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One final area that requires some attention is the representation of
statistical models. Currently there is no analogue to the formula data
used in S [2]. Such a mechanism needs to
be added. But there is a weakness to the S mechanism that should not
be duplicated. S code for fitting models described by formulas
contains rather awkward and brittle constructs to locate the data a
formula refers to. Since formulas are typically created by a user in a
context where the data are available, it seems natural to use the
concept of lexical scope and make a formula capture the relevant
portion of the environment in which it is created, thus acting like a
closure. This environment would then provide the default data values
for fitting functions.
Luke Tierney
5/27/1998