From Martin Maechler <maechler@stat.math.ethz.ch>  Thu Nov  6 10:55:17 1997
From: Martin Maechler <maechler@stat.math.ethz.ch> (Martin Maechler)
Date: Thu, 6 Nov 1997 11:55:17 +0100
Subject: R-alpha: "invisible" : R_INVISIBLE .. -- repeat{} gives BOMB
In-Reply-To: <34618DA8.23AA175C@iarc.fr> (message from Martyn Plummer on Thu,
 06 Nov 1997 10:28:08 +0100)
Message-ID: <199711061055.LAA05033@sophie.ethz.ch>

>>>>> "Martyn" == Martyn Plummer <plummer@iarc.fr> writes:

    Martyn> 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

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

    R> if(F) 2
    Martyn> NULL

    Martyn> instead of
    R> if(F) 2
    R> 

    Martyn> which is consistent with S-PLUS.

Wow, this was quick and precise,  thank you !!

I investigated some more:  
	R_VISIBLE is set to 0  ``R_Visible = 0;''
	 also in other places in eval.c :

 line	C function
		
  344:	  do_if
  436:	  do_for
  480:	  do_while
  515:	  do_repeat
  720:    \
  727:     > do_set
  738:    /
  ^^^
(line numbers from current 0.60)

In my opinion, only the three cases in do_set ("<-" things) should have
the invisibility flag...

	
testwh <- function(n = 1) c(1, while(n > 1) {n <- n-1; n})
testwh() # invisible !
testwh(2)
print(testwh()) # 1
print(testwh(2))# 1 1
##-- in Splus, both are visible

###-------- THIS IS EVEN WORSE:   Segmentation violation !!! -----

testrep <- function(n = 1) c(1, repeat {n <- n-1; if(n<=0) break})
testrep()
##R : Process R:1 segmentation violation at Thu Nov  6 11:36:27 1997


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R-alpha: "invisible" : R_INVISIBLE .. -- repeat{} gives BOMB
Martin Maechler