On 7/31/2008 2:08 PM, Ken Williams wrote:
On 7/31/08 11:01 AM, "hadley wickham" <[EMAIL PROTECTED]> wrote:
I think that would be a very hard task -
Well, at least medium-hard. But I think significant automatic steps could
be made, and then a human can take over for the last few steps. That's why
I was enquiring about "tools" rather than a complete solution.
Does R provide facilities for introspection or interrogation of expression
objects? I couldn't find anything useful on first look:
You can index an expression as a list:
> e <- expression(foo <- 5 * bar)
>
> e[[1]]
foo <- 5 * bar
> str(e[[1]])
language foo <- 5 * bar
expression() returns a list of language objects, and we only asked for
one. We can look inside it:
> e[[1]][[1]]
`<-`
The as.list function is also useful:
> as.list(e[[1]])
[[1]]
`<-`
[[2]]
foo
[[3]]
5 * bar
and proceed recursively:
> as.list(e[[1]][[3]])
[[1]]
`*`
[[2]]
[1] 5
[[3]]
bar
Duncan Murdoch
>
>> methods(class="expression")
> no methods were found
>> dput(expression(foo <- 5 * bar))
> expression(foo <- 5 * bar)
>> str(expression(foo <- 5 * bar))
> expression(foo <- 5 * bar)
>
>
>> it's equivalent to taking a
>> long rambling conversation and then automatically turning it into a
>> concise summary of what was said. I think you must have human
>> intervention.
>
> It's not really equivalent, natural language has ambiguities and
subtleties
> that computer languages, especially functional languages, intentionally
> don't have. By their nature, computer languages can be turned into parse
> trees unambiguously and then those trees can be manipulated.
>
> But coincidentally I work in a Natural Language Processing group, and
one of
> the things we do is create exactly the kind of concise summaries you
> describe. =)
>
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