[Rd] anonymous function parsing bug?
Wilm Schumacher
wilm.schumacher at gmail.com
Fri Oct 21 17:43:44 CEST 2016
Hi,
thx for the reply. Unfortunately that is not a simplified version of the
problem. You have a function, call it and get the result (numeric in,
numeric out in that case). For simplicity lets use the "return" case:
##
foobar<-function(x) { return(sqrt(x)) }(2)
##
which is a function (numeric in, numeric out) which is defined, then
gets called and the return value is a function (with an appendix of
"(2)" which gets ignored), not the numeric.
In my opinion the result of the expression above should be a numeric
(1.41... in this case) or an parser error because of ambiguities.
e.g. in comparison with node.js
##
function(x){
return(2*x)
}(2);
##
leads to
##
SyntaxError: Unexpected token (
##
Or Haskell (and basically every complete functional languange)
##
(\x -> 2*x) 2
##
which leads to 4 (... okay, that is not comparable because here the
parenthesis make a closure which also works in R or node.js).
However, I think it's weird that
> ( function(x) { return(2*x) } ( 2 ) ) (3)
is a legal statement which results to 6 and that the "(2)" is basically
ignored by the parser.
Furthermore it is very strange, that
##
f1<-function(x) { print(2*x) }(2)
f1(3)
##
does the command and gives an error ("attempt to apply non-function") and
##
f2<-function(x) { return(2*x) }(2)
f2(3)
##
is perfectly fine. Thus the return statement changes the interpretation
as a function? Or do I miss something?
Best wishes
Wilm
Am 21.10.2016 um 17:00 schrieb William Dunlap:
> Here is a simplified version of your problem
> > { sqrt }(c(2,4,8))
> [1] 1.414214 2.000000 2.828427
> Do you want that to act differently?
>
>
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com <http://tibco.com>
>
> On Fri, Oct 21, 2016 at 6:10 AM, Wilm Schumacher
> <wilm.schumacher at gmail.com <mailto:wilm.schumacher at gmail.com>> wrote:
>
> Hi,
>
> I hope this is the correct list for my question. I found a wired
> behaviour of my R installation on the evaluation of anonymous
> functions.
>
> minimal working example
>
> ###
> f<-function(x) {
> print( 2*x )
> }(2)
>
> class(f)
>
> f(3)
>
> f<-function(x) {
> print( 2*x )
> }(4)(5)
>
> f(6)
> ###
>
> leads to
>
> ###
> > f<-function(x) {
> + print( 2*x )
> + }(2)
> >
> > class(f)
> [1] "function"
> >
> > f(3)
> [1] 6
> Error in f(3) : attempt to apply non-function
> >
> > f<-function(x) {
> + print( 2*x )
> + }(4)(5)
> >
> > f(6)
> [1] 12
> Error in f(6) : attempt to apply non-function
>
> ###
>
> is this a bug or desired behavior? Using parenthesis of coures
> solves the problem. However, I think the operator precedence could
> be the problem here. I looked at the "./src/main/gram.y" and I
> think that the line 385
> | FUNCTION '(' formlist ')' cr expr_or_assign %prec LOW
> should be of way higher precedence. But I cannot forsee the side
> effects of that (which could be horrible in that case).
>
> If this is the desired behaviour and not a bug, I'm very
> interested in the rational behind that.
>
> Best wishes,
>
> Wilm
>
> ps:
>
> $ R --version
> R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
>
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