[Rd] Inspect a "delayed" assigned whose value throws an error?
Martin Maechler
maechler at lynne.stat.math.ethz.ch
Tue Jan 27 15:56:19 CET 2015
>>>>> Henrik Bengtsson <hb at biostat.ucsf.edu>
>>>>> on Mon, 26 Jan 2015 12:41:48 -0800 writes:
> On Mon, Jan 26, 2015 at 12:24 PM, Hadley Wickham <h.wickham at gmail.com> wrote:
>> If it was any other environment than the global, you could use substitute:
>>
>> e <- new.env()
>> delayedAssign("foo", stop("Hey!"), assign.env = e)
>> substitute(foo, e)
>>
>> delayedAssign("foo", stop("Hey!"))
>> substitute(foo)
> Hmm... interesting and odd.
> Unfortunately, this doesn't seem to help for reaching into the
> namespace of hgu133a.db and inspecting 'hgu133aPFAM', e.g.
>> library("hgu133a.db")
>> substitute(hgu133aPFAM, env=ns)
> Error: hgu133aPFAM is defunct. Please use select() if you need access to PFAM
> or PROSITE accessions.
>> evalq(substitute(hgu133aPFAM), envir=ns)
> Error: hgu133aPFAM is defunct. Please use select() if you need access to PFAM
> or PROSITE accessions.
>> evalq(substitute(hgu133aPFAM, env=ns), envir=ns)
> Error: hgu133aPFAM is defunct. Please use select() if you need access to PFAM
> or PROSITE accessions.
this *is* interesting..
Note that shortly after delayedAssign() was introduced into R,
we had
R : Copyright 2005, The R Foundation for Statistical Computing
Version 2.2.1 (2005-12-20 r36812)
ISBN 3-900051-07-0
............
> delayedAssign("x", pi^2) ; substitute(x)
pi^2
>
so it also worked with the globalenv; but that feature already
disappeared with
R : Copyright 2006, The R Foundation for Statistical Computing
Version 2.3.0 (2006-04-24)
Almost surely as an inadvertent side effect of something else.
-----------------------------------
--> Quiz (even though it's not Friday) :
The help page for delayedAssign() contains a somewhat more
sophisticated example of 'promise's, and BTW an example that
worked also in *much* earlier version of R, probably in all
versions of R {I checked R 1.0.1, probably the oldest still
running on my current Linux desktop} :
e <- (function(x, y = 1, z) environment())(1+2, "y", {cat(" HO! "); pi+2})
which gives an environment full of promises
Now, the following also works alread in R 1.0.1 :
> gete <- function(e)
lapply(lapply(ls(env=e), as.name),
function(n) eval(substitute(substitute(X, e), list(X=n))))
> gete(e)
[[1]]
1 + 2
[[2]]
[1] "y"
[[3]]
{
cat(" HO! ")
pi + 2
}
>
In newer versions of R, you can use 'ls(e)' instead of
'ls(env=e)', and we have bquote() to make it a tad shorter:
gete2 <- function(e)
lapply(lapply(ls(e), as.name), function(n) eval(bquote(substitute(.(n), e))))
Apart from that (and from not using spaces and from silly things
such as 'L = lapply', and using L),
can anyone find a shorter (or "nicer") way to achieve the same
as gete(), or gete2(), i.e., return a list with the promise expressions and
not evaluating e ?
You are not allowed to use 'x', 'y', and 'z' explicitly of
course, because here,
gete0 <- function(e) list(substitute(x,e), substitute(y,e), substitute(z,e))
would be slightly shorter.
Martin
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