reduce-historical/psl-1983/doc/zpedit.doc

			THE UCI-LISP EDITOR
		    (Translated to Standard LISP)

SLISP provides an extremely powerful form-oriented editor.  This
facility allows the user to easily alter function definitions,
variable values and property list entries.  It thereby makes it
entirely unnecessary for the user to employ a conventional text
editor in the maintenance of programs.  This document is a guide
to using the editor.  Certain features of the UCI-LISP editor have
not been incorporated in the translated editor, and we have tried 
to mark all such differences.


	Section 1: User Entry to Editor

This section describes normal user entry to the editor (EDITF, 
EDITP and EDITV) and the editing commands which are available.
This section is by no means complete.  In particular, material
covering programmed calls to the editor routines is not treated.
Consult the UCI LISP manual for further details.

To edit a function named FOO do
*(EDITF FOO)

To edit the value of an atom named BAZ do
*(EDITV FOO)

To edit the property list of an atom named FOOBAZ do
*(EDITP FOO)
Warning, editing the property list of an atom may position pointers at
unprintable structures. It is best to use the F (find) command before
trying to print property lists.  This editor capability is variable from
implementation to implementatio. 

The Editor will prompt with 
-E-
*
You can then input any editor command.  The input scanner is not very smart.
It terminaes its scan and begins processing when it sees a printable character
immediately followed by a carriage return.  Do not use escape to terminate
an editor command.  If the editor seems to be repeatedly requesting input
type P<ret> (print the current expression) or some other command that will 
ordinarily do no damage, but will terminate the input soliciitation.


The following set of topics makes a good 'first glance' at the
editor.
	Entering the editor: EDITF, EDITV.
	Leaving the editor:  OK.
	Editor's attention:  CURRENT-EXP.
	Changing attention:  POS-INTEGER, NEG-INTEGER, 0, ^, NX, BK.
	Printing:	     P, PP.
	Modification:	     POS-INTEGER, NEG-INTEGER, A, B, :, N.
	Changing parens:     BI, BO.
	Undoing changes:     UNDO.

For the more discriminating user, the next topics might be some
of the following.
	Searches:	     PATTERN, F, BF.
	Complex commands:    R, SW, XTR, MBD, MOVE.
	Changing parens:     LI, LO, RI, RO.
	Undoing changes:     TEST, UNBLOCK, !UNDO.

Other features should be skimmed but not studied until it appears
that they may be useful.
	

SECTION 2:  Editor Command Reference

(A exp1 exp2 ... expn)					edit cmnd
This command inserts exp1 thru expn (arbitrary LISP expressions)
after the current expression.  This is accomplished by doing an UP 
and a (-2 exp1 exp2 ... expn) or an (N exp1 exp2 ... expn), as 
appropriate.  Note the way in which the current expression is 
changed by the UP.

(B exp1 exp2 ... expn)					edit cmnd
This command inserts exp1 thru expn (arbitrary LISP forms) before
the current expression.  This is accomplished by doing an UP
followed by a (-1 exp1 exp2 ... expn).  Note the way in which the
current expression is changed by the UP.

(BELOW com n)						edit cmnd
This command changes the current expression in the following manner.
The edit command com is executed.  If com is not a recognized 
command, then (_ com) is executed instead.  Note that com should
cause ascent in the edit chain (i.e., should be equivalent to
some number of zeroes).  BELOW then evaluates (note!) n and
descends n links in the resulting edit chain.  That is, BELOW
ascends the edit chain (does repeated 0s) looking for the link 
specified by com and stops n links below that (backs off n 0s).

If n is not given, 1 is assumed.

BF pat							edit cmnd
(BF pat flg)						edit cmnd
This command performs a backwards find, searching for pat (an
edit pattern).  Search begins with the expression immediately
before the current expression and proceeds in reverse print
order.  (If the current expression is the top level expression,
the entire expression is searched in reverse print order.)
Search begins at the end of each list, and descends into each
element before attempting to match that element.  If the match
fails, proceed to the previous element, etc. until the front
of the list is reached.  At that point, BF ascends and backs
up, etc.  

