Puzzled by eval

I am currently puzzled by a seach path behavior.  I have a library of a dozen routines
getlabs(), getssn(), getecg(), ... that interface to local repositories and pull back
patient information.  All have a the first 6 arguments in common, and immediately call a
second routine to do initial processing of these 6.  The functions "joe" and "fred" below
capture the relevant portion of them.
    My puzzle is this: the last test in the "test" file works fine if these routines are
sourced and executed at the command line, it fails if the routines are bundled up and
loaded as a library. That test is motivated by a user who called his data set "t", and
ended up with a match to base:::t instead of his data, resulting in a strange error
message out of model.frame  --- you can always count on the users!  (There are a few hundred.)
     I'm attempting to be careful with envr and enclos arguments -- how does base end up
earlier in the search path?   Perhaps this is clearly stated in the docs and just not
clear to me?  A working solution to the dilemma is of course more than welcome.

Terry Therneau


code:
joe <- function(id, data, subset, na.action, date1, date2, other.args) {
      Call <- match.call()
      if (!missing(data)) temp <- fred(Call)

      temp
}

fred <- function(Call) {
      # get a first copy of the id and date variables
      index <- match(c("id", "date1", "date2"), names(Call), nomatch=0)
      temp <- Call[c(1, index)]
      temp[[1]] <- as.name("list")

      pf <- parent.frame(2)  # the caller of the caller
      data <- eval(Call$data, envir=pf)

      ldata <- eval(temp, data, enclos= pf)
      date1 <- ldata$date1
      date2 <- ldata$date2

      # Users are allowed great flexibility with dates.  Both can be given
      # as length 1 parameters, both can be in the data set, or one could
      # be in each place.  Call model.frame with a built up formula that
      # includes the id and any dates of length greater than 1. This allows
      # subset and na.action to be applied in the usual way.
      index <- match(c("data", "subset", "na.action"), names(Call), nomatch=0)
      temp <- Call[c(1, index)]
      temp[[1]] <- as.name("model.frame")
      tform <- "~ id"
      if (length(date1) > 1 && is.name(Call$date1))
          tform <- paste(tform, "+", as.character(Call$date1))
      if (length(date2) > 1 && is.name(Call$date2))
          tform <- paste(tform, "+", as.character(Call$date2))

      tform <- as.formula(tform)
      environment(tform) <- pf
      temp$formula <- tform
      mf <- eval(temp, enclos=pf)

      # At this point the real routine has checks for legal dates, date1 <= date2, etc
      #  It returns the tidied up id, date1, date2 vectors.
      list(ldata=ldata, mf=mf)
}

test:
library(puzzle)
tdata <- data.frame(id=1:10,
                      start=as.Date(paste0("1999/", 1:10, "/25")))
xdate <- as.Date(paste0(2001:2010, "/03/10"))

joe(id, tdata, date1= "2001/10/11", date2= xdate[2])
joe(id, tdata, date1=start, date2=xdate)

sqrt <- xdate
cos <- tdata

joe(id, cos, date1=start, date2=sqrt)

DESCRIPTION:
Title: A puzzle
Priority: optional
Package: puzzle
Version: 1.1-1
LazyLoad: Yes
LazyData: Yes
Authors at R: c(person(c("Terry", "M"), "Therneau",
                      email="therneau.terry at mayo.edu",
                  role=c("cre")))
Description: What gives with my tests?
License: GPL

NAMESPACE:
export("joe")