Recursively parsing srcrefs
On 12/05/2011 3:59 PM, Hadley Wickham wrote:
Is it possible to "recursively" parse srcrefs to match the recursive structure of the underlying code? I'm interested in this because it's
I don't understand what you mean by that. It is certainly possible to walk through nested srcrefs, to zoom in on a particular location; that's what findLineNum() does.
Does the example below not help? Given the whole function, I want to
be able to walk down the call tree, finding the matching src refs as I
go. i.e. given f, how do I get f_inside?
f<- function(x = T) {
# This is a comment
if (x) return(4)
if (emergency_status()) return(T)
}
f_inside<- parse(text = "
# This is a comment
if (x) return(4)
if (emergency_status()) return(T)
")
I don't think you will get exactly the same thing. The problem is that srcrefs are attributes, and not all statements can have attributes attached to them, so the attributes are attached to the container of the statements. (For example, NULL is a statement and it is stored as the NULL object, but the NULL object can't have any attributes on it.) In those two cases, the containers are different, so I would expect some differences between what's in f and what's in f_inside (though I expect you could convert one to the other).
findLineNum doesn't quite do what I want - it works on the text of the srcref, not on the parse tree.
It searches through the parse tree for the smallest source ref that
contains a given line. So for example,
if(condition) {
blah
blah
blah
}
is a single statement, and there will be a srcref stored in its
container that goes from line N to line N+4. But it also contains the
compound statement
{
blah
blah
blah
}
and there will be srcrefs attached to that for each of the statements in
it. (I forget right now whether there are 3 or 4 statements there: R
treats braces in a funny way, and I'd have to look at an example to
check.) Each of the "blah"'s will get a srcref spanning one line, and
it will be stored in the container.
Here's another go at explaining what I want: h<- quote( 1 # one + # plus 2 # two ) h[[1]] extracts +. What can I do to extract "+ # plus" (on an object created in the appropriate manner to keep the srcref)? Is that even possible?
You can't easily do that. The current parser only attaches srcrefs down to the statement level, and the + is part of the statement which parses to "+ 2". (The 1 is a separate statement.) Duncan Murdoch
My eventual goal is something like
f<- function(x) {
# This is my function
T
}
g<- fix_logical_abbreviations(f)
which would be equivalent to
g<- function(x) {
# This is my function
TRUE
}
That last display looks like a bug indeed. I'll take a look.
The key seems to be a leading newline: parse(text = "\nx") parse(text = "x") Hadley