[Rd] anonymous function parsing bug?

Wilm Schumacher
Fri, 21 Oct 2016 15:43:44 -0000

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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>


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