Error types

The following types of errors can be detected:

		  arith_expr_expected

		  atom_expected 

		  char_code_expected

		  code_area_overflow

		  control_stack_overflow

		  could_not_open_stream

		  divide_by_zero

		  file_does_not_exist

		  float_format_expected

		  illegal_arguments 

		  illegal_expression

		  illegal_file

		  illegal_list

		  illegal_mode_string

		  illegal_predicate

		  integer_expected 

		  list_expected

		  nonvariable_expected

		  not_modifiable

		  number_expected

		  operator_type_expected

		  out_of_range

		  permission_error

		  structure_expected

		  undefined_predicate

		  variable_expected