From plummer@iarc.fr  Thu Nov  6 09:28:08 1997
From: plummer@iarc.fr (Martyn Plummer)
Date: Thu, 06 Nov 1997 10:28:08 +0100
Subject: R-alpha: "invisible" (yet again): a more problematic bug[let]
References: <md5:4C26491E69F1EF6D2FB938607D06BE19>
Message-ID: <34618DA8.23AA175C@iarc.fr>

maechler@stat.math.ethz.ch wrote:
> 
> Try this  (all versions of R from  0.49 to 0.60):
> 
> test0 <- function() c(1,2)
> test  <- function(two = FALSE)        c(1, if(two) 2)
> testR <- function(two = FALSE) return(c(1, if(two) 2))
> 
> test0()# 1 2 as it should
> test() # <<<<<<<<<<<<<<<<<<<<<< INVISIBLE! @#$@!
> test(T)# 1 2
> print(test())
> print(test(T))
> 
> testR() # ok; NOT invisible...
> testR(T)# 1 2

The problem seems to be in do_if (eval.c) where the R_Visible flag
is set to 0. Set it to 1 instead and your functions will work
properly. You also get

R>if(F) 2
NULL

instead of 
R>if(F) 2
R>

which is consistent with S-PLUS.

Martyn
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R-alpha: "invisible" (yet again): a more problematic bug[let]
Martyn Plummer