예제 #1
0
    def print_vars_and_trans(self, modelpath):
        fsm = BddFsm.from_filename(modelpath)
        self.assertIsNotNone(fsm)

        propDb = glob.prop_database()
        master = propDb.master

        print("MODEL:", modelpath)
        print("============================================================")

        sexpfsm_ptr = nsprop.Prop_get_scalar_sexp_fsm(master._ptr)
        var_list = nssexp.SexpFsm_get_vars_list(sexpfsm_ptr)

        var_list_length = nsutils.NodeList_get_length(var_list)
        print("var_list length:", var_list_length)

        var_list_iter = nsutils.NodeList_get_first_iter(var_list)
        while var_list_iter is not None:
            item = nsutils.NodeList_get_elem_at(var_list, var_list_iter)

            print(nsnode.sprint_node(item))
            print("--------------------------")

            var_init = nssexp.SexpFsm_get_var_init(sexpfsm_ptr, item)
            print(nsnode.sprint_node(var_init))

            print("--------------------------")

            var_trans = nssexp.SexpFsm_get_var_trans(sexpfsm_ptr, item)
            print(nsnode.sprint_node(var_trans))

            print("--------------------------")
            print()

            var_list_iter = nsutils.ListIter_get_next(var_list_iter)
예제 #2
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    def test_create_trans_counters_assign(self):

        fsm = self.model("tests/pynusmv/models/counters-assign.smv")

        c1c0bdd = evalSexp(fsm, "c1.c = 0")
        c2c0bdd = evalSexp(fsm, "c2.c = 0")
        c1c1bdd = evalSexp(fsm, "c1.c = 1")
        c2c1bdd = evalSexp(fsm, "c2.c = 1")

        self.assertEqual(c1c0bdd & c2c0bdd, fsm.init)
        self.assertEqual(c1c0bdd & c2c1bdd | c1c1bdd & c2c0bdd,
                         fsm.post(fsm.init))

        fsmbuilder = nscompile.Compile_get_global_fsm_builder()
        enc = nsenc.Enc_get_bdd_encoding()
        ddmanager = nsbddenc.BddEnc_get_dd_manager(enc)
        base_enc = nsbddenc.bddenc2baseenc(enc)
        symb_table = nsbaseenc.BaseEnc_get_symb_table(base_enc)

        propDb = glob.prop_database()
        master = propDb.master

        sexpfsm_ptr = nsprop.Prop_get_scalar_sexp_fsm(master._ptr)

        # Create a new expr trans
        c2c = self.get_variable_from_string(sexpfsm_ptr, "c2.c")
        self.assertIsNotNone(c2c)
        # trans = next(c2c) = (c2.c + 1) % 4
        nextc2c = nssexp.Expr_next(c2c, symb_table)
        one = nsnode.create_node(parser.NUMBER, None, None)
        one.left.nodetype = nsnode.int2node(1)
        self.assertEqual(nsnode.sprint_node(one), "1")
        four = nsnode.create_node(parser.NUMBER, None, None)
        four.left.nodetype = nsnode.int2node(4)
        self.assertEqual(nsnode.sprint_node(four), "4")
        c2cp1 = nssexp.Expr_plus(c2c, one)
        c2cp1m4 = nssexp.Expr_mod(c2cp1, four)
        trans = nssexp.Expr_equal(nextc2c, c2cp1m4, symb_table)

        clusters = nsfsm.FsmBuilder_clusterize_expr(fsmbuilder, enc, trans)
        cluster_options = nsbddtrans.ClusterOptions_create(
            nsopt.OptsHandler_get_instance())

        bddTrans = BddTrans(
            nsbddtrans.BddTrans_create(
                ddmanager, clusters, nsbddenc.BddEnc_get_state_vars_cube(enc),
                nsbddenc.BddEnc_get_input_vars_cube(enc),
                nsbddenc.BddEnc_get_next_state_vars_cube(enc),
                nsopt.get_partition_method(nsopt.OptsHandler_get_instance()),
                cluster_options))

        fsm.trans = bddTrans

        self.assertEqual(c1c0bdd & c2c0bdd, fsm.init)
        self.assertEqual(c2c1bdd, fsm.post(fsm.init))
    def test_get_instances_after_flattening(self):
        car = nsnode.car
        cdr = nsnode.cdr

        glob.load_from_file("tests/pynusmv_tools/ctlk/dining-crypto.smv")

