/* j/6/ut_burn.c
**
*/
#include "all.h"


/* logic
*/
  static u3_noun
  _burn_in(u3_noun van, u3_noun sut, u3_noun gil);

  static u3_noun
  _burn_fork(u3_noun van,
             u3_noun yed,
             u3_noun gil)
  {
    if ( u3_nul == yed ) {
      return u3_nul;
    } else {
      u3_noun dis = _burn_in(van, u3h(yed), gil);
      u3_noun mor = _burn_fork(van, u3t(yed), gil);

      if ( u3_nul == dis ) return mor;
      if ( u3_nul == mor ) return dis;
      {
        u3_noun u_dis = u3t(dis);
        u3_noun u_mor = u3t(mor);

        if ( u3du(u_dis) == u3du(u_mor) ) {
          if ( c3y == u3qc_gor(u_mor, u_dis) ) {
            u3z(dis);
            return mor;
          } else {
            u3z(mor);
            return dis;
          }
        } else {
          if ( c3y == u3ud(u_dis) ) {
            u3z(mor);
            return dis;
          }
          else {
            u3z(dis);
            return mor;
          }
        }
      }
    }
  }

  static u3_noun
  _burn_in(u3_noun van,
           u3_noun sut,
           u3_noun gil)
  {
    u3_noun p_sut, q_sut, pq_sut, qq_sut, rq_sut, prq_sut, qrq_sut;

    if ( c3n == u3du(sut) ) switch ( sut ) {
      default: return u3m_bail(c3__fail);

      case c3__noun: return u3nc(u3_nul, 0);
      case c3__void: {
        return u3_nul;
      }
    }
    else switch ( u3h(sut) ) {
      default: return u3m_bail(c3__fail);

      case c3__atom: u3x_cell(u3t(sut), &p_sut, &q_sut);
      {
        if ( c3y == u3du(q_sut) ) {
          return u3nc(u3_nul, u3k(u3t(q_sut)));
        } else {
          return u3nc(u3_nul, 0);
        }
      }
      case c3__cell: u3x_cell(u3t(sut), &p_sut, &q_sut);
      {
        u3_noun hed = _burn_in(van, p_sut, gil);

        if ( u3_nul == hed ) {
          return u3_nul;
        }
        else {
          u3_noun tal = _burn_in(van, q_sut, gil);

          if ( u3_nul == tal ) {
            u3z(hed);
            return u3_nul;
          }
          else {
            u3_noun ret = u3nt(u3_nul, u3k(u3t(hed)), u3k(u3t(tal)));

            u3z(hed);
            u3z(tal);
            return ret;
          }
        }
      }
      case c3__core: u3x_cell(u3t(sut), &p_sut, &q_sut);
                     u3x_trel(q_sut, &pq_sut, &qq_sut, &rq_sut);
                     u3x_cell(rq_sut, &prq_sut, &qrq_sut);
      {
        u3_noun pay = _burn_in(van, p_sut, gil);

        if ( u3_nul == pay ) {
          return u3_nul;
        }
        else {
          u3_noun ret = u3nt(u3_nul, u3k(prq_sut), u3k(u3t(pay)));

          u3z(pay);
          return ret;
        }
      }
      case c3__fuss:
      case c3__face: u3x_cell(u3t(sut), &p_sut, &q_sut);
      {
        return _burn_in(van, q_sut, gil);
      }
      case c3__fork: p_sut = u3t(sut);
      {
        u3_noun yed = u3qdi_tap(p_sut, u3_nul);
        u3_noun ret = _burn_fork(van, yed, gil);

        u3z(yed);
        return ret;
      }
      case c3__hold:
      {
        if ( (c3y == u3qdi_has(gil, sut)) ) {
          return u3_nul;
        }
        else {
          u3_noun zoc = u3qdi_put(gil, sut);
          u3_noun fop = u3qfu_repo(van, sut);
          u3_noun pro = _burn_in(van, fop, zoc);

          u3z(fop);
          u3z(zoc);

          return pro;
        }
      }
    }
  }

  u3_noun
  _cqfu_burn(u3_noun van,
             u3_noun sut)
  {
    u3_noun unt = _burn_in(van, sut, u3_nul);

    if ( u3_nul == unt ) {
      return u3m_error("burn");
    } 
    else {
      u3_noun ret = u3k(u3t(unt));

      u3z(unt);
      return ret;
    }
  }

  u3_noun
  u3qfu_burn(u3_noun van,
             u3_noun sut)
  {
    c3_m    fun_m = c3__burn + !!u3r_at(u3qfu_van_vet, van);
    u3_noun pro   = u3z_find(fun_m, sut);

    if ( u3_none != pro ) {
      return pro;
    }
    else {
      pro = _cqfu_burn(van, sut);

      return u3z_save(fun_m, sut, pro);
    }
  }

  u3_noun
  u3wfu_burn(u3_noun cor)
  {
    u3_noun sut;

    if ( u3_none == (sut = u3r_at(u3x_sam, cor)) ) {
      return u3m_bail(c3__fail);
    } else {
      return u3qfu_burn(cor, sut);
    }
  }