Re: [Pyparsing] results typing

[Paul M. <pt...@au...>]

Denis -

Thanks for your contributions on this list - please don't be discouraged if
you don't get many replies to your messages.  The readers here are mostly
lurkers (not that there's anything wrong with that!), or folks who post with
particular questions they need answered.  I too look at the list as
something of an archive of past pyparsing discussions.

I've had a chance to look over your notes in brief, but I really want to
give them more thought and consideration than I can spare just now.  In
general, I would say that the best way to start prototyping the integration
of your ideas with pyparsing as it exists is through parse actions (for
embellishing parse results) and helper methods (to simplify the construction
of expressions, or linking them to parse actions).

Whatever you do, I *strongly* suggest that you make these enhancements under
the control of the developer, and not automatically applied across the
board.  Pyparsing creates many intermediate parse expressions when building
the grammar, and parse results when parsing the source text, many of which
get either discarded or absorbed into a larger expressions.  Also, if your
enhancements stay in the realm of extensions that users may add or not of
their own choosing, then forward compatibility of existing code will be
preserved, and it will be easier to add your ideas to the core pyparsing
code.

Here is one idea that might address your question about linking results to
the original pyparsing expression (untested):

from pyparsing import *

def linkToResults(expr):
    def parseAction(tokens):
        tokens["expr"] = expr
    expr.addParseAction(parseAction)

integer = Word(nums).setName("integer")
decimal		= Combine(integer("int_part") + '.' + integer("dec_part"))
linkToResults(decimal)

print decimal.parseString("3.14159").dump()

Which prints:
['3.14159']
- dec_part: 14159
- expr: Combine:({integer "." integer})
- int_part: 3

Now the parse results that get created by expr will contain an added field
named "expr" that points back to the original expression (as shown by the
dump() output).  If this works well as a prototype, then it may be just as
easy to add it as a member function of ParserElement, so that any expression
can get linked back to from its results.

-- Paul