> maybe there?s a reason for it, but the discrepancy between the
> handling of `[` and `$` in deparsing seems odd to me:
>
> > substitute(a[1], list(a = quote(x * y)))
> x * y[1]
>
> > substitute(a$b, list(a = quote(x * y)))
> (x * y)$b
>
> The former is still executed in the right order (`*` first, then
> `[`), which is not what you?d expect looking at the deparse result.
This is one of a large number of bugs in the deparser and parser that
are fixed in the latest version of pqR (of 2015-09-14), as a result of
a complete rewrite of the parser and extensive revisions to the
deparser. As I communicated to this list, it would be reasonably easy
to incorporate the rewritten parser and deparser into R Core versions
of R. You can get more details from http://www.pqr-project.org/NEWS.txt
The portion of the bugs section in that NEWS file relevant to parsing
and deparsing is shown below:
o The new parser fixes bugs arising from the old parser's kludge to
handle semicolons, illustrated by the incorrect output seen
below:
> p<-parse()
?"abc;xyz"
Error in parse() : <stdin>:1:1: unexpected INCOMPLETE_STRING
1: "abc;
^
> p<-parse()
?8 #abc;xyz
Error in parse() : <stdin>:1:7: unexpected end of input
1: 8 #abc;
^
o Fixed deparsing of complex numbers, which were always deparsed as
the sum of a real and an imaginary part, even though the parser
can only produce complex numbers that are pure imaginary. For
example, the following output was produced before:
> deparse(quote(3*5i))
[1] "3 * (0+5i)"
This is now deparsed to "3 * 5i". This bug exists in all R Core
versions through at least R-3.2.2.
o Fixed a number of bugs in the deparser that are illustrated by
the following, which produce incorrect output as noted, in R Core
versions through at least R-3.2.2:
deparse(parse(text="`+`(a,b)[1]")[[1]])# Omits necessary
parens
deparse(quote(`[<-`(x,1)),control="S_compatible") #
unmatched " and '
deparse(parse(text="a = b <- c")[[1]]) # Puts in
unnecessary parens
deparse(parse(text="a+!b")[[1]]) # Puts in unnecessary
parens
deparse(parse(text="?lm")[[1]]) # Doesn't know
about ? operator
deparse(parse(text="a:=b")[[1]]) # Doesn't know
about := operator
deparse(parse(text="a$'x'")[[1]]) # Conflates
name and character
deparse(parse(text="`*`(2)")[[1]]) # Result is
syntactically invalid
deparse(parse(text="`$`(a,b+2)")[[1]]) # Result is
syntactically invalid
e<-quote(if(x) X else Y); e[[3]]<-quote(if(T)3); deparse(e)# all
here
e <- quote(f(x)); e[[2]] <- quote((a=1))[[2]]; deparse(e) # and
below
e <- quote(f(Q=x)); e[[2]] <- quote((a=1))[[2]]; deparse(e)# need
parens
e <- quote(while(x) 1); e[[2]] <- quote((a=1))[[2]]; deparse(e)
e <- quote(if(x) 1 else 2); e[[2]] <- quote((a=1))[[2]];
deparse(e)
e <- quote(for(x in y) 1); e[[3]] <- quote((a=1))[[2]]; deparse(e)
In addition, the bug illustrated below was fixed, which was fixed
(differently) in R-3.0.0:
a<-quote(f(1,2)); a[[1]]<-function(x,y)x+y; deparse(a) # Omits
parens
o Fixed the following bug (also in R Core versions to at least
R-3.2.2):
> parse()
?'\12a\x.'
Error: '\x' used without hex digits in character string starting
"'\1a\x"
Note that the "2" has disappeared from the error message. This
bug also affected the results of getParseData.
o Fixed a memory leak that can be seen by running the code below:
> long <- paste0 (c('"',
rep("1234567890",820), '\x."'), collapse="")
> for (i in 1:1000000) try (e <- parse(text=long), silent=TRUE)
The leak will not occur if 820 is changed to 810 in the above.
This bug also exists in R Core versions to at least R-3.2.2.
o Entering a string constant containing Unicode escapes that was
9999 or 10000 characters long would produce an error message
saying "String is too long (max 10000 chars)". This has been
fixed so that the maximum now really is 10000 characters. (Also
present in R Core versions, to at least R-3.2.2.)
o Fixed a bug that caused the error caret in syntax error reports
to be misplaced when more than one line of context was shown.
This was supposedly fixed in R-3.0.2, but incorrectly, resulting
in the error caret being misplaced when only one line of context
is shown (in R Core versions to at least R-3.2.2).
