On 23/03/2009 7:37 PM, Stavros Macrakis wrote:
Tested in R 2.8.1 Windows
ff <- formals(function(x)1)
ff1 <- as.list(function(x)1)[1]
# ff1 acts the same as ff in the examples below, but is a list rather
than a pairlist
dput( ff , control=c("warnIncomplete"))
list(x = )
This string is not parsable, but dput does not give a warning as specified.
That's not what "warnIncomplete" is documented to do. The docs (in
?.deparseOpts) say
'warnIncomplete' Some exotic objects such as environments,
external pointers, etc. can not be deparsed properly. This
option causes a warning to be issued if any of those may give
problems.
Also, the parser in R < 2.7.0 would only accept strings of up
to 8192 bytes, and this option gives a warning for longer
strings.
As far as I can see, none of those conditions apply here: ff is not one
of those exotic objects or a very long string. The really relevant
comment is in the dput documentation:
"Deparsing an object is difficult, and not always possible."
Yes, it would be nice if deparsing and parsing were mutual inverses, but
they're not, and are documented not to be.
dput( ff , control=c("all","warnIncomplete"))
list(x = quote())
This string is parseable, but quote() is not evaluable, and again dput
does not give a warning as specified.
In fact, I don't know how to write out ff$x.
I don't know of any input that will parse to it.
It appears to be the
zero-length name:
is.name(ff$x) => TRUE
as.character(ff$x) => ""
This may give you a hint:
> y <- ff$x
> y
Error: argument "y" is missing, with no default
It's a special internal thing that triggers the missing value error when
evaluated. It probably shouldn't be user visible at all.
Duncan Murdoch
but there is no obvious way to create such an object:
as.name("") => execution error
quote(``) => parse error
The above examples should either produce a parseable and evaluable
output (preferable), or give a warning.
-s
PS As a matter of comparative linguistics, many versions of Lisp allow
zero-length symbols/names. But R coerces strings to symbols/names in
a way that Lisp does not, so that might be an invitation to obscure
bugs in R where it is rarely problematic in Lisp.
PPS dput(pairlist(23),control="all") also gives the same output as
dput(list(23),control="all"), but as I understand it, pairlists will
become non-user-visible at some point.
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