The search algorithm may be slightly modified by use of the second
form of the command.  Possible flgs and their meanings are as
follows.
	T - begins search with the current expression rather than
		with the preceeding expression at this level.
	NIL or missing - same as BF pat.

NOTE:  if the variable UPFINDFLG is non-NIL, the editor does
an UP after the expression matching pat is located.  Thus,
doing a BF for a function name yields a current expression
which is the entire function call.  If this is not desired,
UPFINDFLG may be set to NIL.  UPFINDFLG is initially T.

BF is protected from circular searches by the variable MAXLEVEL.
If the total number of CARs and CDRs descended into reaches
MAXLEVEL (initially 300), search of that tail or element is
abandoned exactly as though a complete search had failed.

(BI n1 n2)						edit cmnd
This command inserts a pair of parentheses in the current
expression.  (Note that parentheses are ALWAYS balanced, and
hence must be added or removed in pairs.)  A left paren is
inserted before element n1 of the current expression.  A right
paren is inserted after element n2 of the current expression.
Both n1 and n2 are usually integers, and element n2 must be to
the right of element n1.

(BI n1) is equivalent to (BI n1 n1).

The NTH command is used in the search, so that n1 and n2 may 
be any location specifications.  The expressions used will
be the first element of the current expression in which the
specified form is found at any level.

(BIND coms)						edit cmnd
This command provides the user with temporary variables for
use during the execution of the sequence of edit commands coms.
There are three variables available: #1, #2 and #3.  The binding
is recursive and BIND may be executed recursively if necessary.
All variables are initialized to NIL.  This feature is useful
chiefly in defining edit macros.

BK 							edit cmnd
The current expression becomes the expression immediately preceeding
the present current expression.  This command generates an error
if the current expression is the first expression in the list.

(BO n)							edit cmnd
The BO command removes a pair of parentheses from the nth element
of the current expression.  The parameter n is usually an integer.
The NTH command is used in the search, however, so that any 
location specification may be used.  The expression referenced is
the first element of the current expression in which the specified
form is found at any level.

(CHANGE loc TO exp1 exp2 ... expn)			edit cmnd
This command replaces the current expression after executing the
location specification loc by exp1 ... expn.

(COMS arg1 arg2 ... argn)				edit cmnd
This command evaluates its argi and executes them as edit commands.

(COMSQ com1 com2 ... comn)				edit cmnd
This command executes each comi as an edit command

At any given time, the attention of the editor is focused on a
single expression or form.  We call that form the current expression.
Editor commands may be divided into two broad classes.  Those
commands which change the current expression are called attention-
changing commands.  Those commands which modify structure are
called structure modification commands.

DELETE							edit cmnd
This command deletes the current expression.  If the current
expression is a tail, only the first element is deleted.  This
command is equivalent to (:).

E form							edit cmnd
(E form)						edit cmnd
(E form T)						edit cmnd
This command evaluates form.  The first form of the command is
valid only when typed in from the TTY.  (E form) evaluates form
and prints the value on the terminal.  The form (E form T)
evaluates form but does not print the result.

(EDITF fn coms)							fsubr
This function initiates editing of the function whose name is
fn.  The argument coms is an optional sequence of edit
commands.  If coms is present, no terminal input is requested
or required.  The commands in coms are executed and EDITF
returns fn.  If coms is not present, then the editor will
ask for keyboard input.

(EDITFNS fn-list coms)						fsubr
This function applies the sequence of editor commands, coms, to each
of several functions.  The argument fn-list is evaluated, and should
evaluate to a list of function names.  Coms will be applied to each
function in fn-list, in turn.  Errors in editing one function will
not affect editing of others.  The editor call is via EDITF, so that
values may also be edited in this way.  The value of the function 
is NIL.

(EDITP at coms)							fsubr
This function initiates editing of the property list of the 
atom whose name is at.  The argument coms is a possibly null
sequence of edit commands which will be executed before calling
for input from the terminal.

