Railroad track syntax diagrams

[Paul McGuire]

Back in the mid-90's, Kees Blom generated a set of railroad syntax diagrams
for Python
(http://python.project.cwi.nl/search/hypermail/python-1994q3/0286.html).
This pre-dates any Python awareness on my part, but I'm sure this would have
been version 1.3 or something.

For those who are not familiar with railroad syntax diagrams, they show a
grammar's syntax using arrows and blocks, instead of BNF - here's an excerpt
from the Python grammar, plus "ASCII-art" diagrams - must be viewed in
non-prop font to be appreciated:

suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT

----+--> simple_stmt --------------------------------->\
    |                                                   |
    \--> NEWLINE --> INDENT --+--> stmt --+--> DEDENT --+-->
                             /            |
                             \----<-------/

if_stmt: 'if' test ':' suite ('elif' test ':' suite)* ['else' ':' suite]


--> 'if' -> test --> ':' --> suite -->+
                                      |
      ------------<-------------------+
     /
    +
    | ------------<------------------------
    |/                                     \
    +                                      |
    |                                      |
    +-> 'elif' -> test -> ':' --> suite -->/
    |
    |
    +-> 'else' -> ':' --> suite -->
    |                              \
    \---------------->--------------+------->


I was recently contacted by a volunteer in Banda Aceh teaching tsunami
refugees how to program in Python (new job skills and all that), and he
asked if there were any updated versions of these diagrams, or if it would
be difficult to generate them anew.   It seems that railroad diagrams are
nice and unambiguous for his students to use, in the face of verbal language
barriers.

I have written a pyparsing parser that reads the grammar file that ships
with Python - the parser is included in the latest release of pyparsing, and
also online at the pyparsing.wikispaces.com - but I have no graph-generating
tools to go the next step: generation of the railroad diagrams (in something
more legible/appealing than ASCII-art!).

Anyone interested in helping complete this last step?

Thanks,
-- Paul