wfst_regex.cc

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/*                Centre for Speech Technology Research                  */
/*                     University of Edinburgh, UK                       */
/*                         Copyright (c) 1997                            */
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/*************************************************************************/
/*                     Author :  Alan W Black                            */
/*                     Date   :  November 1997                           */
/*-----------------------------------------------------------------------*/
/*                                                                       */
/* WFST functions for building from REGEXs                               */
/*                                                                       */
/*=======================================================================*/
#include <iostream>
#include "EST_cutils.h"
#include "EST_WFST.h"

using namespace std;

void EST_WFST::build_or_transition(int start, int end, LISP disjunctions)
{
    // Choice of either disjunct
    LISP l;
    int intermed;

    if (disjunctions == NIL)
    cerr << "WFST construct: disjunct is nil\n";

    for (l=disjunctions; l != NIL; l=cdr(l))
    {
    // Can't go directly to end as other transitions could be added there
    intermed = add_state(wfst_nonfinal);
    build_wfst(start,intermed,car(l));
    build_wfst(intermed,end,epsilon_label());
    }
}

void EST_WFST::build_and_transition(int start, int end, LISP conjunctions)
{
    // require each conjunct in turn
    int intermed,lstart;
    LISP l;

    if (conjunctions == NIL)
    cerr << "WFST build: conjunct is nil\n";

    lstart = start;
    for (l=conjunctions; cdr(l) != NIL; l=cdr(l))
    {
    intermed = add_state(wfst_nonfinal);
    build_wfst(lstart,intermed,car(l));
    lstart = intermed;
    }
    build_wfst(lstart,end,car(l));
    
}

int EST_WFST::terminal(LISP l)
{
    // true, l is a terminal in a regex

    if (atomp(l))
    return TRUE;
    else
    return FALSE;
}

int EST_WFST::operator_or(LISP l)
{
    if (l && !consp(l) && (streq("or",get_c_string(l))))
    return TRUE;
    else
    return FALSE;
}

int EST_WFST::operator_plus(LISP l)
{
    if (l && !consp(l) && (streq("+",get_c_string(l))))
    return TRUE;
    else
    return FALSE;
}

int EST_WFST::operator_not(LISP l)
{
    if (l && !consp(l) && (streq("not",get_c_string(l))))
    return TRUE;
    else
    return FALSE;
}

int EST_WFST::operator_star(LISP l)
{
    if (l && !consp(l) && (streq("*",get_c_string(l))))
    return TRUE;
    else
    return FALSE;
}

int EST_WFST::operator_optional(LISP l)
{
    if (l && !consp(l) && (streq("?",get_c_string(l))))
    return TRUE;
    else
    return FALSE;
}

int EST_WFST::operator_and(LISP l)
{
    if (l && !consp(l) && (streq("and",get_c_string(l))))
    return TRUE;
    else
    return FALSE;
}

void EST_WFST::build_wfst(int start, int end,LISP regex)
{
    if (terminal(regex))
    {
    // unpack the label
    int in,out;
    EST_String s_name(get_c_string(regex));
    if (s_name.contains("/"))
    {
        in = p_in_symbols.name(s_name.before("/"));
        out = p_out_symbols.name(s_name.after("/"));
    }
    else
    {
        in = p_in_symbols.name(get_c_string(regex));
        out = p_out_symbols.name(get_c_string(regex));
    }
    if ((in == -1) || (out == -1))
        cerr << "WFST_build: symbol " <<  get_c_string(regex) <<
               " not in alphabet\n";
    p_states[start]->add_transition(0,end,in,out);
    }
    else if (operator_or(car(regex)))
    build_or_transition(start,end,cdr(regex));
    else if (operator_plus(car(regex)))
    {
    build_wfst(start,end,cdr(regex));
    build_wfst(end,end,cdr(regex));
    }
    else if (operator_star(car(regex)))
    {
    build_wfst(start,start,cdr(regex));
    build_wfst(start,end,epsilon_label());
    }
    else if (operator_not(car(regex)))
    {
    int errstate = add_state(wfst_error);
    build_and_transition(start,errstate,cdr(regex));
    }
    else if (operator_optional(car(regex)))
    {
    build_wfst(start,end,cdr(regex));
    build_wfst(start,end,epsilon_label());
    }
    else if (operator_and(car(regex))) 
    build_and_transition(start,end,cdr(regex));
    else
    build_and_transition(start,end,regex);  // default is and
}

void EST_WFST::build_from_regex(LISP inalpha, LISP outalpha, LISP regex)
{

    clear();

    cout << "building from regex: " << endl;
    pprint(regex);

    init(inalpha,outalpha);   // alphabets
    if (regex == NIL)
    p_start_state = add_state(wfst_final);  // empty WFST
    else 
    {
    p_start_state = add_state(wfst_nonfinal);
    int end = add_state(wfst_final);
    build_wfst(p_start_state,end,regex);
    }
}