:-  :~  navhome/'/docs/'
        next/'true'
        sort/'6'
        title/'C'
    ==
;>

# C

The actual production interpreter.  Note gotos for tail-call elimination,
and manual reference counting.  More about the C environment can be found 
in the [runtime system documentation](../../../runtime).

```
/* nock(): produce .*(bus fol).  Do not virtualize.
*/
static u3_noun
nock(u3_noun bus, u3_noun fol)
{
  u3_noun hib, gal;

  while ( 1 ) {
    hib = u3h(fol);
    gal = u3t(fol);

    if ( c3y == u3r_du(hib) ) {
      u3_noun poz, riv;

      poz = nock(u3k(bus), u3k(hib));
      riv = nock(bus, u3k(gal));

      u3a_lose(fol);
      return u3i_cell(poz, riv);
    }
    else switch ( hib ) {
      default: return u3m_bail(c3__exit);

      case 0: {
        if ( c3n == u3r_ud(gal) ) {
          return u3m_bail(c3__exit);
        }
        else {
          u3_noun pro = u3k(u3at(gal, bus));

          u3a_lose(bus); u3a_lose(fol);
          return pro;
        }
      }
      c3_assert(!"not reached");

      case 1: {
        u3_noun pro = u3k(gal);

        u3a_lose(bus); u3a_lose(fol);
        return pro;
      }
      c3_assert(!"not reached");

      case 2: {
        u3_noun nex = nock(u3k(bus), u3k(u3t(gal)));
        u3_noun seb = nock(bus, u3k(u3h(gal)));

        u3a_lose(fol);
        bus = seb;
        fol = nex;
        continue;
      }
      c3_assert(!"not reached");

      case 3: {
        u3_noun gof, pro;

        gof = nock(bus, u3k(gal));
        pro = u3r_du(gof);

        u3a_lose(gof); u3a_lose(fol);
        return pro;
      }
      c3_assert(!"not reached");

      case 4: {
        u3_noun gof, pro;

        gof = nock(bus, u3k(gal));
        pro = u3i_vint(gof);

        u3a_lose(fol);
        return pro;
      }
      c3_assert(!"not reached");

      case 5: {
        u3_noun wim = nock(bus, u3k(gal));
        u3_noun pro = u3r_sing(u3h(wim), u3t(wim));

        u3a_lose(wim); u3a_lose(fol);
        return pro;
      }
      c3_assert(!"not reached");

      case 6: {
        u3_noun b_gal, c_gal, d_gal;

        u3x_trel(gal, &b_gal, &c_gal, &d_gal);
        {
          u3_noun tys = nock(u3k(bus), u3k(b_gal));
          u3_noun nex;

          if ( 0 == tys ) {
            nex = u3k(c_gal);
          } else if ( 1 == tys ) {
            nex = u3k(d_gal);
          } else return u3m_bail(c3__exit);

          u3a_lose(fol);
          fol = nex;
          continue;
        }
      }
      c3_assert(!"not reached");

      case 7: {
        u3_noun b_gal, c_gal;

        u3x_cell(gal, &b_gal, &c_gal);
        {
          u3_noun bod = nock(bus, u3k(b_gal));
          u3_noun nex = u3k(c_gal);

          u3a_lose(fol);
          bus = bod;
          fol = nex;
          continue;
        }
      }
      c3_assert(!"not reached");

      case 8: {
        u3_noun b_gal, c_gal;

        u3x_cell(gal, &b_gal, &c_gal);
        {
          u3_noun heb = nock(u3k(bus), u3k(b_gal));
          u3_noun bod = u3nc(heb, bus);
          u3_noun nex = u3k(c_gal);

          u3a_lose(fol);
          bus = bod;
          fol = nex;
          continue;
        }
      }
      c3_assert(!"not reached");

      case 9: {
        u3_noun b_gal, c_gal;

        u3x_cell(gal, &b_gal, &c_gal);
        {
          u3_noun seb = nock(bus, u3k(c_gal));
         
          if ( c3n == u3r_ud(b_gal) ) {
            return u3m_bail(c3__exit);
          }
          else {
            u3_noun nex = u3k(u3at(b_gal, seb));

            u3a_lose(fol);
            bus = seb;
            fol = nex;
            continue;
          }
        }
      }
      c3_assert(!"not reached");

      case 10: {
        u3_noun p_gal, q_gal;

        u3x_cell(gal, &p_gal, &q_gal);
        {
          u3_noun zep, hod, nex;

          if ( c3y == u3r_du(p_gal) ) {
            u3_noun b_gal = u3h(p_gal);
            u3_noun c_gal = u3t(p_gal);
            u3_noun d_gal = q_gal;

            zep = u3k(b_gal);
            hod = nock(u3k(bus), u3k(c_gal));
            nex = u3k(d_gal);
          }
          else {
            u3_noun b_gal = p_gal;
            u3_noun c_gal = q_gal;

            zep = u3k(b_gal);
            hod = u3_nul;
            nex = u3k(c_gal);
          }

          u3a_lose(zep);
          u3a_lose(hod);

          return nock(bus, nex);
        }
      }
      c3_assert(!"not reached");
    }
  }
}
```