        # Flatten
        glob.flatten_hierarchy()

        # Get parsed tree
        tree = nsparser.cvar.parsed_tree
        self.assertIsNotNone(tree)
        self.assertIsNotNone(car(tree))

        print(tree.type)  # 145 = CONS
        print(car(tree).type)  # 117 = MODULE
        print(nsnode.sprint_node(car(car(car(tree)))))  # main
        print(cdr(car(tree)).type)  # 145 = CONS
        print(car(cdr(car(tree))).type)  # 113 = DEFINE
        print(cdr(cdr(car(tree))))  # None
        print(cdr(tree).type)  # 145 = CONS
        print(car(cdr(tree)).type)  # 117 = MODULE
        print(nsnode.sprint_node(car(car(car(cdr(tree))))))  # cryptograph

        print("----- Instances after flattening")
        # main module is car(tree)
        main_vars = self.get_instances_for_module(car(tree))
        # Variables are removed from parsed_tree when flattening
        self.assertEqual(len(main_vars), 0)

        instances_args = {}

        for var in main_vars:
            # var = COLON(ATOM, MODTYPE(ATOM, CONS))

            varname = nsnode.sprint_node(car(var))
            instances_args[varname] = []

            args = cdr(cdr(var))
            argslist = []
            while args is not None:
                arg = car(args)
                instances_args[varname].append(arg)
                argslist.append(nsnode.sprint_node(arg))
                args = cdr(args)

            print(varname, ":", nsnode.sprint_node(car(cdr(var))), argslist)

        print("------------------------------------------------------")
예제 #4
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def _get_variables_by_instances(agents):
    """
    Return a dictionary of instance->list of variables
    """
    st = symb_table()
    flatHierarchy = nscompile.cvar.mainFlatHierarchy

    # Populate variables with instances
    variables = {}
    for agent in agents:
        variables[agent] = []

    varset = nscompile.FlatHierarchy_get_vars(flatHierarchy)
    varlist = nsset.Set_Set2List(varset)

    ite = nsutils.NodeList_get_first_iter(varlist)
    while not nsutils.ListIter_is_end(ite):
        var = nsutils.NodeList_get_elem_at(varlist, ite)
        varname = nsnode.sprint_node(var)
        isVar = nssymb_table.SymbTable_is_symbol_state_var(st._ptr, var)
        if isVar:
            # Put the var in the variables dictionary, under the right instance
            topcontext = varname.partition(".")[0]
            if topcontext in variables:
                variables[topcontext].append(var)
        ite = nsutils.ListIter_get_next(ite)

    return variables
예제 #5
0
파일: dd.py 프로젝트: yyaan/pynusmv
    def get_str_values(self, layers=None):
        """
        Return a dictionary of the (variable, value) pairs of these Inputs.

        :param layers: if not `None`, the set of names of the layers from which
                       picking the string values
        :rtype: a dictionary of pairs of strings.

        """
        enc = self._fsm.bddEnc
        # Get symb table from enc (BaseEnc)
        table = enc.symbTable

        # Get symbols (SymbTable) for inputs
        if layers is None:
            layers = nssymb_table.SymbTable_get_class_layer_names(
                table._ptr, None)
            symbols = nssymb_table.SymbTable_get_layers_i_symbols(
                table._ptr, layers)
            layers_array = None
        else:
            layers_array = nsutils.array_alloc_strings(len(layers))
            for i, layer in enumerate(layers):
                nsutils.array_insert_strings(layers_array, i, layer)
            symbols = nssymb_table.SymbTable_get_layers_i_symbols(
                table._ptr, layers_array)

