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Sun Oct 14 16:52:10 CEST 2007

## removed from purrr.tex

\section{The Big Picture}

Purrr can be used in its own right, but it is good to note that Purrr
is part of the Brood system, which is an experiment to combine ideas
from Forth, (PLT) Scheme and compositional functional languages into a
single coherent language tower. Purrr can be seen as an
\emph{introspective boundary} in this language tower: the core of
Purrr is to be the basis of this language tree, but the scope of Purrr
is limited to a low--level language with Forth syntax and semantics
and some meta--programming facilities disguised as Forth macros. For
example, it is not possible to access the intermediate functional
macro representation directly from within Purrr at this moment; this
still requires extension of the compiler itself using the Scheme and
CAT languages. This separation between the Purrr language and its
implementation serves to to keep the programmer interface to Purrr as
simple as possible, while the detais of the language tower are worked
out to eventually lead to a more coherent whole. Purrr by itself is
reasonably coherent, although it is somewhat limited in full
reflective power by this language barrier. Eventually, Purrr should be
just an interface (with Forth syntax) to the low level core of the
compositional language tower in Brood.

Because Purrr is implemented only for the Microchip PIC18
architecture, there is no tested \emph{standard} machine layer: most
functionality is fairly tied with the PIC18. I am confident however,
that refining the split of the current code base into a shared and
platform specific component is fairly straightforward. Due to the ease
with which to create an impedance match in a Forth like language, I am
refraining from an actual specification of this standard layer until
the next platform is introduced.  By consequence, the border between
the machine model and the library might shift a bit.

Purrr's macro system is the seed for a declarative functional
language. Such a language would have no explicit macro/forth
distinction as in Purrr.


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