pyparsing: grammar for list of Dictionaries (erlang)

erlang, parsing, pyparsing, python

Solution

Ok, so I have never worked with pyparsing before, so excuse me if my solution does not make sense. Here we go:

As far as I understand what you need is three main structures. The most common mistake you made was grouping delimitedLists. They are already grouped, so you have an issue of double grouping. Here are my definitions:

for {a,"b"}:

erlangTaggedTuple = Dict(Group(Suppress('{') + erlangAtom + Suppress(',') + erlangValue + Suppress('}') ))

for [{a,"b"}, {c,"d"}]:

erlangDict = Suppress('[') + delimitedList( erlangTaggedTuple ) + Suppress(']')

for the rest:

erlangList <<= Suppress('[') + delimitedList( Group(erlangDict|erlangList) ) + Suppress(']')

So my fix for your code is:

#!/usr/bin/env python2.7

from pyparsing import *

# Erlang config file definition:
erlangAtom = Word( alphas + '_')
erlangString = dblQuotedString.setParseAction( removeQuotes )

erlangValue = Forward()
erlangList = Forward()

erlangTaggedTuple = Dict(Group(Suppress('{') + erlangAtom + Suppress(',') +
                           erlangValue + Suppress('}') ))
erlangDict = Suppress('[') + delimitedList( erlangTaggedTuple ) + Suppress(']') 
erlangList <<= Suppress('[') + delimitedList( Group(erlangDict|erlangList) ) + Suppress(']')

erlangValue <<= ( erlangAtom | erlangString |
                  erlangTaggedTuple |
                  erlangDict| erlangList )

if __name__ == "__main__":
    working = """
[{foo,"bar"}, {baz, "bar2"}]
"""

    broken = """
[
    [{foo,"bar"}, {baz, "bar2"}],
    [{foo,"bob"}, {baz, "fez"}]
]
"""
    w = erlangValue.parseString(working)
    print w.dump()

    b = erlangValue.parseString(broken)
    print "b[0]:", b[0].dump()
    print "b[1]:", b[1].dump()

Which gives the output:

[['foo', 'bar'], ['baz', 'bar2']]
- baz: bar2
- foo: bar
b[0]: [['foo', 'bar'], ['baz', 'bar2']]
- baz: bar2
- foo: bar
b[1]: [['foo', 'bob'], ['baz', 'fez']]
- baz: fez
- foo: bob

Hope that helps, cheers!

Problem

I'm trying to build a grammar to parse an Erlang tagged tuple list, and map this to a Dict in pyparsing. I'm having problems when I have a list of Dicts. The grammar works if the Dict has just one element, but when I add a second can't work out now to get it to parse. Current (simplified grammar code (I removed the bits of the language not necessary in this case): ``` #!/usr/bin/env python2.7 from pyparsing import * # Erlang config file definition: erlangAtom = Word( alphas + '_') erlangString = dblQuotedString.setParseAction( removeQuotes ) erlangValue = Forward() erlangList = Forward() erlangElements = delimitedList( erlangValue ) erlangCSList = Suppress('[') + erlangElements + Suppress(']') erlangList <<= Group( erlangCSList ) erlangTaggedTuple = Group( Suppress('{') + erlangAtom + Suppress(',') + erlangValue + Suppress('}') ) erlangDict = Dict( Suppress('[') + delimitedList( erlangTaggedTuple ) + Suppress(']') ) erlangValue <<= ( erlangAtom | erlangString | erlangTaggedTuple | erlangDict | erlangList ) if __name__ == "__main__": working = """ [{foo,"bar"}, {baz, "bar2"}] """ broken = """ [ [{foo,"bar"}, {baz, "bar2"}], [{foo,"bob"}, {baz, "fez"}] ] """ w = erlangValue.parseString(working) print w.dump() b = erlangValue.parseString(broken) print "b[0]:", b[0].dump() print "b[1]:", b[1].dump() ``` This gives: ``` [['foo', 'bar'], ['baz', 'bar2']] - baz: bar2 - foo: bar b[0]: [['foo', 'bar'], ['baz', 'bar2'], ['foo', 'bob'], ['baz', 'fez']] - baz: fez - foo: bob b[1]: Traceback (most recent call last): File "./erl_testcase.py", line 39, in <module> print "b[1]:", b[1].dump() File "/Library/Python/2.7/site-packages/pyparsing.py", line 317, in __getitem__ return self.__toklist[i] IndexError: list index out of range ``` i.e. `working` works, but `broken` doesn't parse as two lists. Any ideas? Edit: Tweaked testcase to be more explicit about expected output.

Original source