Gabor Grothendieck wrote:
Note that
rm(i)
for(j in 1:4) F(j)
raises an error due to scoping issues.
Yes. This has nothing to do with lazy evaluation, and everything to do
with scoping: f is not defined in the scope of F, so does not know about
its variables (nor those in the implicit loop of lapply()).
Notice also that in
lapply(1:4,function(i) F(i))
it would be pretty weird if lapply would behave differently depending on
the name of formal arguments of the function, i.e. if
lapply(1:4,function(meep) F(meep))
gave a different result. And f() depends on looking for a variable i
outside of the function.
On Sun, Jan 18, 2009 at 10:02 PM, <markle...@verizon.net> wrote:
I've been going back to old difficult R-list "evaluation" emails that I save
in order to understand evaluation better and below still confuses me. Could
someone explain why A) works and B) doesn't. A variant of below is in the
Pat's Inferno book also but I'm still not clear on what is happening.
Thanks.
f <- function() {
# FORCING i here doesn't help
i*i
}
F <- function(i) {
force(i)
print(f())
}
A) THIS WORKS
for ( i in 1:4 ) {
F(i)
}
B) THIS DOESN'T
lapply(1:4,function(i) F(i))
--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907
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