Verified Commit 6b1b2652 authored by Vladimír Štill's avatar Vladimír Štill
Browse files

CFG: Add a has_simple_rules function

parent 5cee58cd

grammars_cfg.py

+18 −5
Original line number Diff line number Diff line
@@ -326,14 +326,19 @@ class CFG: 
                       new_rules, new_init)

        return CFG(self.nonterminals, self.terminals, new_rules, self.init)



    def remove_simple_rules(self) -> CFG:

        simple_to: Dict[Nonterminal, Set[Nonterminal]] =\

            {n: {n} for n in self.nonterminals}

    def get_simple_to(self) -> Dict[Nonterminal, Set[Nonterminal]]:

        """

        Get a mapping from nonterminal to a set of nonterminals it can be

        *nontrivially* rewritten to (i.e., it does not include the nonterminal

        itself unless there is a rule of form X → X for it")

        """

        simple_to : Dict[Nonterminal, Set[Nonterminal]] \

            = {n: set() for n in self.nonterminals}



        for tracker in ChangeTracker():

            for src_orig in self.nonterminals:

                # make a copy to avoid error for changing during iteraton

                for src in list(simple_to[src_orig]):

                for src in list({src_orig} | simple_to[src_orig]):

                    for prod in self.rules.get(src, []):

                        if not isinstance(prod, Eps) and len(prod) == 1 \

                                and isinstance(prod[0], Nonterminal) \
@@ -341,9 +346,17 @@ class CFG: 
                            tracker.changed()

                            simple_to[src_orig].add(prod[0])



        return simple_to



    def has_simple_rules(self) -> bool:

        return any_of(lambda v: len(v) != 0, self.get_simple_to().values())



    def remove_simple_rules(self) -> CFG:

        simple_to = self.get_simple_to()



        new_rules: CFG.Rules = dict()

        for src in self.nonterminals:

            for esrc in simple_to[src]:

            for esrc in {src} | simple_to[src]:

                for prod in self.rules.get(esrc, []):

                    if len(prod) != 1 or typing.cast(CFG.Symbols, prod)[0] \

                            in self.terminals:

test_cfl_cfg.py

+17 −0
Original line number Diff line number Diff line
@@ -57,8 +57,10 @@ def test_remove_simple() -> None: 
                 C: {(a, a, C), (a, a)}},

                S)

    print(g)

    assert g.has_simple_rules()

    gs = g.remove_simple_rules()

    print(gs)

    assert not gs.has_simple_rules()

    assert (B, C) in gs.rules[gs.init]

    assert (a, B) in gs.rules[gs.init]

    assert (a,) in gs.rules[gs.init]
@@ -66,6 +68,21 @@ def test_remove_simple() -> None: 
    assert (a, a) in gs.rules[gs.init]





def test_remove_simple_2() -> None:

    g = cfl.CFG({S, A, B}, {a},

                {S: {(a, A)},

                 A: {(B,), (a, a)},

                 B: {(a,)}},

                S)

    print(g)

    assert g.has_simple_rules()

    gs = g.remove_simple_rules()

    print(gs)

    assert not gs.has_simple_rules()

    assert g.generates("aa")

    assert g.generates("aaa")





def test_is_epsilon_normal():

    assert g0.is_epsilon_normal_form()

    assert g1.is_epsilon_normal_form()