Re: Python transformer for Guile?

[sen_ml at eccosys dot com]

i was serious when i said:

> i am very interested, but doubt how useful i would be ;-)  but i'd love
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> to learn what might be involved.  may be i can continue the trend of
> over-committing...

but, we'll see what happens.

> one thing i have wondered about in the past is whether the parsing
> code used to implement the source language (in this case python) can't
> be re-used for the task -- at least from a technical perspective.

mdj> This is an excellent idea.  Please check if you can extract this code
mdj> from the Python sources.  

my first pass through part of the sources for python lead me to a
directory called "Parser".  the name seemed suggestive, so i had a look
inside:

  Makefile.in
  acceler.c
  assert.h
  bitset.c
  firstsets.c
  grammar.c
  grammar1.c
  intrcheck.c
  listnode.c
  metagrammar.c
  myreadline.c
  node.c
  parser.c
  parser.h
  parsetok.c
  pgen.c
  pgen.h
  pgenmain.c
  printgrammar.c
  tokenizer.c
  tokenizer.h

the final goals of make-ing in this directory appear to be

  -an executable called pgen
  -two object files named myreadline.o and intrcheck.o

the comments in pgen.c suggest that pgen is a parser generator.
are you familiar w/ typical uses of pgen?

from another angle, looking through pythonrun.c, lead me to
PyParser_ParseFile (parsetok.c), which in turn lead me to
PyTokenizer_FromFile (tokenizer.c).  i have a feeling i may at least
be in the ballpark here.

mdj> It might be a good idea to let it generate an intermediate
mdj> representation (Python with Scheme syntax) and then use a
mdj> translator, written in Scheme, to generate the Scheme code.  (The
mdj> translator can have the shape of an evaluator (see e.g. SICP) but
mdj> instead of computing values, it computes code.)  

i think i just barely follow your idea.  i guess an intermediate
representation needs to be thought up.  i'll have to order sicp as i
don't have a copy -- any other suggested reading?  there's a good deal on
international shipping until the end of this month at a non-amazon
book store that i was thinking of taking advantage of anyway.

mdj> You'll also have to write a library with basic Python procedure
mdj> and data types.

i'm not sure i quite follow you here -- if i understood your idea
correctly, there are basically two large steps:

  1) python-code -> python-with-scheme-syntax
     performed by code resulting from modifying existing python parser (c)

  2) python-with-scheme-syntax -> scheme
     performed by translator code (scheme)

is it in step 2 that i will need this library?

> in python's case there might be licensing issues, i guess.

mdj> Python's license is compatible with GPL, so I don't think it'll be a
mdj> problem.

i guess all that is needed is to include the copyright and permission
notices are included.  does this count as compatible w/ gpl?

oops, my time/effort quota for this project for today has expired ;-)