>>>>>     on Tue, 18 Nov 2008 08:49:21 +1300 writes:
    RT> It was recently pointed out by Wacek Kusnierczyk that
    RT> although one is prevented from doing

    RT> 	FALSE <- TRUE

    RT> one *can* do

    RT> 	assign("FALSE",TRUE)

    RT> and have an object named ``FALSE'' with value TRUE in
    RT> one's workspace.

    RT> This apparently has no deleterious effects; e.g. doing

    RT> 	sample(1:7,replace=FALSE)

    RT> gives a random permutation of 1:7 as expected and
    RT> desired.  I.e. the local object named ``FALSE'' is not
    RT> used.

    RT> Still, this seems counterintuitive and a bit confusing.
    RT> Is it the intended state of affairs?  I would have
    RT> thought that

    RT> 	FALSE <- <whatever>

    RT> and

    RT> 	assign("FALSE",<whatever>)

    RT> would be completely equivalent.

Yes, such thoughts are understandable but wrong as you now know.
Clearly
	assign("a b c", "abc")
does work, but
        a b c <- "abc"
does not; only 
        `a b c` <- "abc"
does, as well as
        `FALSE` <- TRUE

.... and Wacek did mention the backticks.
But in spite of all that I agree that I'd have liked
    `FALSE` <-  <whatever>
to signal an error about the fact that it is a reserved word.

    RT> This is clearly not a very important issue, but it might
    RT> bear some thinking about.

Yes.  I'd propose that R-core look into how to make assignment to a
reserved word an error.

Thank you, Rolf,
Martin

Rolf Turner wrote:
> 
> It was recently pointed out by Wacek Kusnierczyk that although one is
> prevented from doing
> 
>     FALSE <- TRUE
> 
> one *can* do
> 
>     assign("FALSE",TRUE)
> 
> and have an object named ``FALSE'' with value TRUE in one's
workspace.
> 
> This apparently has no deleterious effects; e.g. doing
> 
>     sample(1:7,replace=FALSE)
> 
> gives a random permutation of 1:7 as expected and desired.  I.e. the
> local object named ``FALSE'' is not used.
> 
> Still, this seems counterintuitive and a bit confusing.  Is it the intended
> state of affairs?  I would have thought that
> 
>     FALSE <- <whatever>
> 
> and
> 
>     assign("FALSE",<whatever>)
> 
> would be completely equivalent.
No, FALSE is a _keyword_ representing the logical value.

 > e <- quote(`FALSE` & FALSE)
 > e[[2]]
`FALSE`
 > e[[3]]
[1] FALSE
 > mode(e[[3]])
[1] "logical"
 > mode(e[[2]])
[1] "name"

The thing that is equivalent to assign("FALSE",<whatever>) is
`FALSE`<-whatever.

There are a couple of other keywords: TRUE, if, else, for, while, 
repeat, next, break, function. Did I forget any?

The stuff you can do with FALSE isn't really any stranger than

 > `2` <- pi
 > 2+2
[1] 4

so that two and two remains four for any value of `2`. You can't do 
2<-pi anymore than you can do FALSE<-foo.

> 
> This is clearly not a very important issue, but it might bear some 
> thinking about.
-- 
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