Message-ID: <20030422053136.GB28956423@genome.cbs.dtu.dk>
Date: 2003-04-22T05:31:36Z
From: Laurent Gautier
Subject: lexical scope
In-Reply-To: <200304220407.h3M47dXu016904@r.hankin.sges.auckland.ac.nz>
On Tue, Apr 22, 2003 at 04:07:39PM +1200, Robin Hankin wrote:
> Hi everyone
>
> another documented feature that was a bit unexpected for me:
>
> R> x <- 19
> R> f <- function(t){t+x}
> R> f(100)
> [1] 119
>
> --as expected: x is visible from within f()
> ..but...
>
>
> R> g <- function(a){x <- 1e99 ; return(f(a))}
> R> g(4)
> [1] 23
>
> --the "x" that is visible from within g() is just 19, which is not the
> one I expected it to find.
>
>
> R> rm(x)
> R> g(4)
> Error in f(a) : Object "x" not found
>
> --g() looks in the first search path place and finds it empty,
> returning an error.
>
>
> QUESTIONS:
> Why doesn't g() "keep looking" ?
> How do I tell g() where to find x?
> Where to look for documentation for this?
>
(TENTATIVE) ANSWERS:
1- becase the enclosing frame for f is .GlobalEnv.
2- f <- function(t){t+get("x", envir=parent.frame())}
3- R language definition p.22 is a place to start
Hopin' it helps,
L.
>
>
> --
>
> Robin Hankin, Lecturer,
> School of Geography and Environmental Science
> Tamaki Campus
> Private Bag 92019 Auckland
> New Zealand
>
> r.hankin at auckland.ac.nz
> tel 0064-9-373-7599 x6820; FAX 0064-9-373-7042
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
--
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currently at the National Yang-Ming University in Taipei, Taiwan
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Laurent Gautier CBS, Building 208, DTU
PhD. Student DK-2800 Lyngby,Denmark
tel: +45 45 25 24 89 http://www.cbs.dtu.dk/laurent