[R] Default argument not passed to subfunction when argument name matches default expression

[Tierney, Luke]

Compiled code gives a better error message (not clear why the
interpreter doesn't do this as well):

> cmpfun(foo)()
Error in bar() :
  promise already under evaluation: recursive default argument reference or ear$

The environment in which default arguments are evaluated is the
environment of the function call itself, not the environment of the
caller or the lexical enclosure (the same here). So the two 'y' used
in function(y = y) refer to the same binding, hence circular
reference. If you use

foo <- function (z = 2) {
     bar <- function (y = z) y^2
    bar()
}

then there is no problem:

> foo()
[1] 4
> cmpfun(foo)()
[1] 4

Best,

luke

Luke Tierney
Chair, Statistics and Actuarial Science
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
   Actuarial Science
241 Schaeffer Hall                  email:   luke-tierney at uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu


________________________________________
From: r-help-bounces at r-project.org [r-help-bounces at r-project.org] on behalf of Philippe Grosjean [phgrosjean at sciviews.org]
Sent: Monday, March 31, 2014 9:40 AM
To: R Help
Subject: [R] Default argument not passed to subfunction when argument name      matches default expression

Hello,

I have difficulties to understand this one:

foo <- function (y = 2) {
    bar <- function (y = y) y^2
    bar()
}
foo()
#! Error in y^2 : 'y' is missing
foo(3)
#! Error in y^2 : 'y' is missing

Note that this one works:

foo <- function (y = 2) {
    bar <- function (y = y) y^2
    bar(y) # Not using default value for y= argument
}
foo()
#! [1] 4
foo(3)
#! [1] 9

… as well as this one:

foo <- function (y = 2) {
    bar <- function (Y = y) Y^2
    bar() # Default, but different names for argument Y= and value 'y'
 }
foo()
#! [1] 4
foo(3)
#! [1] 9

Best,

PhG

> sessionInfo()
R version 3.0.2 (2013-09-25)
Platform: x86_64-apple-darwin10.8.0 (64-bit)

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base
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