There are several issues to consider here. The most important issue is how to get jed to display 8 bit characters in a “clean” way. By “clean” I mean any character with the high bit set is sent to the display device as is. This is achieved by putting the line:
DISPLAY_EIGHT_BIT = 1;
in the jed.rc (.jedrc) startup file. European systems might
want to put this in the file site.sl for all users. The default is
1 so unless its value has been changed, this step may not be necessary.
There is another issue. Suppose you want to display 8 bit characters with
extended Ascii codes greater than or equal to some value, say 160. This
is done by putting DISPLAY_EIGHT_BIT = 160;. I believe that ISO
Latin character sets assume this. This is the default value for Unix and
VMS systems.
Inputting characters with the high bit set into jed is another issue.
How jed interprets this bit is controlled by the variable
META_CHAR. What happens is this: When jed reads a character from
the input device with the high bit set, it:
META_CHAR. If this value is -1, jed simply
inserts the character into the buffer.META_CHAR in the range 0 to 255, jed
returns two 7-bit characters. The first character returned is
META_CHAR itself. The next character returned is the original
character but with the high bit stripped.
The default value of META_CHAR is -1 which means that when jed sees
a character with the high bit set, jed leaves it as is. Please note that
a character with the high bit set it cannot be the prefix character
of a keymap. It can be a part of the keymap but not the prefix.
Some systems only handle 7-bit character sequences and as a result, jed
will only see 7-bit characters. jed is still able to insert any
character in the range 0-255 on a 7-bit system. This is done through the
use of the quoted_insert function which, by default, is bound to
the backquote key ‘. If the quoted_insert function is called
with a digit argument (repeat argument), the character with the value of
the argument is inserted into the buffer. Operationally, one hits
Esc, enters the extended Ascii code and hits the backquote key. For
example, to insert character 255 into the buffer, simply press the
following five keys: Esc 2 5 5 ‘.
The above discussion centers around input and output of characters with the high bit set. How jed treats them internally is another issue and new questions arise. For example, what is the uppercase equivalent of a character with ASCII code 231? This may vary from language to language. Some languages even have characters whose uppercase equivalent correspond to multiple characters. For jed, the following assumptions have been made:
It would be nice if a fourth assumption could be made:
However, apparently this is not possible since most IBMPC character sets violate this assumption. Hence, jed does not assume it. Suppose X is the upper case value of some character and suppose Y is its lower case value. Then to make jed aware of this fact and use it case conversions, it may be necessary to put a statement of the form:
define_case (X, Y);
in the startup file. For example, suppose 211 is the uppercase of 244. Then, the line
define_case (211, 244);
will make jed use this fact in operations involving the case of a character.
This has already been done for the ISO Latin 1 character set. See the file
iso-latin.sl for details. For MSDOS, this will not work. Instead
use the files dos437.sl and dos850.sl. By default, jed’s
internal lookup tables are initialized to the ISO Latin set for Unix and
VMS systems and to the DOS 437 code page for the IBMPC. To change the
defaults, it is only necessary to load the appropriate file. For example,
to load dos850.sl definitions, put
evalfile ("dos850"); pop ();
in the startup file (e.g., site.sl). In addition to
uppercase/lowercase information, these files also contain word
definitions, i.e., which characters constitute a “word”.