(EDITV at coms)							fsubr
This function initiates editing of the value of the atom whose
name is at.  The argument coms is a possibly null sequence of
edit commands which will be executed before calling for input
from the terminal.

(EMBED loc IN arg)					edit cmnd
This command replaces the expression which would be current after
executing the location specification loc by another expression
which has that expression as a sub-expression.  The manner in
which the transformation is carried out depends on the form of
arg.  If arg is a list, then each occurrence of the atom '*' in
arg is replaced by the expression which would be current after
doing loc.  (NOTE: a fresh copy is used for each substitution.)
If arg is atomic, the result is equivalent to:
	(EMBED loc IN (arg *)).
A call of the form (EMBED loc IN exp1 exp2 ... expn) is equivalent
to:
	(EMBED loc IN (exp1 exp2 ... expn *)).

If the expression after doing loc is a tail, EMBED behaves as
though the expression were the first element of that tail.

(EXTRACT loc1 FROM loc2)				edit cmnd
This command replaces the expression which would be current after
doing the location specification loc2 by the expression which
would be current after doing loc1.  The expression specified
by loc1 must be a sub-expression of that specified by loc2.

F pat							edit cmnd
(F pat flg)						edit cmnd
This command causes the next command, pat, to be interpreted
as a pattern.  The current expression is searched for the
next occurrence of pat.  If pat is a top level element of the
current expression, then pat matches that top level occurrence
and a full recursive search is not attempted.  Otherwise, the
search proceeds in print order.  Recursion is done first in
the CAR and then in the CDR direction.

The second form of the command, (F pat flg) may be used to
modify the search algorithm according to the value of flg.
Possible values and their actions are:
	N - suppresses the top-level check.  That is, finds
		the next print order occurrence of pat regardless
		of any top level occurrences.
	T - like N, but may succeed without changing the 
		current expression.  That is, succeeds even
		when the current expression itself is the
	   	only occurrence of pat.
	positive integer - finds the nth place at which pat is
		matched.  This is equivalent to (F pat T)
		followed by n-1 (F pat N)s.  If n occurrences
		are not found, the current expression is unchanged.
	NIL or missing - Only searches top level elements of the
		current expression.  May succeed without changing
		the current expression.

NOTE:  If the variable UPFINDFLG is non-NIL, F does an UP after
locating a match.  This ensures that F fn, where fn is a function
name, will result in a current expression which is the entire
function call.  If this is undesirable, set UPFINDFLG to NIL.
Its initial value is T.

As protection against searching circular lists, the search will
be abandoned if the total number of CAR-CDR descents exceeds
the value of the variable MAXLEVEL.  (The initial value is
300.)  The search fails just as if the entire element had
been unsuccessfully searched.

(FS pat1 pat2 ... patn)					edit cmnd
The FS command does sequential finds.  That is, it searches
(in print order) first for pat1, then for pat2, etc.  If any
search fails, the current expression is left at that form which
matched in the last successful search.  This command is,
therefore, equivalent to a sequence of F commands.

(F= exp flg)						edit cmnd
This command is equivalent to (F (== exp) flg).  That is, it
searches, in the manner specified by flg, for a form which is EQ
to exp.  Note that for keyboard typeins, this will always fail
unless exp is atomic.

HELP							edit cmnd
This command provides an easy way of invoking the HELP system
from the editor.

(I com arg1 arg2 ... argn)				edit cmnd
This command evaluates the argi and executes com on the resulting
values.  This command is thus equivalent to:
	(com val1 val2 ... valn),
where each vali is equal to (EVAL argi).

(IF arg)						edit cmnd
This command, useful in edit macros, conditionally causes an
editor error.  If (EVAL arg) is NIL (or if evaluation of arg
causes a LISP error), then IF generates an editor error.

