spot/doc/org/tut10.org

# -*- coding: utf-8 -*-
#+TITLE: Translating an LTL formula into a never claim
#+DESCRIPTION: Code example for translating formulas in Spot
#+INCLUDE: setup.org
#+HTML_LINK_UP: tut.html
#+PROPERTY: header-args:sh :results verbatim :exports both
#+PROPERTY: header-args:python :results output :exports both
#+PROPERTY: header-args:C+++ :results verbatim :exports both

Here is how to translate an LTL (or PSL) formula into a never claim.

* Shell

#+BEGIN_SRC sh
ltl2tgba --spin 'GFa -> GFb'
#+END_SRC

#+RESULTS:
#+begin_example
never { /* F(GFb | G!a) */
T0_init:
  if
  :: (true) -> goto T0_init
  :: (b) -> goto accept_S1
  :: (!(a)) -> goto accept_S2
  fi;
accept_S1:
  if
  :: (b) -> goto accept_S1
  :: (!(b)) -> goto T0_S3
  fi;
accept_S2:
  if
  :: (!(a)) -> goto accept_S2
  fi;
T0_S3:
  if
  :: (b) -> goto accept_S1
  :: (!(b)) -> goto T0_S3
  fi;
}
#+end_example

* Python

The =formula= function returns a formula object (or raises a
parse-error exception).  Formula objects have a =translate()= method
that returns an automaton, and the automata objects have a =to_str=
method that can output in one of the supported syntaxes.

So the translation is actually a one-liner in Python:

#+BEGIN_SRC python
import spot
print(spot.formula('GFa -> GFb').translate('BA').to_str('spin'))
#+END_SRC

#+RESULTS:
#+begin_example
never {
T0_init:
  if
  :: (true) -> goto T0_init
  :: (b) -> goto accept_S1
  :: (!(a)) -> goto accept_S2
  fi;
accept_S1:
  if
  :: (b) -> goto accept_S1
  :: (!(b)) -> goto T0_S3
  fi;
accept_S2:
  if
  :: (!(a)) -> goto accept_S2
  fi;
T0_S3:
  if
  :: (b) -> goto accept_S1
  :: (!(b)) -> goto T0_S3
  fi;
}

#+end_example

The above line can actually be made a bit shorter, because
=translate()= can also be used as a function (as opposed to a method)
that takes a formula (possibly as a string) as first argument:

#+BEGIN_SRC python
import spot
print(spot.translate('GFa -> GFb', 'buchi', 'sbacc').to_str('spin'))
#+END_SRC

#+RESULTS:
#+begin_example
never {
T0_init:
  if
  :: (true) -> goto T0_init
  :: (b) -> goto accept_S1
  :: (!(a)) -> goto accept_S2
  fi;
accept_S1:
  if
  :: (b) -> goto accept_S1
  :: (!(b)) -> goto T0_S3
  fi;
accept_S2:
  if
  :: (!(a)) -> goto accept_S2
  fi;
T0_S3:
  if
  :: (b) -> goto accept_S1
  :: (!(b)) -> goto T0_S3
  fi;
}

#+end_example

* C++

All the translation pipeline (this includes simplifying the formula,
translating the simplified formula into an automaton, and simplifying
the resulting automaton) is handled by the =spot::translator= class.
An instance of this class can configured by calling =set_type()= to
chose the type of automaton to output, =set_level()= to set the level
of optimization (it's high by default), and =set_pref()= to set
various preferences (like small or deterministic) or characteristic
(complete, unambiguous, state-based acceptance) for the resulting
automaton. Finally, the output as a never claim is done via the
=print_never_claim= function.

#+BEGIN_SRC C++
  #include <iostream>
  #include <spot/tl/parse.hh>
  #include <spot/twaalgos/translate.hh>
  #include <spot/twaalgos/neverclaim.hh>

  int main()
  {
    spot::parsed_formula pf = spot::parse_infix_psl("GFa -> GFb");
    if (pf.format_errors(std::cerr))
      return 1;
    spot::translator trans;
    trans.set_type(spot::postprocessor::Buchi);
    trans.set_pref(spot::postprocessor::SBAcc
                   | spot::postprocessor::Small);
    spot::twa_graph_ptr aut = trans.run(pf.f);
    print_never_claim(std::cout, aut) << '\n';
    return 0;
  }
#+END_SRC

#+RESULTS:
#+begin_example
never {
T0_init:
  if
  :: (true) -> goto T0_init
  :: (b) -> goto accept_S1
  :: (!(a)) -> goto accept_S2
  fi;
accept_S1:
  if
  :: (b) -> goto accept_S1
  :: (!(b)) -> goto T0_S3
  fi;
accept_S2:
  if
  :: (!(a)) -> goto accept_S2
  fi;
T0_S3:
  if
  :: (b) -> goto accept_S1
  :: (!(b)) -> goto T0_S3
  fi;
}

#+end_example

* Additional comments

The Python version of =translate()= is documented as follows:

#+BEGIN_SRC python :exports results
import spot
help(spot.translate)
#+END_SRC

#+RESULTS:
#+begin_example
Help on function translate in module spot:

translate(formula, *args, dict=<spot.impl.bdd_dict; proxy of <Swig Object of type 'std::shared_ptr< spot::bdd_dict > *' at 0x7f42f4cea030> >, xargs=None)
    Translate a formula into an automaton.

    Keep in mind that 'Deterministic' expresses just a preference that
    may not be satisfied.

    The optional arguments should be strings among the following:
    - at most one in 'GeneralizedBuchi', 'Buchi', or 'Monitor',
      'generic', 'parity', 'parity min odd', 'parity min even',
      'parity max odd', 'parity max even', 'coBuchi'
      (type of acceptance condition to build)
    - at most one in 'Small', 'Deterministic', 'Any'
      (preferred characteristics of the produced automaton)
    - at most one in 'Low', 'Medium', 'High'
      (optimization level)
    - any combination of 'Complete', 'Unambiguous',
      'StateBasedAcceptance' (or 'SBAcc' for short), and
      'Colored' (only for parity acceptance)

    The default corresponds to 'tgba', 'small' and 'high'.

    Additional options can be supplied using a `spot.option_map`, or a
    string (that will be converted to `spot.option_map`), as the `xargs`
    argument.  This is similar to the `-x` option of command-line tools;
    so check out the spot-x(7) man page for details.

#+end_example

#  LocalWords:  utf html args SRC tgba GFa GFb init fi str aut xargs
#  LocalWords:  coBuchi StateBasedAcceptance SBAcc