/* 1 3 val=feval(\\"type\\",cr,x), evaluate parameterized function
*/

// Data defined for all feval callbacks
//
#define FEVAL_START i[0]	// initialized to 1, set to 0 on first callback call
#define FEVAL_X d[0]		// input x value
#define FEVAL_R d[1]		// result value, initialized to 0

static void rf_feval_poly_callback( Data *d)
{
  if( d->FEVAL_START)
  {
    d->FEVAL_START = 0;
    d->FEVAL_R = eval_cell( d->cp, &d->c);
  }
  else // using Horner's rule
  {
    d->FEVAL_R = eval_cell( d->cp, &d->c) + d->FEVAL_X*d->FEVAL_R;
  }
}

static struct feval_callback
{
  const char *type; Traverse_Callback tc; int direction;
}
feval_callbacks[] =
{
  { "poly",	rf_feval_poly_callback,	-1 },
//***
// add other function types and callbacks here...
//***
  {      0,	0,			0 },
};

double rf_feval(const Node *n, const Cell *c)
{
  Data d;
  struct feval_callback *cb;
  Traverse_Callback tc = NULL;

  Node *type = Right(n);
  Node *cr = type->next;
  Node *x = cr->next;

  if( type->type != STRING)
  {
    fprintf( out, "feval: first argument must be a string\n");
    return 0;
  }

  for( cb = feval_callbacks; cb->type; ++cb)
    if( strcmp( cb->type, type->u.str) == 0) { tc = cb->tc; break; }

  if( tc == NULL)
  {
    fprintf( out, "feval: unknown function type \"%s\"\n", type->u.str);
    return 0;
  }

  if( check_range( cr, "feval: second argument")) return 0;

  if( x->type == RANGE)
  {
    fprintf( out, "feval: third argument can not be a range\n");
    return 0;
  }

  d.FEVAL_START = 1;
  d.FEVAL_X = eval_tree( x, c);
  d.FEVAL_R = 0;

  ss_traverse_range_adjust( cr, c, tc, &d, cb->direction);

  return d.FEVAL_R;
}