(INSERT exp1 exp2 ... expn AFTER loc)			edit cmnd
(INSERT exp1 exp2 ... expn BEFORE loc)			edit cmnd
(INSERT exp1 exp2 ... expn FOR loc)			edit cmnd
The INSERT command provides equivalents of the A, B and : commands
incorporating a location specification, loc.  This command inserts
exp1 thru expn AFTER, BEFORE or FOR (in place of) the expression
which is current after executing loc.  Note, however, that the
current expression is not changed.

(LC loc)						edit cmnd
This command, which takes as an argument a location specification,
explicitly invokes the location specification search.  The current
expression is changed to that which is current after executing loc.

See LOC-SPEC for details on the definition of loc and the search
method in question.

(LCL loc)						edit cmnd
This command, which takes as an argument a location specification,
explicitly invokes the location specification search.  However,
the search is limited to the current expression itself.  The
current expression is changed to that which is current after
executing loc.

(LI n)							edit cmnd
This command inserts a left parenthesis (and, of course, a matching
right paren).  The left paren is inserted before the nth element
of the current expression and the right paren at the end of the
current expression.  Thus, this command is equivalent to
(BI n -1).

The NTH command is used in the search, so that n, which is usually
an integer, may be any location specification.  The expression
referenced is the first element of the current expression which
contains the form specified at any level.

(LO n)							edit cmnd
This command removes a left parenthesis (and a matching right
paren, of course) from the nth element of the current expression.
All elements after the nth are deleted.

The command uses the NTH command for the search.  The parameter n,
which is usually an integer, may be any location specification.
The expression actually referenced is the first element of the
current expression which contains the specified form at any depth.

Many of the more complex edit commands take as an argument a
location specification (abbreviated loc throughout this
document).  A location specification is a list of edit commands,
which are, with two exceptions, executed in the normal way.
Any command not recognized by the editor is treated as though
it were preceeded by F.  Furthermore, if one of the commands
causes an error and the current expression has been changed by
prior commands, the location operation continues rather than
aborting.  This is a sort of back-up operation.  For example,
suppose the location specification is (COND 2 3), and the
first clause of the first COND has only 2 forms.  The location
operation will proceed by searching for the next COND and
trying again.  If a point were reached in which there were
no more CONDs, the location operation would then fail.

(LP coms)						edit cmnd
This command, useful in macros, repeatedly executes coms (a sequence
of edit commands) until an editor error occurs.  When LP exits,
it prints the number of OCCURRENCES;  that is, the number of times
coms was successfully executed.  After execution of the command,
the current expression is left at what it was after the last complete
successful execution of coms.

The command terminates if the number of iterations exceeds the value
of the variable MAXLOOP (initially 30).

(LPQ coms)						edit cmnd
This command, useful in macros, repeatedly executes coms (a sequence
of edit commands) until an editor error occurs.  After execution
of the command, the current expression is left at what it was after
the last complete successful execution of coms.

The command terminates if the number of iterations exceeds the 
value of the variable MAXLOOP (initially 30).

This command is equivalent to LP, except that OCCURRENCES is not
printed.

(M nam coms)						edit cmnd
(M (nam) (arg1 arg2 ... argn) coms)			edit cmnd
(M (nam) arg coms)					edit cmnd
The editor provides the user with a macro facility.  The user
may define frequently used command sequences to be edit macros,
which may then be invoked simply by giving the macro name as
an edit command.  The M command provides the user with a
method of defining edit macros.

The first form of the command defines an atomic command which takes
no arguments.  The argument nam is the atomic name of the macro.
This defines nam to be an edit macro equivalent to the sequence
of edit commands coms.  If nam previously had definition as an
edit macro, the new definition replaces the old.  NOTE:  edit
command names take precedence over macros.  It is not possible
to redefine edit command names.

The second form of the M command defines a list command, which
takes a fixed number of arguments.  In this case, nam is defined 
to be an edit macro equivalent to the sequence of edit commands 
coms.  However, when (nam exp1 exp2 ... expn) is executed, the 
expi are substituted for the corresponding argi in coms before 
coms are executed.

