# This function returns the "shape" (that is, the dimensions) of the
# entity `x'.  If `x' is a scalar, it returns NULL.  If `x' is a
# vector, it returns a scalar having the length of `x' as its value.
# If `x' is a matrix, it returns a vector having the number of rows
# and the number of columns as its first and second elements,
# respectively.  If `x' has any other class, an exception is raised.

shape = function (x)
{
  return self.(class(x)) (x);
};

( shape.table =
  shape.("function") =
  shape.("NULL") = strip (
    function (x)
    {
      message ("run time error:  Invalid %s argument for shape."; class (x));
      exception ();
    })
);

shape.scalar = function (x) { return NULL; };
shape.vector = function (x) { return x.ne; };
shape.matrix = function (x) { return x.nr, x.nc; };