turning R expressions into functions?

list(...) evaluates the things in ...
E.g.,

   > f0 <- function(x, ...) list(...)
   > f0(1, warning("Hmm"), stop("Oops"), cat("some output\n"))[[2]]

   Error in f0(1, warning("Hmm"), stop("Oops"), cat("some output\n")) : Oops
   In addition: Warning message:
   In f0(1, warning("Hmm"), stop("Oops"), cat("some output\n")) : Hmm

You can use the odd idiom substitute(...()) to get the unevaluated ... arguments:

   > f1 <- function(x, ...) substitute(...())
   > f1(1, warning("Hmm"), stop("Oops"), cat("some output\n"))

   [[1]]
   warning("Hmm")

   [[2]]
   stop("Oops")

   [[3]]
   cat("some output\n")


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 S Ellison
Sent: Monday, July 23, 2012 2:12 PM
To: Jochen Vo?
Cc: r-help at r-project.org
Subject: Re: [R] turning R expressions into functions?

One of the things I would love to add to my package would be the
ability to compare more than two expressions in one call.  But
unfortunately, I haven't found out so far whether (and if so, how) it
is possible to extract the elements of a "..." object without
evaluating them.

Have a look at match.call.

... or use
dotlist <- list(...)

to get a list of everything included in ...

S Ellison

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