The third form of the M command defines a list command which may
take an arbitrary number of arguments.  Execution of the macro
nam is accomplished by substituting (exp1 exp2 ... expn) (that
is, the CDR of the macro call (nam exp1 exp2 ... expn)) for
all occurrences of the atom arg in coms, and then executing
coms.

(MAKEFN (nam vars) args n1 n2)				edit cmnd
This command defines a portion of the current expression as a
function and replaces that portion of the expression by a call
to the function.  The form (nam vars) is the call which replaces
the n1st thru n2nd elements of the current expression.  Thus,
nam is the name of the function to be defined.  Vars is a sequence
of local variables (in the current expression), and args is a 
list of dummy variables.  The function definition is formed by
replacing each occurrence of an element in vars (the CDR of
(nam vars)) by the corresponding element of args.  Thus, args
are the names of the formal parameters in the newly defined 
function.

If n2 is omitted, it is assumed equal to n1.

MARK							edit cmnd
This command saves the current position within the form in such
a way that it can later be returned to.  The return is accomplished
via _ or __.

(MBD arg)						edit cmnd
This command replaces the current expression by some form which
has the current expression as a sub-expression.  If arg is a
list, MBD substitutes a fresh copy of the current expression for
each occurrence of the atom '*' in arg.  If arg is a sequence
of expressions, as:
		(MBD exp1 exp2 ... expn),
then the call is equivalent to one of the form:
		(MBD (exp1 exp2 ... expn *)).
The same is true if arg is atomic:
		(MBD atom) = (MBD (atom *)).

(MOVE loc1 TO com loc2)					edit cmnd
The MOVE command allows the user to move structure from one point
to another.  The user may specify the form to be moved (via loc1,
the first location specification), the position to which it is
to be moved (via loc2, the second location specification) and
the action to be performed there (via com).  The argument com
may be BEFORE, AFTER or the name of a list command (e.g., :,
N, etc.).  This command performs in the following manner.  Take
the current expression after executing loc1 (or its first element,
if it is a tail); call it expr.  Execute loc2 (beginning at the
current expression AS OF ENTRY TO MOVE -- NOT the expression which
would be current after execution of loc1), and then execute
(com expr).  Now go back and delete expr from its original 
position.  The current expression is not changed by this command.

If loc1 is NIL (that is, missing), the current expression is moved.
In this case, the current expression becomes the result of
the execution of (com expr).

If loc2 is NIL (that is missing) or HERE, then the current
expression specifies the point to which the form given by
loc2 is to be moved.

(N exp1 exp2 ... expn)					edit cmnd
This command adds exp1 thru expn to the end of the current
expression.  This compensates for the fact that the negative
integer command does not allow insertion after the last element.

-n							edit cmnd
(-n exp1 exp2 ... expn)				edit cmnd
This is really two separate commands.  The atomic form is an
attention changing command.  The current expression becomes the
nth form from the end of the old current expression.  That is,
-1 specifies the last element, -2 the second from last, etc.

The list form of the command is a structure modification command.
This command inserts exp1 thru expn (at least one expi must be
present) before the nth element (counting from the BEGINNING)
of the current expression.  That is, -1 inserts before the
first element, -2 before the second, etc.


(NEX com)						edit cmnd
NEX							edit cmnd
This command is equivalent to (BELOW com) followed by NX.  That
is, it does repeated 0s until a current expression matching
com is found.  It then backs off by one 0 and does a NX.

The atomic form of the command is equivalent to (NEX _).  This
is useful if the user is doing repeated (NEX x)s.  He can
MARK at x and then use the atomic form.

(NTH loc)						edit cmnd
This command effectively performs (LCL loc), (BELOW <), UP.
The net effect is to search the current expression only for the
form specified by the location specification loc.  From there,
return to the initial level and set the current expression to
be the tail whose first element contains the form specified by
loc at any level.

NX							edit cmnd
(NX n)							edit cmnd
The atomic form of this command makes the current expression the
expression following the present current expression (at the
same level).  