        # Get assign symbols (BddEnc)
        assign_list = nsbddEnc.BddEnc_assign_symbols(enc._ptr, self._ptr,
                                                     symbols, 0, None)

        values = {}
        # Traverse the symbols to print variables of the state
        assign_list_ptr = assign_list
        while assign_list_ptr:
            assignment = nsnode.car(assign_list_ptr)
            var = nsnode.car(assignment)
            val = nsnode.cdr(assignment)
            values[nsnode.sprint_node(var)] = nsnode.sprint_node(val)
            assign_list_ptr = nsnode.cdr(assign_list_ptr)

        nsnode.free_list(assign_list)
        nsutils.NodeList_destroy(symbols)
        if layers_array:
            nsutils.array_free(layers_array)

        return values
    def test_printing_parsed_tree(self):
        car = nsnode.car
        cdr = nsnode.cdr

        glob.load_from_file("tests/pynusmv_tools/ctlk/dining-crypto.smv")

        # Get parsed tree
        tree = nsparser.cvar.parsed_tree

        print(tree.type)  # 145 = CONS
        print(car(tree).type)  # 117 = MODULE
        print(car(car(tree)).type)  # 119 = MODTYPE
        print(nsnode.sprint_node(car(car(car(tree)))))  # main
        print(cdr(tree).type)  # 145 = CONS
        print(car(cdr(tree)).type)  # 117 = MODULE
        print(car(car(car(cdr(tree)))).type)  # 161 = ATOM
        print(nsnode.sprint_node(car(car(car(cdr(tree))))))  # cryptograph
        print(cdr(cdr(tree)))  # None
예제 #7
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 def show_types(self, node, indent=""):
     if node is not None:
         if node.type not in {nsparser.NUMBER, nsparser.ATOM}:
             print(indent + str(node.type))
             self.show_types(nsnode.car(node), indent + " ")
             self.show_types(nsnode.cdr(node), indent + " ")
         else:
             print(indent + str(node.type), ":", nsnode.sprint_node(node))
     else:
         print(indent + "None")
예제 #8
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    def get_variable_from_string(self, sexpfsm_ptr, var_string):
        var_list = nssexp.SexpFsm_get_vars_list(sexpfsm_ptr)

        var_list_iter = nsutils.NodeList_get_first_iter(var_list)
        while var_list_iter is not None:
            var = nsutils.NodeList_get_elem_at(var_list, var_list_iter)

            if nsnode.sprint_node(var) == var_string:
                return var

            var_list_iter = nsutils.ListIter_get_next(var_list_iter)

        return None
예제 #9
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 def test_good_identifiers(self):
     exprs = ["a",
              "a[4]",
              "t[v.r]",
              "inn",
              "AA",
              "a.b"
             ]
     
     for expr in exprs:
         node = parse_identifier(expr)
         self.assertIsNotNone(node)
         self.assertIsNotNone(nsnode.sprint_node(node))
예제 #10
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 def test_good_simple_expressions(self):
     exprs = ["a.car = 3",
              "e <= 56",
              "a[4] & t[v]",
              "inn | outt -> TRUE",
              "AA + B = C - D",
              "a -- b = c" # OK because b = c is commented so the expr is 'a'
             ]
     
     for expr in exprs:
         node = parse_simple_expression(expr)
         self.assertIsNotNone(node)
         self.assertIsNotNone(nsnode.sprint_node(node))
예제 #11
0
파일: dd.py 프로젝트: yyaan/pynusmv
    def get_str_values(self):
        """
        Return a dictionary of the (variable, value) pairs of this StateInputs.

        :rtype: a dictionary of pairs of strings.

        """
        enc = self._fsm.bddEnc
        # Get symb table from enc (BaseEnc)
        table = enc.symbTable

        # Get symbols (SymbTable) for states
        layers = nssymb_table.SymbTable_get_class_layer_names(table._ptr, None)
        symbols = nssymb_table.SymbTable_get_layers_sf_symbols(
            table._ptr, layers)
        isymbols = nssymb_table.SymbTable_get_layers_i_symbols(
            table._ptr, layers)
        nsutils.NodeList_concat(symbols, isymbols)
        nsutils.NodeList_destroy(isymbols)

