[R] identical calls are not equal !?

oehl_list@gmx.de oehl_list at gmx.de
Wed Jun 12 16:23:01 CEST 2002

Can please someone familiar with the R internals enlighten me on the
following strange observation:

# this is IDENTICAL as expected
identical(substitute(substitute()), substitute(substitute()))
# but NOT EQUAL !????
substitute(substitute()) == substitute(substitute())

# I originally found it on 
t2 <- function(e){
t2(substitute(x==y, list(y=y)))[1]
# I would expect all of the following to be equal !?
t2(substitute(x==y, list(y=y)))[1] == substitute(substitute())
t2(substitute(x==y, list(y=y)))[1] == substitute(substitute())[1]
identical(t2(substitute(x==y, list(y=y)))[1], substitute(substitute())[1])
identical(t2(substitute(x==y, list(y=y)))[1], substitute(substitute()))
identical(t2(substitute(x==y, list(y=y)))[1], quote(substitute()))

I have a guess that .Primitive("==") on method dispatch somehow treats its
first argument different from its second. However, if so, is this intended? Or
is it an unavoidable implementation issue? Or a bug?


Jens Oehlschlägel


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