The list form of the command is equivalent to n (an integer number)
repetitions of NX.  If an error occurs (e.g., if there are not
n expressions following the current expression), the current
expression is unchanged.

OK							edit cmnd
This command causes normal exit from the editor.

The state of the edit will be saved on property LASTVALUE of the
atom EDIT.  If the next form edited is the same, the edit will
be restored.  That is, it will be (with the exception of a 
BLOCK on the undo-list) as though the editor had never been
exited.

It is possible to save edit states for more than one form by
exiting from the editor via the SAVE command.

(ORF pat1 pat2 ... patn)				edit cmnd
This command searches the current expression, in print order,
for the first occurrence of any form which matches one of the
pati.  When found, an UP is executed, and the current expression
becomes the expression so specified.  This command is equivalent
to (F (*ANY* pat1 pat2 ... patn) N).  Note that the top level
check is not performed.

(ORR coms1 coms2 ... comsn)				edit cmnd
This command operates in the following manner.  Each comsi is a
list of edit commands.  ORR first executes coms1.  If no error
occurs, ORR terminates, leaving the current expression as it
was at the end of executing coms1.  Otherwise, it restores the
current expression to what it was on entry and repeats this
operation on coms2, etc.  If no comsi is successfully executed
without error, ORR generates an error and the current expression
is unchanged.

P							edit cmnd
(P n1)							edit cmnd
(P n1 n2)						edit cmnd
This command prints the current expression.  The atomic form of
the command prints the current expression to a depth of 2.
More deeply nested forms are printed as &.

The second form of the command, (P n1) prints the n1st element of
the current expression to a depth of 2.  The argument, n1, need
not be an integer.  It may be a general location specification.
The NTH command is used in the search, so that the expression
printed will be the first element of the current expression
which contains the desired form at any level.

The third form of the command prints the n1st element of the
current expression to a depth of n2.  Again, n1 may be a general
location specification.

If n1 is 0, the current expression is printed.

Many of the editor commands, particularly those which search,
take as an argument a pattern (abbreviated pat).  A pattern
may be any combination of literal list structure and special
pattern elements.  

The special elements are as follows.
	& - this matches any single element.
	*ANY* - if (CAR pat) is the atom *ANY*, then (CDR pat)
		must be a list of patterns.  Pat matches any 
		form which matches any of the patterns in (CDR pat).
	@ - if an element of pat is a literal atom whose last 
		character is @, then that element matches any
		literal atom whose initial characters match the
		initial characters of the element.  That is,
		VER@ matches VERYLONGATOM.
	-- - this matches any tail of a list or any interior
		segment of a list.
	== - if (CAR pat) is ==, then pat matches X iff (CDR pat)
		is EQ to X.
	::: - if pat begins with :::, the CDR of pat is matched
		against tails of the expression.

n							edit cmnd
(n exp1 exp2 ... expn)					edit cmnd
This command, a strictly positive integer n, is really two
commands.  The atomic form of the command is an attention-
changing command.  The current expression becomes the nth
element of the current expression.

The list form of the command is a structure modification command.
It replaces the nth element of the current  expression by the
forms exp1 thru expn.  If no forms are given, then the nth element
of the current expression is deleted.

PP							edit cmnd
This command pretty-prints the current expression.

(R exp1 exp2)						edit cmnd
This command replaces all occurrences of exp1 by exp2 in the
current expression.  

Note that exp1 may be either the literal s-expression to be
replaced, or it may be an edit pattern.  If a pattern is given,
the form which first matches that pattern will be replaced
throughout.  All forms which match the pattern will NOT be
replaced.

REPACK							edit cmnd
(REPACK loc)						edit cmnd
This command allows the editing of long strings (or atom names)
one character at a time.  REPACK calls the editor recursively
on UNPACK of the specified atom.  (In the atomic form of the
command, the current expression is used unless it is a list;
then, the first element is used.  In the list form of the
command, the form specified by the location specification is
treated in the same way.)  If the lower editor is exited via
OK, the result is repacked and replaces the original atom.
If STOP is used, no replacement is done.  The new atom is
always printed.