        # Get assign symbols (BddEnc)
        assign_list = nsbddEnc.BddEnc_assign_symbols(enc._ptr, self._ptr,
                                                     symbols, 0, None)

        values = {}
        # Traverse the symbols to print variables of the state
        assign_list_ptr = assign_list
        while assign_list_ptr:
            assignment = nsnode.car(assign_list_ptr)
            var = nsnode.car(assignment)
            val = nsnode.cdr(assignment)
            values[nsnode.sprint_node(var)] = nsnode.sprint_node(val)
            assign_list_ptr = nsnode.cdr(assign_list_ptr)

        nsnode.free_list(assign_list)

        nsutils.NodeList_destroy(symbols)

        return values
예제 #12
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 def test_good_next_expressions(self):
     exprs = ["next(a) = a",
              "e.ne <= next(53)",
              "a[4] & t[next(v)]",
              "inn | next(outt) -> TRUE",
              "AA + B = next(C) - D",
              "a -- b = init(c) % 5" # OK because b = init(c) % 5
                                     # is commented so the expr is 'a'
             ]
     
     for expr in exprs:
         node = parse_next_expression(expr)
         self.assertIsNotNone(node)
         self.assertIsNotNone(nsnode.sprint_node(node))
예제 #13
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    def print_transs(self, filepath):
        # Parse a model
        nsparser.ReadSMVFromFile(filepath)
        parsed_tree = nsparser.cvar.parsed_tree

        print("----------------------------------")
        print(filepath)
        print("----------------------------------")

        # Get the trans
        trs = self.transs(parsed_tree)
        for tr in trs:
            self.assertEqual(tr.type, nsparser.TRANS)

            print("----- TRANS ----------------------")
            print(nsnode.sprint_node(car(tr)))
예제 #14
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    def print_mainFlatHierarchy(self, filepath):
        fsm = self.model(filepath)

        flatHierarchy = nscompile.cvar.mainFlatHierarchy

        print("-------------------------------------------")
        print(filepath)
        print("-------------------------------------------")

        # VARS
        print("----- VARS --------------------------------")
        var_set = nscompile.FlatHierarchy_get_vars(flatHierarchy)
        ite = nsset.Set_GetFirstIter(var_set)
        while not nsset.Set_IsEndIter(ite):
            var = nsset.Set_GetMember(var_set, ite)
            print(nsnode.sprint_node(var))
            ite = nsset.Set_GetNextIter(ite)

        # INIT
        print("----- INIT --------------------------------")
        init = nscompile.FlatHierarchy_get_init(flatHierarchy)
        print(nsnode.sprint_node(init))

        # INPUT
        print("----- INPUT -------------------------------")
        inp = nscompile.FlatHierarchy_get_trans(flatHierarchy)
        print(nsnode.sprint_node(inp))

        # TRANS
        print("----- TRANS -------------------------------")
        trans = nscompile.FlatHierarchy_get_trans(flatHierarchy)
        print(nsnode.sprint_node(trans))

        # TRANS
        print("----- ASSIGN ------------------------------")
        assign = nscompile.FlatHierarchy_get_assign(flatHierarchy)
        # assign is a list of pairs <process-name, its-assignements>
        while assign is not None:
            pa_pair = car(assign)

            process = car(pa_pair)
            print("process:", nsnode.sprint_node(process))

            expr = cdr(pa_pair)
            print(nsnode.sprint_node(expr))

            assign = cdr(assign)
예제 #15
0
def _get_instances_args_for_module(modtree):
    """
    Return a dictionary of instance name -> list of instance arguments pairs,
    with instances of modules in module modtree.
    
    modtree is a part of the AST of the SMV model. modtree.type = MODULE
    """
    # MODULE(MODTYPE(...), declarationlist)
    varlist = {}

    declarations = nsnode.cdr(modtree)
    while declarations is not None:
        decl = nsnode.car(declarations)

        if decl.type == nsparser.VAR:

            decl = nsnode.car(decl)
            while decl is not None:
                var = nsnode.car(decl)
                # var_id : type => COLON(ATOM, type)
                if nsnode.cdr(var).type == nsparser.MODTYPE:
                    varid = nsnode.sprint_node(nsnode.car(var))
                    if varid in varlist:
                        pass  # TODO Variable already defined
                    else:
                        # Compute args list
                        argslist = []
                        args = nsnode.cdr(nsnode.cdr(var))
                        while args is not None:
                            arg = nsnode.car(args)
                            argslist.append(arg)
                            args = nsnode.cdr(args)
                        varlist[varid] = argslist
                decl = nsnode.cdr(decl)

        declarations = nsnode.cdr(declarations)

