[R] sub question

Wacek Kusnierczyk Waclaw.Marcin.Kusnierczyk at idi.ntnu.no
Tue Feb 3 14:24:18 CET 2009

Peter Dalgaard wrote:
> Gabor Grothendieck wrote:
>> On Sat, Jan 31, 2009 at 6:01 PM, Wacek Kusnierczyk
> th some additional boring pedantry wrt. ?gsubfn, which says:
>>> " If 'replacement' is a formula instead of a function then a one
>>>     line function is created whose body is the right hand side of the
>>>     formula and whose arguments are the left hand side separated by
>>>     '+' signs (or any other valid operator).  The environment of the
>>>     function is the environment of the formula.  If the arguments are
>>>     omitted then the free variables found on the right hand side are
>>>     used in the order encountered.  "
>>> to my little mind, all of 'paste', 'rep', 'nchar', and 'x' in the
>>> example above are *free variables* on the right of the formula.  you
>> The first three are functions, not variables.
> They are still free variables, subject to the same rules of variable
> lookup. Wacek is right: The RHS is scanned recursively for objects of
> mode "name" _except_ when they appear as function names (i.e. if
> subexpression e is mode "call", then forget e[[1]] and look at the
> arguments in as.list(e)[-1]. Not sure if this also happens if e[[1]]
> is not a name, e.g. in f(a)(b), do you get both a and b or just b?)

an interesting point.  the two calls to gsubfn below should, in this
particular case, be equivalent:


f = function(a) function(b) paste(a, b, sep="")
gsubfn('o', ~ f('o')(o), 'foo')
# "foooo"
gsubfn('o', ~ f(o)('o'), 'foo')
# the match seems to be ignored in the formula?

the following fails, too:

f = function(a) function() paste(a, a, sep="")
gsubfn('o', ~ f(o)(), 'foo')
# o won't capture the match

this as well, though it's rather different:

f = function() 'oo'
gsubfn('o', ~ f(), 'foo')
# really can't ignore the matched pattern if a formula is given?

while an average statistician may never write such rubbish code, these
are trivialized examples, and for a language advertised as one from the
functional family this sort of code is not so unusual and it may be
surprising that it fails.


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