

_I_s _a _V_a_r_i_a_b_l_e _D_e_f_i_n_e_d?

     exists(x, where =NULL, envir=sys.frame(sys.parent()), frame =NULL,
            mode = "any", inherits = TRUE)

_A_r_g_u_m_e_n_t_s:

       x: a variable name (given as a quoted string).

where, envir, frame: an environent to be searched. By
          default this is the environment where the call to
          `envir' takes place.

    mode: the type of interest for the object.

inherits: should the enclosing frames of the environment be
          inspected.

_D_e_s_c_r_i_p_t_i_o_n:

     This function looks to see if the name `x' has a value
     bound to it.  If `inherits' is `TRUE' and a value is
     not found for `x', then the parent frames of `envir'
     are searched until the name `x' is encountered.  If
     `mode' is specified then only objects of that mode are
     sought.  The function returns `TRUE' if the variable is
     encountered and `FALSE' if not.

_S_e_e _A_l_s_o:

     `get'.

_E_x_a_m_p_l_e_s:

     ##  Define a substitute function if necessary:
     if(!exists("some.fun", mode="function"))
      some.fun <- function(x) { cat("some.fun(x)\n"); x }