    return varlist
예제 #16
0
 def __repr__(self):
     return "WFF("+nsnode.sprint_node(self._ptr)+") for "+str(self._ptr)
예제 #17
0
 def __str__(self):
     return nsnode.sprint_node(self._ptr)
예제 #18
0
    def test_trans(self):
        # Parse a model
        #nsparser.ReadSMVFromFile("tests/pynusmv/models/modules.smv")
        #parsed_tree = nsparser.cvar.parsed_tree
        nscmd.Cmd_SecureCommandExecute(
            "read_model -i tests/pynusmv/models/modules.smv")
        nscmd.Cmd_SecureCommandExecute("flatten_hierarchy")

        st = nscompile.Compile_get_global_symb_table()

        #       main = nsnode.find_node(
        #               nsparser.ATOM,
        #               nsnode.string2node(nsutils.find_string("main")),
        #                None)
        #
        #       # Flatten
        #       nscompile.CompileFlatten_init_flattener()
        #       st = nscompile.Compile_get_global_symb_table()
        #       layer = nssymb_table.SymbTable_create_layer(st, "model",
        #                   nssymb_table.SYMB_LAYER_POS_BOTTOM)
        #       nssymb_table.SymbTable_layer_add_to_class(st, "model", "Model Class")
        #       nssymb_table.SymbTable_set_default_layers_class_name(st, "Model Class")
        #
        #       #hierarchy = nscompile.Compile_FlattenHierarchy(
        #       #                st, layer, main, None, None, 1, 0, None)
        #
        #       hierarchy = nscompile.FlatHierarchy_create(st)
        #       instances = nsutils.new_assoc()
        #
        #       nscompile.Compile_ConstructHierarchy(st, layer, main, None, None,
        #                       hierarchy, None, instances)
        #
        #       fhtrans = nscompile.FlatHierarchy_get_trans(hierarchy)
        #       print("NON FLATTENED")
        #       print(nsnode.sprint_node(fhtrans))
        #
        #       print(fhtrans.type)                 #169 = AND
        #       print(car(fhtrans))                 #None
        #       print(cdr(fhtrans).type)            #130 = CONTEXT
        #       print(car(cdr(fhtrans)).type)       #208 = DOT
        #       print(car(car(cdr(fhtrans))))       #None
        #       print(cdr(car(cdr(fhtrans))).type)  #161 = ATOM
        #       print(nsnode.sprint_node(cdr(car(cdr(fhtrans))))) #m
        #
        #       print(cdr(cdr(fhtrans)).type)       #192 = EQUAL
        #
        #
        #
        #       trans = nscompile.Compile_FlattenSexp(st, cdr(fhtrans), None)
        #       print("FLATTENED")
        #       print(nsnode.sprint_node(trans))

        layers = nssymb_table.SymbTable_get_class_layer_names(st, None)
        variables = nssymb_table.SymbTable_get_layers_sf_i_vars(st, layers)
        ite = nsutils.NodeList_get_first_iter(variables)
        while not nsutils.ListIter_is_end(ite):
            variable = nsutils.NodeList_get_elem_at(variables, ite)
            print(nsnode.sprint_node(variable))
            ite = nsutils.ListIter_get_next(ite)

        top = nsnode.find_node(nsparser.ATOM,
                               nsnode.string2node(nsutils.find_string("top")),
                               None)

        trans = nssexp.Expr_equal(nssexp.Expr_next(top, st), top, st)

        flattrans = nscompile.Compile_FlattenSexp(st, trans, None)

        inmod = nsnode.find_node(
            nsparser.ATOM, nsnode.string2node(nsutils.find_string("inmod")),
            None)

        t = nsnode.find_node(nsparser.ATOM,
                             nsnode.string2node(nsutils.find_string("t")),
                             None)

        m = nsnode.find_node(nsparser.ATOM,
                             nsnode.string2node(nsutils.find_string("m")),
                             None)

        my = nsnode.find_node(nsparser.ATOM,
                              nsnode.string2node(nsutils.find_string("my")),
                              None)

        n = nsnode.find_node(nsparser.ATOM,
                             nsnode.string2node(nsutils.find_string("n")),
                             None)

