From maechler@stat.math.ethz.ch  Sat Mar 23 18:01:33 2002
From: maechler@stat.math.ethz.ch (maechler@stat.math.ethz.ch)
Date: Sat, 23 Mar 2002 19:01:33 +0100 (MET)
Subject: [Rd] rare bad bug in sys.function() {or match.arg()} (PR#1409)
Message-ID: <200203231801.TAA04756@pubhealth.ku.dk>

>>>>> "PD" == Peter Dalgaard BSA <p.dalgaard@biostat.ku.dk> writes:

    PD> maechler@stat.math.ethz.ch writes:
    >> I found this tracing a bug when experimenting with a new
    >> sort() function using match.arg().
    >> 
    >> It was triggered because mosaicplot.default(.) has an
    >> argument called `sort' and calls itself the sort()
    >> function in which I was using match.arg()...
    >> 
    >> Here is (input for) a small clean example :
    >> 
    >> #### bad match.arg() // sys.function() bug : #### MM,
    >> 22.3.2002
    >> 
    >> callme <- function(a = 1, mm = c("Abc", "Bde")){ mm <-
    >> match.arg(mm) cat("mm = "); str(mm) invisible() }
    >> 
    >> 
    >> ## These are as desired callme() callme(mm="B")
    >> 
    >> mycaller <- function(x = 1, callme = pi) { callme(x) }
    >> 
    >> mycaller() ##-> mm = NULL
    >> 
    >> ## but should give "Abc !!
    >> 
    >> -------
    >> 
    >> Explanation :
    >> 
    >> In match.arg(), there's formal.args <-
    >> formals(sys.function(sys.parent())) and you can check
    >> that sys.function(sys.parent()) gives the number pi
    >> instead of the the callme function !! :
    >> 
    >> debug(match.arg) mycaller() .....

    PD> This looks suspiciously like the same issue as
    PD> PR#921. Did someone have plans to change the context
    PD> stack handling so that we could have a "real"
    PD> sys.function()? To quote my own followup to PR#921:

    PD> "The problem is that we only actually store the call in
    PD> the context structure, not the function, so sys.function
    PD> has to grab the call, take the 1st element, and
    PD> reevaluate it in the parent frame."

hmm, bad news.  
but couldn't it try to do the equivalent of
    get(name, mode = "function")
instead of simply
    get(name)
?

[I think this *must* be fixed, at least we'd have to program
  around it in match.arg()]

Martin

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[Rd] rare bad bug in sys.function() {or match.arg()} (PR#1409)
maechler@stat.math.ethz.ch