Home Original page

Is pyparsing really a recursive descent parser?

Just Another Victim of the Ambient Morality ihatespam at hotmail.com
Wed Nov 7 14:51:34 EST 2007 
"Neil Cerutti" <horpner at yahoo.com> wrote in message 
news:slrnfj13e4.1hc.horpner at FIAD06.norwich.edu...
> On 2007-11-05, Just Another Victim of the Ambient Morality
> <ihatespam at hotmail.com> wrote:
>> "Kay Schluehr" <kay.schluehr at gmx.net> wrote in message
>> news:1194223837.104424.242360 at o3g2000hsb.googlegroups.com...
>>> I'm not sure one needs to start again with a naive approach
>>> just to avoid any parser theory. For a user of a parser it is
>>> quite important whether she has to wait 50 seconds for a parse
>>> to run or 50 milliseconds. I don't like to compromise speed
>>> for implementation simplicity here.
>>
>>     This attitude is all too prevalent among computer
>> professionals...  Of course it's a useful thing to shield users
>> from the intricacies of parser theory!  Just as much as it is
>> useful to shield drivers from needing automotive engineering or
>> software users from programing.  How many people have come to
>> this newsgroup asking about anomalous pyparsing behaviour,
>> despite their grammars being mathematically correct.
>
> You might be interested in the Early parsing algorithm. It is
> more efficient than the naive approach used in your prototype,
> and still handles ambiguous grammars.

    I think I might be interested in this algorithm, thank you!


> There is a Python module SPARK that provides generic classes for
> building small language compilers using an Early parser, and I
> was able to get it to parse your ambiguous grammar without
> trouble. It is not as convenient or as well documented as
> PyParsing, but the parsing algorithm provides the power you're
> looking for. It might serve as a backend for the library you're
> currently working on.
>
> http://www.cpsc.ucalgary.ca/~aycock/spark/

    You know, I tried this thing but, for the life of me, I can't figure out 
how to use it and the few tutorials out there are less than illuminating...
More information about the Python-list mailing list