        mymod = nsnode.find_node(
            nsparser.ATOM, nsnode.string2node(nsutils.find_string("mymod")),
            None)

        main = nsnode.find_node(
            nsparser.ATOM, nsnode.string2node(nsutils.find_string("main")),
            None)

        minmod = nsnode.find_node(nsparser.DOT,
                                  nsnode.find_node(nsparser.DOT, None, m),
                                  inmod)

        ftrans = nssexp.Expr_equal(
            nssexp.Expr_next(inmod, st),
            nssexp.Expr_or(inmod, nsnode.find_node(nsparser.DOT, my, inmod)),
            st)
        print(nsnode.sprint_node(ftrans))

        res, err = nsparser.ReadNextExprFromString(
            "next(inmod) = (inmod | my.inmod) IN n")
        self.assertEqual(err, 0)
        trans = car(res)
        print(nsnode.sprint_node(trans))

        conttrans = nsnode.find_node(nsparser.CONTEXT,
                                     nsnode.find_node(nsparser.DOT, None, n),
                                     ftrans)
        print(nsnode.sprint_node(conttrans))

        fflattrans = nscompile.Compile_FlattenSexp(st, conttrans, None)
        flattrans = nscompile.Compile_FlattenSexp(st, trans, None)

        print(nsnode.sprint_node(fflattrans))
        print(nsnode.sprint_node(flattrans))
    def print_instances(self, filepath):
        print("----- Instances for", filepath)

        car = nsnode.car
        cdr = nsnode.cdr

        glob.load_from_file(filepath)

        # Get parsed tree
        tree = nsparser.cvar.parsed_tree

        print("--- Main instances")
        # main module is car(tree)
        main_vars = self.get_instances_for_module(car(tree))

        instances_args = {}

        for var in main_vars:
            # var = COLON(ATOM, MODTYPE(ATOM, CONS))

            varname = nsnode.sprint_node(car(var))
            instances_args[varname] = []

            args = cdr(cdr(var))
            argslist = []
            while args is not None:
                arg = car(args)
                instances_args[varname].append(arg)
                argslist.append(nsnode.sprint_node(arg))
                args = cdr(args)

            print(varname, ":", nsnode.sprint_node(car(cdr(var))), argslist)

        # Get FSM and stuff
        glob.compute_model()
        fsm = glob.prop_database().master.bddFsm
        self.assertIsNotNone(fsm)

        flatH = nscompile.cvar.mainFlatHierarchy
        st = nscompile.Compile_get_global_symb_table()
        self.assertIsNotNone(flatH)

        print("--- Check arguments instances")
        for instance in instances_args:
            print("INSTANCE", instance)
            for arg in instances_args[instance]:
                arg, err = nscompile.FlattenSexp(st, arg, None)
                self.assertEqual(err, 0)
                isVar = nssymb_table.SymbTable_is_symbol_var(st, arg)
                if isVar:
                    print("VAR", nsnode.sprint_node(arg))
                else:
                    print("NOT VAR", nsnode.sprint_node(arg))

        print("--- All vars")
        varset = nscompile.FlatHierarchy_get_vars(flatH)
        self.assertIsNotNone(varset)
        varlist = nsset.Set_Set2List(varset)
        self.assertIsNotNone(varlist)

        ite = nsutils.NodeList_get_first_iter(varlist)
        while not nsutils.ListIter_is_end(ite):
            var = nsutils.NodeList_get_elem_at(varlist, ite)
            isInput = nssymb_table.SymbTable_is_symbol_input_var(st, var)
            isVar = nssymb_table.SymbTable_is_symbol_var(st, var)
            if isInput:
                print("IVAR", "\t", "IN",
                      "'" + nsnode.sprint_node(car(var)) + "'", "\t",
                      nsnode.sprint_node(var))
            elif isVar:
                print("VAR", "\t", "IN",
                      "'" + nsnode.sprint_node(car(var)) + "'", "\t",
                      nsnode.sprint_node(var))
            else:
                print("[ERROR] Unknown type:", nsnode.sprint_node(var))
            ite = nsutils.ListIter_get_next(ite)

        print("------------------------------------------------------")
예제 #20
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파일: prop.py 프로젝트: yyaan/pynusmv
    def __str__(self):
        """
        Return a string representation of this specification.

