### 27.2 Writing a new module ¶

This section gives a simple example of writing a new module. showing the basic steps that must be done to create and add a new module that is available for the rest of the system to use. Note many things can be done solely in Scheme now and really only low-level very intensive things (like waveform synthesizers) need be coded in C++.

#### 27.2.1 Example 1: adding new modules ¶

The example here is a duration module which sets durations of phones for a given list of averages. To make this example more interesting, all durations in accented syllables are increased by 1.5. Note that this is just an example for the sake of one, this (and much better techniques) could easily done within the system as it is at present using a hand-crafted CART tree.

Our knew module, called `Duration_Simple` can most easily be added to the `./src/Duration/` directory in a file `simdur.cc`. You can worry about the copyright notice, but after that you’ll probably need the following includes

    #include <festival.h>

The module itself must be declared in a fixed form. That is receiving a single LISP form (an utterance) as an argument and returning that LISP form at the end. Thus our definition will start

    LISP FT_Duration_Simple(LISP utt)
    {

Next we need to declare an utterance structure and extract it from the LISP form. We also make a few other variable declarations

        EST_Utterance *u = get_c_utt(utt);
        EST_Item *s;
        float end=0.0, dur;
        LISP ph_avgs,ldur;

We cannot list the average durations for each phone in the source code as we cannot tell which phoneset we are using (or what modifications we want to make to durations between speakers). Therefore the phone and average duration information is held in a Scheme variable for easy setting at run time. To use the information in our C++ domain we must get that value from the Scheme domain. This is done with the following statement.

        ph_avgs = siod_get_lval("phoneme_averages","no phoneme durations");

The first argument to `siod_get_lval` is the Scheme name of a variable which has been set to an assoc list of phone and average duration before this module is called. See the variable `phone_durations` in `lib/mrpa_durs.scm` for the format. The second argument to `siod_get_lval`. is an error message to be printed if the variable `phone_averages` is not set. If the second argument to `siod_get_lval` is `NULL` then no error is given and if the variable is unset this function simply returns the Scheme value `nil`.

Now that we have the duration data we can go through each segment in the utterance and add the duration. The loop looks like

        for (s=u->relation("Segment")->head(); s != 0; s = next(s))
        {

We can lookup the average duration of the current segment name using the function `siod_assoc_str`. As arguments, it takes the segment name `s->name()` and the assoc list of phones and duration.

            ldur = siod_assoc_str(s->name(),ph_avgs);

Note the return value is actually a LISP pair (phone name and duration), or `nil` if the phone isn’t in the list. Here we check if the segment is in the list. If it is not we print an error and set the duration to 100 ms, if it is in the list the floating point number is extracted from the LISP pair.

            if (ldur == NIL)
            {
                cerr << "Phoneme: " << s->name() << " no duration "
                    << endl;
                dur = 0.100;
            }
            else
                dur = get_c_float(car(cdr(ldur)));

If this phone is in an accented syllable we wish to increase its duration by a factor of 1.5. To find out if it is accented we use the feature system to find the syllable this phone is part of and find out if that syllable is accented.

            if (ffeature(s,"R:SylStructure.parent.accented") == 1)
                dur *= 1.5;

Now that we have the desired duration we increment the `end` duration with our predicted duration for this segment and set the end of the current segment.

            end += dur;
            s->fset("end",end);
        }

Finally we return the utterance from the function.

        return utt;
    }

Once a module is defined it must be declared to the system so it may be called. To do this one must call the function `festival_def_utt_module` which takes a LISP name, the C++ function name and a documentation string describing what the module does. This will automatically be available at run-time and added to the manual. The call to this function should be added to the initialization function in the directory you are adding the module too. The function is called `festival_DIRNAME_init()`. If one doesn’t exist you’ll need to create it.

In `./src/Duration/` the function `festival_Duration_init()` is at the end of the file `dur_aux.cc`. Thus we can add our new modules declaration at the end of that function. But first we must declare the C++ function in that file. Thus above that function we would add

    LISP FT_Duration_Simple(LISP args);

While at the end of the function `festival_Duration_init()` we would add

       festival_def_utt_module("Duration_Simple",FT_Duration_Simple,
       "(Duration_Simple UTT)\n\
      Label all segments with average duration ... ");

In order for our new file to be compiled we must add it to the `Makefile` in that directory, to the `SRCS` variable. Then when we type `make` in `./src/` our new module will be properly linked in and available for use.

Of course we are not quite finished. We still have to say when our new duration module should be called. When we set

       (Parameter.set 'Duration_Method Duration_Simple)

for a voice it will use our new module, calls to the function `utt.synth` will use our new duration module.

Note in earlier versions of Festival it was necessary to modify the duration calling function in `lib/duration.scm` but that is no longer necessary.

#### 27.2.2 Example 2: accessing the utterance ¶

In this example we will make more direct use of the utterance structure, showing the gory details of following relations in an utterance. This time we will create a module that will name all syllables with a concatenation of the names of the segments they are related to.

As before we need the same standard includes

    #include "festival.h"

Now the definition the function

    LISP FT_Name_Syls(LISP utt)
    {

As with the previous example we are called with an utterance LISP object and will return the same. The first task is to extract the utterance object from the LISP object.

        EST_Utterance *u = get_c_utt(utt);
        EST_Item *syl,*seg;

Now for each syllable in the utterance we want to find which segments are related to it.

        for (syl=u->relation("Syllable")->head(); syl != 0; syl = next(syl))
        {

Here we declare a variable to cummulate the names of the segments.

