Editing automata

Vcsn provides different means to enter automata. One, which also applies to plain Python, is using the automaton constructor:

In [1]: 
import vcsn
vcsn.automaton('''
context = "lal_char(ab), z
$ -> 0 <2>
0 -> 1 <3>a,<4>b
1 -> 1 a
1 -> $
''', 'daut')
Out[1]:
%3 I0 0 0 I0->0 ⟨2⟩ F1 1 1 0->1 ⟨3⟩a, ⟨4⟩b 1->F1 1->1 a

See the documentation of vcsn.automaton for more details about this function. The syntax used to define the automaton is, however, described here.

In order to facilitate the definition of automata, Vcsn provides additional ''magic commands'' to the IPython Notebook. We will see through this guide how use this command.

%%automaton: Entering an Automaton

IPython supports so-called "cell magic-commands", that start with %%. Vcsn provides the %%automaton to enter the literal description of an automaton. For instance, the automaton above can enter as follows:

In [2]: 
%%automaton a
context = "lal_char(ab), z
$ -> 0 <2>
0 -> 1 <3>a,<4>b
1 -> 1 a
1 -> $
%3 I0 0 0 I0->0 ⟨2⟩ F1 1 1 0->1 ⟨3⟩a, ⟨4⟩b 1->F1 1->1 a

The first argument, here a, is the name of the variable in which this automaton is stored:

In [3]: 
a
Out[3]:
%3 I0 0 0 I0->0 ⟨2⟩ F1 1 1 0->1 ⟨3⟩a, ⟨4⟩b 1->F1 1->1 a

The second argument specifies the format in which the automaton is described, defaulting to daut:

In [4]: 
%%automaton a dot
digraph
{
  vcsn_context = "lal_char(ab), z"
  I -> 0 [label = "<2>"]
  0 -> 1 [label = "<3>a,<4>b"]
  1 -> 1 [label = a]
  1 -> F
}
%3 I0 0 0 I0->0 ⟨2⟩ F1 1 1 0->1 ⟨3⟩a, ⟨4⟩b 1->F1 1->1 a

The definition of automata entered this way are persistent: they are stored in the notebook and will be recovered when the page is reopened.

%automaton: Text-Based Edition of an Automaton

In IPython "line magic commands" begin with a single %. The line magic %automaton takes three arguments:

  1. the name of the automaton
  2. the format you want the textual description of the automaton. Defaults to daut.
  3. the display mode: h for horizontal and v for vertical. Defaults to h.

Contrary to the cell magic, the %automaton can be used to update an existing automaton:

In [5]: 
%automaton a

The real added value is that now you can interactively edit this automaton: changes in the text are immediately propagated on the rendered automaton.

When given a fresh variable name, %automaton creates a dummy automaton that you can use as a starting point:

In [6]: 
%automaton b fado

Beware however that these automata are not persistent: changes will be lost when the notebook is closed.

Automata Formats

Vcsn supports differents input and output formats. Some, such as tikz, are only export-only formats: they cannot be read by Vcsn.

daut

This simple format is work in progress: its precise syntax is still subject to changes. It is roughly a simplification of the dot syntax.

dot

This format relies on the "dot" language of the GraphViz toolkit (http://graphviz.org).

fado

This is the native language of the FAdo platform (http://fado.dcc.fc.up.pt).

efsm

This format is designed to support import/export with OpenFST (http://openfst.org): it wraps its multi-file format (one file describes the automaton with numbers as transition labels, and one or several others define these labels) into a single format. It is not designed to be used by humans, but rather to be handled by two tools:

  • efstcompile to compile such a file into the OpenFST binary file format,
  • efstdecompile to extract an efsm file from a binary OpenFST file.

grail

This format is made to exchange automata with the Grail (http://grailplus.org).