Is function(x){x}(5) a valid expression?
The syntax
expression(arg)
means to call the value of 'expression' as a function with argument 'arg'.
Hence you can do things like
{ function(x)x^2 } (11:13) # gives 121, 144, 169
or, weirder,
eval(call("function", pairlist(x=NULL, base=2), quote(log(x,base)))) (512) # gives 9
If 'expression' is not a function you get an error of the sort you saw, similar
to what you would get if you did
x <- 1:10
x(17)
The parser doesn't know if 'expression' will evaluate to a function or not
so it accepts it and you get the error at run time.
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
Of Jamie Olson
Sent: Tuesday, November 13, 2012 10:33 AM
To: r-help at r-project. org
Subject: [R] Is function(x){x}(5) a valid expression?
I was surprised to notice that statements like:
h = function(...){list(...)}(x=4)
do not throw syntax errors. R claims that 'h' is now a function, but I
can't seem to call it.
h = function(x){list(x)}(4)
is(h)
[1] "function" "OptionalFunction" "PossibleMethod"
h()
Error in list(x) : 'x' is missing
h(4)
Error in h(4) : attempt to apply non-function
What's going on? Jamie Olson [[alternative HTML version deleted]]
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