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NMODE for EMODE users
Alan Snyder
28 October 1982
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NMODE is a new PSL text editor installed at HP.

This note describes the NMODE editor in terms of its differences from EMODE,
the previous PSL text editor.  NMODE is a new editor that retains much of the
basic structure and algorithms of EMODE.  However, there are many differences
between NMODE and EMODE, of interest to both users and experts.

For experts, the differences can be summed up very easily: NMODE is a complete
rewrite of EMODE.  Virtually no EMODE function or fluid variable is present in
NMODE.  Thus, any code that interacts with the insides of EMODE must be
rewritten to run in NMODE.  Even code to define new function keys must be
changed.  In many cases, it is only necessary to change function names.
However, code that accesses EMODE fluid variables probably requires greater
revision, since many EMODE fluid variables have no counterparts in NMODE.  In
particular, there are no fluid variables containing information about the
current buffer or the current window.  Information describing how to customize
NMODE by redefining keys or defining new commands may be found in the file
"PSL:NMODE-CUSTOMIZING.TXT".

For users, the differences between NMODE and EMODE can be divided into a number
of categories:

  * New Lisp Interaction
  * Incompatible Changes
  * Limitations
  * Extension of existing commands to conform to EMACS
  * New EMACS commands implemented
  * Bug Fixes
  * Miscellaneous Improvements

These categories are described below:

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* New Lisp Interaction

NMODE provides a new set of editor commands for executing forms from a buffer
and interacting with the Break Handler.  These commands use a new prefix
character, C-], which echoes as "Lisp-".  In the remainder of this document,
the notation "Lisp-X" will be used to refer to the command sequence C-] X
(where X is an arbitrary character).  The "Lisp-" commands are available only
in Lisp Mode.

Three "Lisp-" commands are always available in Lisp mode:

  Lisp-E executes a form in the current buffer beginning at the start of the
current line.  (This command was invoked as M-E in EMODE.)  Output produced by
the execution of a Lisp form is written to an output buffer (called "OUTPUT" in
NMODE), which will pop up automatically in the "other" window if it is not
exposed when output occurs.  As in EMODE, this automatic pop-up can be
suppressed by setting the global variable *OutWindow to NIL; however, in NMODE,
this flag will be ignored when a Break occurs.  In NMODE, output is always
written at the END of the output buffer, even if the input is coming from the
same buffer.  Thus, when you execute a form from the output buffer, the cursor
will jump to the end of the buffer when the output is printed.  However, the
mark is set at the point where you did the Lisp-E, so you can get back using
C-X C-X.

  Lisp-Y will yank the output from the previous Lisp-E into the current buffer.
(This command was invoked as C-M-Y in EMODE.)  The output is obtained from the
output buffer.  Only the starting and ending positions of the last output text
are saved, so that if the output buffer has been modified, Lisp-Y may get the
wrong text.

  Lisp-L will transfer to a "normal" PSL Lisp Listener.  (This command was
invoked as C-M-Z in EMODE.)  To return to NMODE, evaluate the form (NMODE).

In NMODE, the Lisp prompt is displayed as part of the window label when the
OUTPUT buffer is displayed, as opposed to permanently reserving a separate line
on the screen for the Lisp prompt as EMODE does.

NMODE does not use a break menu.  However, NMODE does provide a set of special
commands that can be used when a Lisp evaluation has entered a break loop.
These commands are:

	Lisp-B: print a backtrace
	Lisp-Q: quit out of current break loop
	Lisp-A: abort to top-level (restarts NMODE)
	Lisp-R: retry (from a continuable error)
		(existing ErrorForm is re-evaluated)
	Lisp-C: continue (from a continuable error)
		(value of the last form executed is used for the value)
	Lisp-?: Brief help on above commands.

Lisp-C is used to return a new value as the result value of the offending form
(in the case of a continuable error).  The value is specified by executing a
form using Lisp-E; Lisp-C then "returns" the most recent result of execution.

Lisp-B by itself prints the normal backtrace.  C-U Lisp-B will in addition
print the names of "interpreter" functions, such as COND and PROG.  C-U C-U
Lisp-B will print a verbose backtrace that displays the entire contents of the
stack.

The PSL function YesP has been redefined in NMODE to use NMODE prompted string
input.  It requires that the user type "Yes" or "No".

-------------------------------------------------------------------------------
* Incompatible Changes

A number of existing EMODE functions are performed using different commands
in NMODE, leaving their original commands either undefined or doing something
different.  These are:

C-X C-R (Visit File): now C-X C-V (to conform with EMACS)
M-E (Execute Form): now Lisp-E (typed as: C-] E)
C-M-Y (Yank Last Output): now Lisp-Y (typed as: C-] Y)
C-M-Z (Exit NMode): now Lisp-L (typed as: C-] L)
C-X 2 (View Two Windows): now C-X 3 (to conform with EMACS)
C-M-O (Forward Up List): now C-M-) (same as EMACS)

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* Limitations

There are limitations imposed by NMODE that are not present in EMODE:

* Currently, NMODE can be used only with HP terminals and with the 9836
  running an extended VT52 emulator (the extensions are to support display
  enhancements).

* Currently, NMODE runs only on TOPS-20.

-------------------------------------------------------------------------------
* Extension of existing commands to conform to EMACS

A large number of existing EMODE commands have been extended in NMODE to
conform either exactly or more closely to the EMACS definitions.  Many of these
changes relate to the use of command arguments (specified by C-U).  In EMODE,
C-U simply defines a positive repetition count and repetitively executes the
definition of the following command character.  In NMODE, C-U works as in
EMACS: it can accept either a positive or negative argument, which is
interpreted in arbitrary ways by the following command.

