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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