        """
        return nsnode.sprint_node(self._ptr)
예제 #21
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def mas(agents=None, initial_ordering=None):
    """
    Return (and compute if needed) the multi-agent system represented by
    the currently read SMV model.
    
    If agents is not None, the set of agents (and groups) of the MAS is
    determined by agents.
    
    Otherwise, every top-level module instantiation is considered an agent
    where
        - her actions are the inputs variables prefixed by her name;
        - her observable variables are composed of
            * the state variables of the system prefixed by her name;
            * the state variables provided as an argument to the module
              instantiation.
    
    If initial_ordering is not None, it must be the path to a variables
    ordering file. It is used as the initial ordering for variables of the
    model.
    
    Note: if the MAS is already computed, agents and initial_ordering arguments
    have no effect.
    
    agents -- a set of agents.
    """
    global __mas
    if __mas is None:
        # Check cmps
        if not nscompile.cmp_struct_get_read_model(nscompile.cvar.cmps):
            raise NuSMVNoReadModelError("Cannot build MAS; no read file.")

        if agents is None:
            # Get agents names
            tree = nsparser.cvar.parsed_tree
            main = None
            while tree is not None:
                module = nsnode.car(tree)
                if (nsnode.sprint_node(nsnode.car(
                        nsnode.car(module))) == "main"):
                    main = module
                tree = nsnode.cdr(tree)
            if main is None:
                print("[ERROR] No main module.")
                return  # TODO Error, cannot find main module
            arguments = _get_instances_args_for_module(main)
            # arguments is a dict instancename(str)->listofargs(node)
            agents = arguments.keys()

            # Compute the model
            _compute_model(variables_ordering=initial_ordering)

            st = symb_table()

            # Flatten arguments and filter on variables
            argvars = _flatten_and_filter_variable_args(arguments)

            # Get agents observable variables (locals + module parameters)
            localvars = _get_variables_by_instances(agents)
            #localvars is a dict instancename(str)->listofvars(node)
            inputvars = _get_input_vars_by_instances(agents)

            # Merge instance variable arguments and local variables
            variables = {
                key: ((key in argvars and argvars[key] or []) +
                      (key in localvars and localvars[key] or []))
                for key in list(argvars.keys()) + list(localvars.keys())
            }

            # Compute epistemic relation
            singletrans = {}
            for agent in variables:
                transexpr = None
                for var in variables[agent]:
                    var = nsnode.sprint_node(var)
                    transexpr = nsnode.find_node(nsparser.AND,
                                                 _get_epistemic_trans(var),
                                                 transexpr)
                singletrans[agent] = transexpr

            # Process variables to get strings instead of nodes
            observedvars = {
                ag: {nsnode.sprint_node(v)
                     for v in variables[ag]}
                for ag in variables.keys()
            }
            inputvars = {
                ag: {nsnode.sprint_node(v)
                     for v in inputvars[ag]}
                for ag in inputvars.keys()
            }
            groups = None

        else:
            _compute_model(variables_ordering=initial_ordering)
            # observedvars: a dictionary of agent name -> set of observed vars
            observedvars = {
                str(agent.name): [str(var) for var in agent.observables]
                for agent in agents
            }
            # inputsvars: a dictionary of agent name -> set of inputs vars
            inputvars = {
                str(agent.name): [str(ivar) for ivar in agent.actions]
                for agent in agents
            }
            # groups:
            # a dictionary of group name -> names of agents of the group
            groups = {
                str(group.name): [str(agent.name) for agent in group.agents]
                for group in agents if isinstance(group, Group)
            }
            # singletrans: a dictionary of agent name -> epistemic transition
            singletrans = {}
            for agent in agents:
                name = str(agent.name)
                transexpr = None
                for var in observedvars[name]:
                    transexpr = nsnode.find_node(nsparser.AND,
                                                 _get_epistemic_trans(var),
                                                 transexpr)
                singletrans[name] = transexpr

        # Create the MAS
        fsm = _prop_database().master.bddFsm
        __mas = MAS(fsm._ptr,
                    observedvars,
                    inputvars,
                    singletrans,
                    groups=groups,
                    freeit=False)

    return __mas