def cfg_to_text(cfg: CFG) -> str:
"""Turns a context-free grammar [1]_
into its text representation.
Parameters
----------
cfg : CFG
Context-free grammar.
Examples
--------
>>> import cfpq_data
>>> cfg = cfpq_data.cfg_from_text("S -> a S b S")
>>> cfpq_data.cfg_to_text(cfg)
'S -> a S b S\\n'
Returns
-------
text : str
Context-free grammar
text representation.
References
----------
.. [1] https://en.wikipedia.org/wiki/Context-free_grammar#Formal_definitions
"""
return cfg.to_text()
def change_terminals_in_cfg(cfg: CFG, spec: Dict[str, str]) -> CFG:
"""Change terminals of
a context-free grammar [1]_.
Parameters
----------
cfg : CFG
Context-free grammar.
spec: Dict
Terminals mapping.
Examples
--------
>>> import cfpq_data
>>> cfg = cfpq_data.cfg_from_text("S -> a S b S")
>>> new_cfg = cfpq_data.change_terminals_in_cfg(cfg, {"a": "b", "b": "c"})
>>> new_cfg.to_text()
'S -> b S c S\\n'
Returns
-------
cfg : CFG
Context-free grammar with changed terminals.
References
----------
.. [1] https://en.wikipedia.org/wiki/Context-free_grammar#Formal_definitions
"""
regex = re.compile("|".join(map(re.escape, spec.keys())))
text = regex.sub(lambda match: spec[match.group(0)], cfg.to_text())
return cfg_from_text(text)
def from_cfg(cls, cfg: CFG):
"""
Build RSA from a given cfpq_data context-free grammar
@param cfg: CFG on which RSA is built
@return: initialized class
"""
grammar = cfg.to_text()
productions = dict()
for line in grammar.split("\n")[:-1]:
part_line = line.split(" -> ")
right = part_line[1]
if right == "":
right = "epsilon"
if part_line[0] in productions:
productions[part_line[0]] += " | " + right
else:
productions[part_line[0]] = right
grammar_new = ""
for nonterminal in productions:
grammar_new += nonterminal + " -> " + productions[nonterminal] + "\n"
grammar_new = grammar_new[:-1]
return RecursiveAutomaton.from_rsm(rsm_from_text(grammar_new))
def cfg_from_cnf(cnf: CFG) -> CFG:
"""Create a context-free grammar [2]_
from given context-free grammar
in Chomsky normal form [1]_.
Parameters
----------
cnf : CFG
Context free grammar
in Chomsky normal form.
Examples
--------
>>> import cfpq_data
>>> cnf = cfpq_data.cnf_from_text("S -> a S b S | epsilon")
>>> cfg = cfpq_data.cfg_from_cnf(cnf)
>>> [cfg.contains(word) for word in ["", "ab", "aabb"]]
[True, True, True]
Returns
-------
cfg : CFG
Context-free grammar.
References
----------
.. [1] https://en.wikipedia.org/wiki/Chomsky_normal_form
.. [2] https://en.wikipedia.org/wiki/Context-free_grammar#Formal_definitions
"""
return CFG.from_text(cnf.to_text(), cnf.start_symbol)
def rsm_from_cnf(cnf: CFG) -> RSM:
"""Create a Recursive State Machine [2]_
from context-free grammar
in Chomsky normal form [1]_.
Parameters
----------
cnf : CFG
Context-free grammar
in Chomsky normal form.
Examples
--------
>>> import cfpq_data
>>> cnf = cfpq_data.cnf_from_text("S -> a S b S | epsilon")
>>> rsm = cfpq_data.rsm_from_cnf(cnf)
>>> [rsm.contains(word) for word in ["", "ab", "aabb"]]
[True, True, True]
Returns
-------
rsm : RSM
Recursive State Machine.
References
----------
.. [1] https://en.wikipedia.org/wiki/Chomsky_normal_form
.. [2] Alur R., Etessami K., Yannakakis M. (2001) Analysis of Recursive State Machines. In: Berry G.,
Comon H., Finkel A. (eds) Computer Aided Verification. CAV 2001.
Lecture Notes in Computer Science, vol 2102.
Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-44585-4_18
"""
return rsm_from_text(cnf.to_text(), cnf.start_symbol)
def cnf_to_text(cnf: CFG) -> str:
"""Turns a context-free grammar
in Chomsky normal form [1]_
into its text representation.
Parameters
----------
cnf : CFG
Context-free grammar
in Chomsky normal form.
Examples
--------
>>> import cfpq_data
>>> cnf = cfpq_data.cnf_from_text("S -> a")
>>> cfpq_data.cnf_to_text(cnf)
'S -> a\\n'
Returns
-------
text : str
Context-free grammar
in Chomsky normal form
text representation.
References
----------
.. [1] https://en.wikipedia.org/wiki/Chomsky_normal_form
"""
return cnf.to_text()
def from_cfg(cls, cfg: CFG):
""" Create a recursive automaton from context-free grammar
Parameters
-----------
cfg : :class:`~pyformlang.cfg.CFG`
The context-free grammar
Returns
-----------
rsa : :class:`~pyformlang.rsa.RecursiveAutomaton`
The new recursive automaton built from context-free grammar
"""
initial_label = to_symbol(cfg.start_symbol)
grammar_in_true_format = remove_repetition_of_nonterminals_from_productions(
cfg.to_text())
boxes = set()
labels = set()
notation_for_epsilon = Epsilon().to_text()
for production in grammar_in_true_format.splitlines():
head, body = production.split(" -> ")
labels.add(to_symbol(head))
if body == "":
body = notation_for_epsilon
boxes.add(
Box(Regex(body).to_epsilon_nfa().minimize(), to_symbol(head)))
return RecursiveAutomaton(labels, initial_label, boxes)
def change_terminals_in_cnf(cnf: CFG, spec: Dict[str, str]) -> CFG:
"""Change terminals of
a context-free grammar [1]_
in Chomsky normal form.
Parameters
----------
cnf : CFG
Context-free grammar
in Chomsky normal form.
spec: Dict
Terminals mapping.
Examples
--------
>>> import cfpq_data
>>> cnf = cfpq_data.cnf_from_text("S -> a S b S | epsilon")
>>> new_cnf = cfpq_data.change_terminals_in_cnf(cnf, {"a": "b", "b": "c"})
>>> [new_cnf.contains(word) for word in ["", "bc", "bbcc"]]
[True, True, True]
Returns
-------
cnf : CFG
Context-free grammar
in Chomsky normal form
with changed terminals.
References
----------
.. [1] https://en.wikipedia.org/wiki/Chomsky_normal_form
"""
regex = re.compile("|".join(map(re.escape, spec.keys())))
text = regex.sub(lambda match: spec[match.group(0)], cnf.to_text())
return cnf_from_text(text)