(RI n1 n2)						edit cmnd
This command moves a right parenthesis.  The paren is moved from
the end of the the n1st element of the current expression to after 
the n2nd element of the n1st element.  Remaining elements of the
n1st element are raised to the top level of the current expression.

The arguments, n1 and n2, are normally integers.  However, because
the NTH command is used in the search, they may be any location
specifications.  The expressions referenced will be the first
element of the current expression in which the specified form
is found at any level, and the first element of that expression
in which the form specified by n2 is found at any level.

(RO n)							edit cmnd
This command moves the right parenthesis from the end of the nth
element of the current expression to the end of the current 
expression.  All elements following the nth are moved inside
the nth element.

Because the NTH command is used for the search, the argument n,
which is normally an integer, may be any location specification.
The expression referenced is the first element of the current
expression in which the specified form is found at any depth.

(S var loc)						edit cmnd
This command sets (via SETQ) the variable whose name is var to
the current expression after executing the location specification
loc.  The current expression is not changed.

SAVE							edit cmnd
This command exits normally from the editor.  The state of the
edit is saved on the property EDIT-SAVE of the atom being edited.
When the same atom is next edited, the state of the edit will
be restored and (with the exception of a BLOCK on the undo-list)
it will be as if the editor had never been exited.  It is not
necessary to use the SAVE command if only a single atom is being
edited.  See the OK command.

(SECOND loc)						edit cmnd
This command changes the current expression to what it would be
after the location specification loc is executed twice.  The
current expression is unchanged if either execution of loc fails.

STOP							edit cmnd
This command exits abnormally from the editor.  This command is
useful mainly in conjunction with TTY: commands which the user
wishes to abort.  For example, if the user is executing
	(MOVE 3 TO AFTER COND TTY:),
and he exits from the lower editor via OK, the MOVE command
will complete its operation.  If, on the other hand, the user
exits via STOP, TTY: will produce an error and MOVE will abort.

(SW n1 n2)						edit cmnd
This command swaps the n1st and n2nd elements of the current
expression.  The arguments are normally but not necessarily 
integers.  SW uses NTH to perform the search, so that any
location specifiations may be used.  In each case, the first element
of the current expression which contains the specified form at any
depth will be used.

TEST							edit cmnd
This command adds an undo-block to the undo-list.  This block
limits the scope of UNDO and !UNDO commands to changes made
after the block was inserted.  The block may be removed via
UNBLOCK.

(THIRD loc)						edit cmnd
This command executes the location specification loc three times.
It is equivalent to three repetitions of (LC loc).  Note, however,
that if any of the executions causes an editor error, the current
expression remains unchanged.

(loc1 THRU loc2)					edit cmnd
This command makes the current expression the segment from the
form specified by loc1 thru (including) the form specified by
loc2.  It is equivalent to (LC loc1), UP, (BI 1 loc2), 1.
Thus, it makes a single element of the specified elements and
makes that the current expression.  

This command is meant for use in the location specifications
given to the DELETE, EMBED, EXTRACT and REPLACE commands, and
is not particularly useful by itself.  Use of THRU with these
commands sets a special flag so that the editor removes the
extra set of parens added by THRU.

(loc1 TO loc2)						edit cmnd
This command makes the current expression the segment from the
form specified by loc1 up to (but not including) the form specified
by loc2.  It is equivalent to (LC loc1), UP, (BI 1 loc), (RI 1 -2),
1.  Thus, it makes a single element of the specified elements and
makes that the current expression.

This command is meant for use in the location specifications
given to the DELETE, EMBED, EXTRACT and REPLACE commands, and is
not particularly useful by itself.  Use of TO with these commands
sets a special flag so that the editor removes the extra set of
parens added by TO.

TTY:							edit cmnd
This command calls the editor recursively, invoking a 'lower editor.'
The user may execute any and all edit commands in this lower editor.
The TTY: command terminates when the lower editor is exited via
OK or STOP.