            EST_String sylname = "";

Now we iterate through the `SylStructure` daughters of the syllable. These will be the segments in that syllable.

            for (seg=daughter1(syl,"SylStructure"); seg; seg=next(seg))
                sylname += seg->name();

Finally we set the syllables name to the concatenative name, and loop to the next syllable.

            syl->set_name(sylname);
        }

Finally we return the LISP form of the utterance.

        return utt;
    }

#### 27.2.3 Example 3: adding new directories ¶

In this example we will add a whole new subsystem. This will often be a common way for people to use Festival. For example let us assume we wish to add a formant waveform synthesizer (e.g like that in the free `rsynth` program). In this case we will add a whole new sub-directory to the modules directory. Let us call it `rsynth/`.

In the directory we need a `Makefile` of the standard form so we should copy one from one of the other directories, e.g. `Intonation/`. Standard methods are used to identify the source code files in a `Makefile` so that the `.o` files are properly added to the library. Following the other examples will ensure your code is integrated properly.

We’ll just skip over the bit where you extract the information from the utterance structure and synthesize the waveform (see `donovan/donovan.cc` or `diphone/diphone.cc` for examples).

To get Festival to use your new module you must tell it to compile the directory’s contents. This is done in `festival/config/config`. Add the line

    ALSO_INCLUDE += rsynth

to the end of that file (there are simialr ones mentioned). Simply adding the name of the directory here will add that as a new module and the directory will be compiled.

What you must provide in your code is a function `festival_DIRNAME_init()` which will be called at initialization time. In this function you should call any further initialization require and define and new Lisp functions you with to made available to the rest of the system. For example in the `rsynth` case we would define in some file in `rsynth/`

    #include "festival.h"

    static LISP utt_rtsynth(LISP utt)
    {
        EST_Utterance *u = get_c_utt(utt);
        // Do format synthesis
        return utt;
    }

    void festival_rsynth_init()
    {
       proclaim_module("rsynth");

       festival_def_utt_module("Rsynth_Synth",utt_rsynth,
       "(Rsynth_Synth UTT)
       A simple formant synthesizer");

       ...
    }

Integration of the code in optional (and standard directories) is done by automatically creating `src/modules/init_modules.cc` for the list of standard directories plus those defined as `ALSO_INCLUDE`. A call to a function called `festival_DIRNAME_init()` will be made.

This mechanism is specifically designed so you can add modules to the system without changing anything in the standard distribution.

#### 27.2.4 Example 4: adding new LISP objects ¶

This third example shows you how to add a new Object to Scheme and add wraparounds to allow manipulation within the Scheme (and C++) domain.

Like example 2 we are assuming this is done in a new directory. Suppose you have a new object called `Widget` that can transduce a string into some other string (with some optional continuous parameter). Thus, here we create a new file `widget.cc` like this

    #include "festival.h"
    #include "widget.h"  // definitions for the widget class

In order to register the widgets as Lisp objects we actually need to register them as `EST_Val`’s as well. Thus we now need

    VAL_REGISTER_CLASS(widget,Widget)
    SIOD_REGISTER_CLASS(widget,Widget)

The first names given to these functions should be a short mnenomic name for the object that will be used in the defining of a set of access and construction functions. It of course must be unique within the whole system. The second name is the name of the object itself.

To understand its usage we can add a few simple widget manipulation functions

    LISP widget_load(LISP filename)
    {
       EST_String fname = get_c_string(filename);
       Widget *w = new Widget;   // build a new widget

       if (w->load(fname) == 0)  // successful load
          return siod(w);
       else
       {
          cerr << "widget load: failed to load \"" << fname << "\"" << endl;
          festival_error();
       }
       return NIL;  // for compilers that get confused
    }

Note that the function `siod` constructs a LISP object from a `widget`, the class register macro defines that for you. Also note that when giving an object to a `LISP` object it then owns the object and is responsible for deleting it when garbage collection occurs on that `LISP` object. Care should be taken that you don’t put the same object within different `LISP` objects. The macros `VAL_RESGISTER_CLASS_NODEL` should be called if you do not want your given object to be deleted by the LISP system (this may cause leaks).

If you want refer to these functions in other files within your models you can use

    VAL_REGISTER_CLASS_DCLS(widget,Widget)
    SIOD_REGISTER_CLASS_DCLS(widget,Widget)

in a common `.h` file

The following defines a function that takes a LISP object containing a widget, applies some method and returns a string.

    LISP widget_apply(LISP lwidget, LISP string, LISP param)
    {
        Widget *w = widget(lwidget);
        EST_String s = get_c_string(string);
        float p = get_c_float(param);
        EST_String answer;

        answer = w->apply(s,p);

        return strintern(answer);
    }

The function `widget`, defined by the registration macros, takes a `LISP` object and returns a pointer to the `widget` inside it. If the `LISP` object does not contain a `widget` an error will be thrown.

Finally you wish to add these functions to the Lisp system

    void festival_widget_init()
    {
      init_subr_1("widget.load",widget_load,
        "(widget.load FILENAME)\n\
      Load in widget from FILENAME.");
      init_subr_3("widget.apply",widget_apply,
        "(widget.apply WIDGET INPUT VAL)\n\
      Returns widget applied to string iNPUT with float VAL.");
    }

In your `Makefile` for this directory you’ll need to add the include directory where `widget.h` is, if it is not contained within the directory itself. This is done through the make variable `LOCAL_INCLUDES` as

    LOCAL_INCLUDES = -I/usr/local/widget/include

And for the linker you’ll need to identify where your widget library is. In your `festival/config/config` file at the end add

    COMPILERLIBS += -L/usr/local/widget/lib -lwidget