NAME
        function_exists - find out if a named function is defined in an
        object and return the object filename.

SYNOPSIS
         string function_exists(string func, object ob)

DESCRIPTION
        This function searches for a named function `func' in the specified
        object `ob'. If it is found, the filename of that object is returned.

        The filename returned is not the same as the string returned by
        the function `file_name()', it does not have the instance number
        of the found object suffixed to it.

        If no argument `ob' is given, `this_object()' is used by default.

NOTA BENE
        It is the filename of the object that contains the function that
        is returned, not the composite object that might inherit the file
        that contains the function.

        E.g: if the function is in an object inherited by `ob' the filename
        of the inherited object.

BUGS
        Does not find the function "heart_beat".

SEE ALSO
        inherit_list