The following EMODE commands have been extended in notable ways:

C-@		With an argument, pops a ring of marks (which is per-buffer).
C-K		Is unaffected by trailing white space at the end of the line.
C-L		Now repositions the current window.  Accepts C-U argument.
C-N and C-P	Now remember the "goal column".
C-V and M-V	Scroll by lines or screenfuls, according to C-U argument.
C-X 1		With an argument, expands the bottom window instead of the top.
C-X 2		Now makes the bottom window current (use C-X 3 for top window).
C-X C-S		Now won't save an unmodified buffer.
C-X C-V		Now offers to save a modified buffer.
C-X D		Obeys command argument (without arg, uses current directory).
C-X K		Now asks for the name of the buffer to kill.
C-X O		Now works even in 1-window mode.
M-< and M->	Now set the mark.
Return		Now will move "into" a region of blank lines.

-------------------------------------------------------------------------------
* New EMACS commands implemented

The following EMACS commands are newly implemented in NMODE:

BackSpace	Move Backward Character
C-%		Replace String
C-<		Mark Beginning
C->		Mark End
C-G		Aborts commands that request string input
C-M-(		Backward Up List
C-M-)		Forward Up List
C-M-O		Split Line
C-M-R		Reposition Window (for Lisp DEFUNs only)
C-M-Return	Same as M-M
C-M-T		Transpose Forms
C-M-Tab		Lisp Tab (also C-M-I)
C-M-V		Scroll other window
C-M-W		Append Next Kill
C-Rubout	Delete Backward Hacking Tabs
C-Space		Same as C-@
C-X 3		View Two Windows
C-X 4		Visit in Other Window (Find File or Select Buffer)
C-X A		Append to Buffer
C-X C-N		Set Goal Column
C-X C-T		Transpose Lines
C-X G		Get Register
C-X T		Transpose Regions
C-X X		Put Register
C-^		The "control prefix" (used to type things like C-%)
M-0 thru M-9	Define a numeric argument (also C-0, C-M-0, etc.)
M-Hyphen	Defines a numeric argument (also C-Hyphen, C-M-Hyphen, etc.)
M-R		Move to Screen Edge
M-Return	Same as M-M
M-T		Transpose Words
M-Tab		inserts a "Tab" (also M-I)
M-~		Buffer Not Modified

-------------------------------------------------------------------------------
* Bug Fixes

In the process of writing NMODE, a number of bugs in EMODE were fixed.
These include:

* M-Y has been made "safe".  It checks that the contents of the region equal
  the contents of the current kill buffer before killing the region.
* Dired SORT commands no longer throw away all user-specified changes.
* The interaction between NMODE and the Lisp Environment is much more
  robust.  It is much more difficult to get NMODE "screwed up".
  In NMODE, it is possible to Quit out of an "Unexpected EOF" error.
* NMODE does not allow the user to select one of its internal buffers.
* In NMODE, string input can be terminated only by Return or C-G (C-G
  aborts the command).
* The M-? command now accepts any syntactically valid command, including
  character sequences using prefix characters.
* NMODE will not screw up if the cursor is moved into a part of a line that
  does not show on the display.
* The window position indicator ("--68%--") now works reasonably.
* EMODE always advances to the next line after a M-E; NMODE suppresses
  this action in two cases where it is spurious: (1) when NMODE is starting
  up, (2) when the buffer pointer is at the beginning of the line, such as
  after "executing" a number.

-------------------------------------------------------------------------------
  * Miscellaneous Improvements

* NMODE supports INIT files.  When first started up, NMODE will execute
  the file "NMODE.INIT" on the user's home directory, if the file exists.
  The file should contain a sequence of Lisp forms.
* Completion of buffer names is implemented in NMODE.  Completion is
  requested using the Space character.
* File names now always expand to the full "true" file name (as in EMACS).
  As a result, Find File will always find a file in an existing buffer if
  possible, regardless of the exact string typed by the user.  In addition,
  file names specified by the user now MERGE with the default file name.
* Find File now creates a reasonable buffer name, instead of using the
  exact string typed by the user.  The buffer name will not be displayed
  on the mode line, if it is completely redundant.
* "Lisp" and "Text" modes are now available; the choice is based on file name.
  In "Text" mode, the Lisp related commands (both C-M-* and Lisp-*) are
  undefined, Tab is self-inserting, and Rubout does not "hack tabs".
* The M-X extended command interface has been implemented.  The following
  M-X commands are defined: "M-X Lisp Mode" and "M-X Text Mode", which
  set the mode of the current buffer.
* Display Refresh is interruptible, allowing faster type-ahead.  Parenthesis
  matching is also interruptible, which is especially important in the case
  of inserting an unmatched parenthesis.
* Prompting has been improved.
* Horizontal scrolling is supported.  Two new commands, C-X < and C-X >,
  are provided to scroll the window horizontally.  They accept a C-U argument.
* The buffer display now shows a '!' at the end of any line that extends
  past the right edge of the screen.
* Displaying one buffer in two windows now works reasonably.
* Each buffer has a modified flag which indicates whether the contents of
  the buffer have been changed since the buffer was last read or written.
* The "mode line" now uses inverse video and is much more like EMACS.
* Display enhancements are supported in a general fashion.  A new command
  C-X V has been implemented to switch between normal and inverse video.
* When entering string input, C-R will yank the default string into the input
  buffer.

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