[viff-devel] Small VIFF language parser

[Martin Geisler]

Hi everybody,

We have talked on and off about making a front-end compiler for VIFF and
today I figured that I would try making such a guy...

So far it can only parse a simple language and spit out something which
looks like equivalent Python code in which both branches of
if-statements are run. So a program like this:

  if a:
    x = y
    if b:
      x = z
    else:
      x = w
    fi
  fi

is transformed into this

  x = (a * y + (1 - a) * x)
  x = (a * b * z + (1 - a * b) * x)
  x = ((1 - a * b) * w + (1 - (1 - a * b)) * x)

which one could plug into a VIFF skeleton and run (not yet done).

The idea is that the conditions in if-statements are pushed down to all
assignments done in the then- and else-branches, nothing more.

This is just a quick test to make people start thinking about what we
want in such a language and to make people think about what kind of
transformation we can do and which we cannot do.

The program is attached below -- you will need to grab simplegeneric and
PLY (Python Lex-Yacc) to use it, but both modules are easy to install:

  http://pypi.python.org/pypi/simplegeneric
  http://www.dabeaz.com/ply/

You run the program by giving it the name of a file to parse and it will
tell you the results on stdout.

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-- 
Martin Geisler