Paul McGuire wrote:
> For instance, Seo Sanghyeon (I believe the same one now working on
> IronPython) uses the following technique in the EBNF parser/"compiler"
> that he contributed to the pyparsing examples directory:
>
> # list of all the grammar variable names
> all_names = '''
> integer
> meta_identifier
> terminal_string
> ...
> '''.split()
>
> # parse actions follow
> def do_integer(str, loc, toks):
> return int(toks[0])
FWIW, I find that my actions never use anything but the token list, so
to avoid writing a bunch of functions like the one above, I typically
write::
class ParseAction(object):
def __init__(self, func):
self.func = func
def __call__(self, string, index, tokens):
return self.func(*tokens)
...
# parse an integer
integer.addParseAction(ParseAction(int))
...
# parse a relation object, passing appropriate strings
# (or parsed objects) to the constructor
relation.setParseAction(ParseAction(Relation))
I guess the integer/int and relation/Relation is a little redundant, but
it's never bothered me too much.
STeVe
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