spot/doc/org/tut21.org

# -*- coding: utf-8 -*-
#+TITLE: Custom print of an automaton
#+SETUPFILE: setup.org
#+HTML_LINK_UP: tut.html

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.

#+BEGIN_SRC sh :results verbatim :exports both
ltl2tgba 'Fa | G(Fb&Fc)' -H | tee tut21.hoa
#+END_SRC

#+RESULTS:
#+begin_example
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--
#+end_example

We now write some C++ to load this automaton [[file:tut20.org][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.

#+BEGIN_SRC C++ :results verbatim :exports both
  #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';
          }
      }
  }
#+END_SRC

#+RESULTS:
#+begin_example
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 = {}
#+end_example


#+BEGIN_SRC sh :results verbatim :exports none
rm -f tut21.hoa
#+END_SRC