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Custom print of an automaton

This example demonstrates how to iterate over an automaton. We will only show how to do this in C++: the Python bindings for the automata are not yet supporting these low-level iterations, and the shell commands aren't up to the task either.

First let's create an example automaton in HOA format.

ltl2tgba 'Fa | G(Fb&Fc)' -H | tee tut21.hoa
HOA: v1
name: "Fa | G(Fb & Fc)"
States: 4
Start: 0
AP: 3 "a" "b" "c"
acc-name: generalized-Buchi 2
Acceptance: 2 Inf(0)&Inf(1)
properties: trans-labels explicit-labels trans-acc complete
properties: stutter-invariant
--BODY--
State: 0
[0] 1
[!0] 2
[!0] 3
State: 1
[t] 1 {0 1}
State: 2
[0] 1
[!0] 2
State: 3
[1&2] 3 {0 1}
[1&!2] 3 {0}
[!1&2] 3 {1}
[!1&!2] 3
--END--

We now write some C++ to load this automaton as we did before, and in custom_print() we print it out in a custom way by explicitly iterating over it states and edges.

The only tricky part is to print the edge labels. Since they are BDDs, printing them directly would just show the number of BDD variables involved. Using bdd_print_formula and passing it the BDD dictionary associated to the automaton is the way to print the edge labels.

#include <string>
#include <iostream>
#include "parseaut/public.hh"
#include "twaalgos/hoa.hh"
#include "twa/bddprint.hh"

void custom_print(std::ostream& out, spot::twa_graph_ptr& aut);

int main()
{
  std::string input = "tut21.hoa";
  spot::parse_aut_error_list pel;
  spot::bdd_dict_ptr dict = spot::make_bdd_dict();
  spot::parsed_aut_ptr pa = parse_aut(input, pel, dict);
  if (spot::format_parse_aut_errors(std::cerr, input, pel))
    return 1;
  // This cannot occur when reading a never claim, but
  // it could while reading a HOA file.
  if (pa->aborted)
    {
      std::cerr << "--ABORT-- read\n";
      return 1;
    }
  custom_print(std::cout, pa->aut);
  return 0;
}

void custom_print(std::ostream& out, spot::twa_graph_ptr& aut)
{
  // Print some meta-data
  out << "Acceptance: " << aut->get_acceptance() << '\n';
  out << "Number of sets: " << aut->num_sets() << '\n';
  out << "Number of states: " << aut->num_states() << '\n';
  out << "Number of edges: " << aut->num_edges() << '\n';
  out << "Initial state: " << aut->get_init_state_number() << '\n';

  // We need the dictionary to print the BDD that labels the edge
  const auto& dict = aut->get_dict();

  // States are numbered from 0 to n-1
  unsigned n = aut->num_states();
  for (unsigned s = 0; s < n; ++s)
    {
      out << "State " << s << ":\n";

      // The out(s) method returns a fake container that can be
      // iterated over as if the contents was the edges going
      // out of s.  Each of these edge is a quadruplet
      // (src,dst,cond,acc).  Note that because this returns
      // a reference, the edge can also be modified.
      for (auto& t: aut->out(s))
        {
          out << "  edge(" << t.src << " -> " << t.dst << ")\n    label = ";
          spot::bdd_print_formula(out, dict, t.cond);
          out << "\n    acc sets = " << t.acc << '\n';
        }
    }
}
Acceptance: Inf(0)&Inf(1)
Number of sets: 2
Number of states: 4
Number of edges: 10
Initial state: 0
State 0:
  edge(0 -> 1)
    label = a
    acc sets = {}
  edge(0 -> 2)
    label = !a
    acc sets = {}
  edge(0 -> 3)
    label = !a
    acc sets = {}
State 1:
  edge(1 -> 1)
    label = 1
    acc sets = {0,1}
State 2:
  edge(2 -> 1)
    label = a
    acc sets = {}
  edge(2 -> 2)
    label = !a
    acc sets = {}
State 3:
  edge(3 -> 3)
    label = b & c
    acc sets = {0,1}
  edge(3 -> 3)
    label = b & !c
    acc sets = {0}
  edge(3 -> 3)
    label = !b & c
    acc sets = {1}
  edge(3 -> 3)
    label = !b & !c
    acc sets = {}

Author: root

Created: 2015-08-26 Wed 08:42

Emacs 24.4.1 (Org mode 8.2.10)

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