Optimistic apply method hits wall and can't tell ignorant developer why his grammar is wrong

[cratuki]

I'm reporting this bug in a form that's very specific to my case, but part of the reason I need to is because the library isn't giving me any feedback about what I'm doing wrong.

This is an example of the syntax, grammar and fail case I'm experiencing:
# --------------------------------------------------------
# START of code
# --------------------------------------------------------
from pymeta.grammar import OMeta

#
# Dictionary object in this namspace that our parsing
# actions will be able to affect
d_store = {}

#
# allows us to create the commands we want access to in a dict.
def cmd_dict(d_store):
    """Declares a bunch of functions in d_store and then
    returns it. Note that the functions may choose to
    affect d_store as they run, also."""

    def call(fn_name, **rest):
        d_store[fn_name](*rest)
        return fn_name

    def log(msg):
        print msg
    d_store['log'] = log

    def tok_chr(a):
        print 'hi, %s!'%a
        call('inc_count')
        return a
    d_store['tok_chr'] = tok_chr

    d_store['count'] = 0
    def inc_count():
        d_store['count'] += 1
    d_store['inc_count'] = inc_count

    return d_store
nspace = cmd_dict(d_store)

#
# Create the (likely flawed) grammar
grammar="""
begin ::= '[' <sketch_rest>
sketch_rest ::= ']' | ( ~(']') <sketch_entry> )*
sketch_entry ::= '(' <delimited_string>:key ',' <delimited_string>:val ')' => log('%s:%s'%(key, val))
delimited_string ::= (<dqstring> | <sqstring>)
dqstring ::= <token '"'> (<escapedChar> | ~('"') <anything>)* <token '"'>
sqstring ::= <token '\''> (<escapedChar> | ~('\'') <anything>)* <token '\''>

escapedChar ::= '\\' ('n' => "\n"
                     |'r' => "\r"
                     |'t' => "\t"
                     |'b' => "\b"
                     |'f' => "\f"
                     |'"' => '"'
                     |'\'' => "'"
                     |'\\' => "\\")

ws ::= ' ' | '\t' | '\n'
ws1 ::= <ws>+:s
ws0 ::= <ws>*:s
"""
g_ob = OMeta.makeGrammar(grammar, nspace, name="Sketch_Grammar")

#
# Feed in the sketch
sketch="[('p', 'Watch these'), ('q', 'And these')]"
g = g_ob(sketch)

#
# Fails here
res_apply = g.apply('begin')
# --------------------------------------------------------
# END of code
# --------------------------------------------------------

The error I get back is this:
$ python test.py
Traceback (most recent call last):
  File "test.py", line 60, in <module>
    g_ob = OMeta.makeGrammar(grammar, nspace, name="Sketch_Grammar")
  File "/usr/lib/python2.5/site-packages/pymeta/grammar.py", line 25, in makeGrammar
    return g.parseGrammar(name, PythonBuilder, cls, globals)
  File "/usr/lib/python2.5/site-packages/pymeta/grammar.py", line 120, in parseGrammar
    res = self.apply("grammar")
  File "/usr/lib/python2.5/site-packages/pymeta/runtime.py", line 168, in apply
    return self._apply(r, ruleName, args)
  File "/usr/lib/python2.5/site-packages/pymeta/runtime.py", line 195, in _apply
    [rule(), self.input])
  File "/pymeta_generated_code/pymeta_grammar__Grammar.py", line 352, in rule_grammar
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.5/site-packages/pymeta/builder.py", line 384, in makeGrammar
    code = compile(source, filename, "exec")
  File "/pymeta_generated_code/pymeta_grammar__Sketch_Grammar.py", line 66
    return self.locals['sqstring'] = _locals
                                   ^
SyntaxError: invalid syntax
$

I completely expect it's because I've done something wrong, but the break is very opaque because of the way pymeta dies.