The form being edited in the lower editor is the same as that being
edited in the upper editor.  Upon entry, the current expression in
the lower is the same as that in the upper editor.

UNBLOCK							edit cmnd
This command removes an undo-block from the undo-list, allowing
UNDO and !UNDO to operate on changes which were made before the
block was inserted.

Blocks may be inserted by exiting from the editor and by the TEST
command.

UNDO							edit cmnd
UNDO com						edit cmnd
This command udoes editing changes.  All editing changes are
undoable, provided that the information is available to the 
editor.  (The necessary information is always available, unless
several forms are being edited and the SAVE command is not
used.)  Changes made in the current editing session are ALWAYS
undoable.  

The first form of the command undoes the most recent change.
Note, however, that UNDO and !UNDO changes are skipped, even
though they are themselves undoable.

The second form of the command allows the user to undo an
arbitrary command, not necessarily the most recent.  UNDO
and !UNDO may also be undone in this manner.

UP							edit cmnd
If the current expression is a tail of the next higher expression,
UP has no effect.  Otherwise, the current expression becomes the
form whose first element is the old current expression.

(XTR loc)						edit cmnd
This command replaces the current expression by one of its
subexpressions.  The location specification, loc, gives the
form to be used.  Note that only the current expression is
searched.  If the current expression is a tail, the command
operates on the first element of the tail.

0							edit cmnd
This command makes the current expression the next higher 
expression.  This usually, but not always, corresponds to
returning to the next higher left parenthesis.  This command
is, in some sense, the inverse of the POS-INTEGER and NEG-
INTEGER atomic commands.

(## com1 com2 ... comn)						fsubr
The value of this fsubr, useful mainly in macros, is the
expression which would be current after executing all of
the comi in sequence.  The current expression is not changed.

Commands in which this fsubr might be used (e.g., CHANGE,
INSERT and REPLACE) make special checks and use a copy
of the expression returned.

^							edit cmnd
This command makes the top level expression the current expression.

?							edit cmnd
This command prints the current expression to a level of 100.
It is equivalent to (P 0 100).

??							edit cmnd
This command displays the entries on the undo-list.

_							edit cmnd
This command returns to the position indicated by the most
recent MARK command.  The MARK is not removed.

(_ pat)							edit cmnd
This command ascends (does repeated 0s), testing the current
expression at each ascent for a match with pat.  The current
expression becomes the first form to match.  If pattern is
atomic, it is matched with the first element of each expression;
otherwise, it is matched against the entire form.

__							edit cmnd
This command returns to the position indicated by the most
recent MARK command and removes the MARK.

(: exp1 exp2 ... expn)					edit cmnd
(:)							edit cmnd
This command replaces the current expression by the forms exp1
thru expn.  If no forms are given (as in the second form of the
command), the current expression is deleted.

(pat :: loc)						edit cmnd
This command sets the current expression to the first form
(in print order) which matches pat and contains the form
specified by the location specification loc at any level.
The command is equivalent to (F pat N), (LCL loc), (_ pat).

\							edit cmnd
This command returns to the expression which was current before
the last 'big jump.'  Big jumps are caused by these commands:
^, _, __, !NX, all commands which perform a search or use a
location specification, \ itself, and \P.  NOTE: \ is shift-L
on a teletype.

\P							edit cmnd
This command returns to the expression which was current before
the last print operation (P, PP or ?).  Only the two most recent
locations are saved.  NOTE: \ is shift-L on a teletype.

!NX							edit cmnd
This command makes the next expression at a higher level the
current expression.  That is, it goes thru any number of right
parentheses to get to the next expression.


!UNDO							edit cmnd
This command undoes all changes made in the current editing session
(back to the most recent block).  All changes are undoable.  

Blocks may be inserted by exiting the editor or by the TEST
command.  They may be removed with the UNBLOCK command.

!0							edit cmnd
This command does repeated 0s until it reaches an expression which
is not a tail of the next higher expression.  That expression becomes
the new current expression.  That is, this command returns to
the next higher left parenthesis, regardless of intervening tails."