Wacek Kusnierczyk wrote:
(a) do not descend recursively into the function part (first element)
of a call
(b) do descend, unless it is a name
if it is a name, how would you descend?
By calling a recursive function which has it as the argument. It's not a
problem unless you want it to be (first you descend into the first
element on a call, then realize that it is a name). There are
essentially three possibilities (cutting some red tape):
> f <- function(e) if (is.name(e))
print(e) else if(is.call(e)) invisible(lapply(e,f))
> f(~ fo(o)())
`~`
fo
o
> f <- function(e) if (is.name(e))
print(e) else if(is.call(e)) invisible(lapply(e[-1],f))
> f(~ fo(o)())
> f <- function(e) if (is.name(e)) print(e) else
if(is.call(e)) invisible( if(is.name(e[[1]]))
lapply(e[-1],f) else lapply(e,f))
> f(~ fo(o)())
o
The first two are essentially the current all.names and all.vars. The
third is the one that you seem to expect. Notice that it gets rather
more complicated than the others.
> one legitimate reason is to keep the syntax/semantics clean (worship the
god of boring pedantry).
be this not enough, a practical example could certainly be found, though
admittedly the above were made up for the discussion.
But can you be sure that there is no legitimate reason for expecting the
current behaviour?
--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
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~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907
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