From james.f.hester at gmail.com  Wed Jul 29 23:33:11 2015
From: james.f.hester at gmail.com (Jim Hester)
Date: Wed, 29 Jul 2015 17:33:11 -0400
Subject: [Rd] Mapping parse tree elements to tokens
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As Michael guessed my main use cases was code analysis.  A concrete example
where this would help is with my test code coverage tool covr.  There is
currently a bug when tracking coverage for if / else statements when the
clauses do not contain brackets (https://github.com/jimhester/covr/issues/39).
Because only one source reference is generated in this case (because it is
parsed as a single expression), it is not possible to track each of the
clauses separately.  While I can get the source reference for the entire
statement, in order to extract the if/else clauses I need to either use the
tokenized information from getParseData(), or re-parse the entire if / else
expression by hand (which seems prone to error to me).

Another example of where this would help is linking comments to
expressions.  While I know this topic has been discussed previously (
https://stat.ethz.ch/pipermail/r-devel/2009-March/052731.html) and I am
fine with the default parser dropping comments, having the ability to map
the more detailed tokens back to the parse tree would allow the comments to
be annotated to their closest expression.

Of the three options you propose I think simply supplying the index as an
additional column from the getParseData() output would be the most
straightforward to implement and use.

While it is true that you can get most of the way there with the current
source references as Michael mentions in some cases having more fine
grained location information is useful and there is no great way to get
there currently without re-parsing the full expressions from the source
reference.

The current getParseData output is already very implementation specific so
I don't think it would be a great additional support burden to add the
indexing information.  Likely the whole function would have to be removed
if a different parsing method was used.

Regardless I am glad others have shown some interest in this issue, thank
you for taking the time to read and respond!

Jim

On Wed, Jul 29, 2015 at 2:47 PM, Duncan Murdoch <murdoch.duncan at gmail.com>
wrote:

> On 29/07/2015 2:30 PM, Michael Lawrence wrote:
>
>> Probably need a generic tree based on "ParseNode" objects that
>> associate the line information with the symbol (for leaf nodes). As
>> Duncan notes, it should be possible to gather that from the table.
>>
>> But it would be nice if there was an "expr" column in the parse data
>> column in addition to "text". It would contain the parsed object.
>> Otherwise, to use the table, one is often reparsing the text, which
>> just seems redundant and inconvenient.
>>
>
> Can you (both Jim and Michael) describe the uses you might have for this?
> There are lots of possible changes that could make this information
> available:
>
>  - attach to each item in the parse tree, as the parser package did.  (Bad
> idea for general use which is why I dropped it, but
> it could be done as a special option to parse, if you aren't planning to
> evaluate the expression.)
>  - give the index into the parse tree of each item, i.e. c(1,1), c(1,2),
> c(1,3) in the example below, or just 1,2,3 along with a function to
> reconstruct the full path.
>  - give a copy of the branch of the parse tree, as Michael suggests.
>
> etc.  Which is best for your purposes?
>
> Duncan Murdoch
>
>
>> Michael
>>
>> On Wed, Jul 29, 2015 at 9:43 AM, Duncan Murdoch
>> <murdoch.duncan at gmail.com> wrote:
>> > On 29/07/2015 12:13 PM, Jim Hester wrote:
>> >>
>> >> I would like to map the parsed tokens obtained from
>> utils::getParseData()
>> >> to the parse tree and elements obtained by base::parse().
>> >>
>> >> It looks like back when this code was in the parser package the parse()
>> >> function annotated the elements in the tree with their id, which would
>> >> allow you to perform this mapping.  However when the code was included
>> in
>> >> R
>> >> this functionality was removed.
>> >
>> >
>> > Yes, not all elements of the parse tree can legally have attributes
>> > attached.
>> >>
>> >>
>> >> ?getParseData states
>> >>    The ?id? values are not attached to the elements of the parse
>> >>            tree, they are only retained in the table returned by
>> >>            ?getParseData?.
>> >>
>> >> Is there another way you can map between the getParseData() tokens and
>> >> elements of the parse tree that makes this additional annotation
>> >> unnecessary?  Or is this simply not possible?
>> >
>> >
>> > I think you can't get to it, though you can get close by looking at the
>> id &
>> > parent values in the table.  For example,
>> >
>> >  code <- "x + (y + 1)"
>> >  p <- parse(text=code)
>> >
>> > getParseData(p)
>> >    line1 col1 line2 col2 id parent     token terminal text
>> > 15     1    1     1   11 15      0      expr    FALSE
>> > 1      1    1     1    1  1      3    SYMBOL     TRUE    x
>> > 3      1    1     1    1  3     15      expr    FALSE
>> > 2      1    3     1    3  2     15       '+'     TRUE    +
>> > 13     1    5     1   11 13     15      expr    FALSE
>> > 4      1    5     1    5  4     13       '('     TRUE    (
>> > 11     1    6     1   10 11     13      expr    FALSE
>> > 5      1    6     1    6  5      7    SYMBOL     TRUE    y
>> > 7      1    6     1    6  7     11      expr    FALSE
>> > 6      1    8     1    8  6     11       '+'     TRUE    +
>> > 8      1   10     1   10  8      9 NUM_CONST     TRUE    1
>> > 9      1   10     1   10  9     11      expr    FALSE
>> > 10     1   11     1   11 10     13       ')'     TRUE    )
>> >
>> >
>> > Now p is an expression, with the parse tree in p[[1]].  From the table,
>> we
>> > can see that the root node has id 15, and 3 nodes have that as a parent.
>> > Those would be p[[c(1,1)]], p[[c(1,2)]], p[[c(1,3)]].  The tricky part
>> is
>> > the re-ordering:  those correspond to `+`, x, and (y+1) respectively,
>> not
>> > the order they appear in the original source or in the table.
>> Generally the
>> > function call appears first in the parse tree, but I'm not sure you
>> could
>> > always recognize which is the function call by looking at the table.
>> >
>> > Duncan Murdoch
>> >
>> > ______________________________________________
>> > R-devel at r-project.org mailing list
>> > https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>
>

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[Rd] Mapping parse tree elements to tokens
Jim Hester