[Rd] Proper way to drop 'srcref' from an expression created via substitute(function() ...)?

[Henrik Bengtsson]

Thanks. /Henrik

On Thu, Dec 12, 2013 at 5:27 PM, Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:
> On 13-12-12 7:57 PM, Henrik Bengtsson wrote:
>>
>> First, why does this expression have a 'srcref' element:
>>
>>> exprA <- substitute(function(x) a*x, list(a=2))
>>> print(exprA)
>>
>> function(x) 2 * x
>>>
>>> str(as.list(exprA))
>>
>> List of 4
>>   $ : symbol function
>>   $ :Dotted pair list of 1
>>    ..$ x: symbol
>>   $ : language 2 * x
>>   $ :Class 'srcref'  atomic [1:8] 1 20 1 34 20 34 1 1
>>    .. ..- attr(*, "srcfile")=Classes 'srcfilecopy', 'srcfile'
>> <environment: 0x00000000111feaf8>
>>
>> whereas this does not:
>>
>>> exprB <- substitute(a*x, list(a=2))
>>> print(exprB)
>>
>> 2 * x
>>>
>>> str(as.list(exprB))
>>
>> List of 3
>>   $ : symbol *
>>   $ : num 2
>>   $ : symbol x
>>
>
> Function definitions get srcrefs.
>
>
>>
>> Second, what is the proper way to drop that 'srcref' element in
>> 'exprA'?  I can think of either
>>
>> exprC <- exprA
>> exprC[[4L]] <- NULL
>
>
> That should be best.
>
> Duncan Murdoch
>
>>
>> or
>>
>> exprC <- parse(text=deparse(exprA))
>>
>> Anything better/safer?
>>
>>
>> BACKGROUND:
>> The reason for this is that I wish to create a function dynamically
>> via variable substitution such that when printed, the function
>> displays the substituted values, e.g.
>>
>>> fcnA <- eval(exprA)
>>> print(fcnA)
>>
>> function(x) a*x
>>
>> versus
>>
>>> fcnC <- eval(exprC)
>>> print(fcnC)
>>
>> function(x) 2 * x
>>
>> Thanks,
>>
>> Henrik
>>
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>