File psl-1983/3-1/doc/nmode/nm-programs.ibm artifact 302d780ee2 part of check-in 955d0a90a7


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          201/NMODE Manual (Editing Programs)                                  Page 20-1


          202/20.  Editing Programs

            201/Special features for editing lisp programs include automatic indentation,
          parenthesis  matching,  and  the  ability  to  move  over  and  kill  balanced
          expressions.

          Lisp mode defines paragraphs to be separated only by blank lines and page
          boundaries.    This  makes  the  paragraph  commands  useful  for  editing
          programs.  See Section 13.2 [Paragraphs], page 2.

          Moving over words is useful for editing programs as well as text.  See
          Section 13.1 [Words], page 1.

          202/20.1  Major Modes

            201/NMODE has many different 202/major modes201/.  Two such modes are Text mode
          and Lisp mode.  Each of these customizes NMODE, one for text, the other for
          Lisp programs.  The major modes are mutually exclusive, and one major mode
          is current at any time.  When at top level, NMODE always says in the mode
          line which major mode you are in.  These modes tell NMODE to change the
          meanings of a few commands to become more specifically adapted to the
          language being edited.  Most commands remain unchanged; the ones which
          usually change are Tab, Backspace, and Linefeed.  In addition, a few special
          move and mark commands are turned on in Lisp mode which are not available
          in text mode.

            Selecting a new major mode can be done with a M-X command.  For example
          M-X Text Mode (203/text-mode-command201/) enters text mode and M-X Lisp Mode
          (203/lisp-mode-command201/) enters lisp mode.  As can be seen from these examples,
          some major mode's names are the same as the invocations of the functions to
          select those modes.

            Often NMODE enters the correct major mode for a file simply based on the
          file's extension, and you do not have to worry about selecting a mode.

            Lisp mode specifies that only blank lines separate paragraphs.  This is so
          that the paragraph commands remain useful.

          202/20.2  Indentation Commands for Code

                  201/Tab        Indents current line.
                  Linefeed    Equivalent to Return followed by Tab.
                  M-^        Joins two lines, leaving one space between if appropriate.
                  C-M-O     Split the current line.
                  M-\        Deletes all spaces and tabs around point.
                  M-M        Moves to the first nonblank character on the line.

            Most programming languages have some indentation convention.  For Lisp
          code, lines are indented according to their nesting in parentheses.

            Whatever the language, to indent a line, use the Tab command.  Each major
          mode defines this command to perform the sort of indentation appropriate for
          the particular language.  In Lisp mode, Tab aligns the line according to its
          201/Page 20-2                    NMODE Manual (Indentation Commands for Code)


          depth in parentheses.  No matter where in the line you are when you type
          Tab, it aligns the line as a whole.

            The command Linefeed (203/indent-new-line-command201/) does a Return and then
          does a Tab on the next line.  Thus, Linefeed at the end of the line makes a
          following blank line and supplies it with the usual amount of indentation.
          Linefeed in the middle of a line breaks the line and supplies the usual
          indentation in front of the new line.


            The inverse of Linefeed is Meta-^ or C-M-^ (203/delete-indentation-command201/).
          This command deletes the indentation at the front of the current line, and the
          line separator as well.  They are replaced by a single space, or by no space
          if before a ")" or after a "(", or at the beginning of a line. With an
          argument, M-^ joins the current line and the 203/next 201/line, removing indentation
          at the front of the next line beforehand.  To delete just the indentation of a
          line,   go   to   the   beginning   of   the   line   and   use   Meta-\
          (203/delete-horizontal-space-command201/), which deletes all spaces and tabs around
          the cursor.

            Another command which affects indentation is C-M-O (203/split-line-command201/).
          It moves the rest of the current line, after point, down vertically.   It
          indents the new line so that the rest of the line winds up in the same column
          that it was in before the split.  If this command is given a positive argument,
          it adds enough empty lines between the old line and the new line that the
          total number of lines added equals the argument.  The command leaves point
          unchanged.

            To insert an indented line before the current one, do C-A, C-O, and then
          Tab.  To make an indented line after the current one, use C-E Linefeed.

            To  move  over  the  indentation  on  a  line,  use  Meta-M  or  C-M-M
          (203/back-to-indentation-command201/).  These commands move the cursor forward or
          back to the first nonblank character on the line.

          202/20.3  Automatic Display Of Matching Parentheses

            201/The NMODE parenthesis-matching feature is designed to show automatically
          how parentheses balance in text as it is typed in.   When this feature is
          enabled, after a close parenthesis or other close bracket character is inserted
          (using 203/insert-closing-bracket201/) the cursor automatically moves for an instant to
          the open bracket which balances the newly inserted character.  The cursor
          stays at the open parenthesis for a second before returning home, unless you
          type another command before the second is up.

            It is worth emphasizing that the location of point, the place where your
          type-in will be inserted, is not affected by the parenthesis matching feature.
          It stays after the close parenthesis, where it ought to be.  Only the cursor
          on the screen moves away and back.  You can type ahead freely as if the
          parenthesis display feature did not exist.  In fact, if you type fast enough,
          you won't see the cursor move.   You must pause after typing a close
          parenthesis to let the cursor move to the open parenthesis.
          201/NMODE Manual (Automatic Display Of Matching Parentheses)         Page 20-3


            An additional function is whether NMODE should warn you by ringing the
          bell if you type an unmatched close parenthesis.  NMODE will warn you if you
          are editing a language in which parentheses are paramount, such as Lisp, but
          will not do so for languages in which parentheses are not so crucial.

          202/20.4  Manipulating Comments

                  201/M-;        Insert comment.
                  M-Z        Fill a block of comments.

            There are two NMODE commands which affect comments.  First there is M-;
          (203/insert-comment-command201/), which jumps to the end of the current line and
          inserts a percent sign and a space, thus starting a comment.  Second, there
          is M-Z (203/fill-comment-command201/), which allows filling of blocks of comments.  It
          fills a paragraph using whatever text is adjacent to the current line and
          begins  with  the  same  sequence  of  blank  characters,  nonalphanumeric
          characters, and more blank characters as the current line.  As a result, it
          will fill all lines starting with " % ", for instance.  Notice that it will NOT do
          any filling if the current line differs in indentation from the rest of the
          paragraph of comments (i.e. if it is an indented first line).

          202/20.5  Lisp Mode

            201/Lisp's simple syntax makes it much easier for an editor to understand; as a
          result, NMODE can do more for Lisp, and with less work, than for any other
          language.

            Lisp programs should be edited in Lisp mode.  In this mode, Tab is defined
          to indent the current line according to the conventions of Lisp programming
          style.  It does not matter where in the line Tab is used; the effect on the
          line  is  the  same.    The  function  which  does  the  work  is  called
          203/lisp-tab-command201/.  Linefeed, as usual, does a Return and a Tab, so it moves
          to the next line and indents it.

            As in most modes where indentation is likely to vary from line to line,
          Backspace (203/delete-backward-hacking-tabs-command 201/in Lisp mode) is redefined
          to treat a tab as if it were the equivalent number of spaces.  This makes it
          possible to rub out indentation one position at a time without worrying
          whether it is made up of spaces or tabs.

            Paragraphs are defined to start only with blank lines so that the paragraph
          commands can be useful.  Auto Fill indents the new lines which it creates.
          Comments start with "%".

          202/20.5.1  Moving Over and Killing Lists and forms

                  201/C-M-F          Move Forward over form.
                  C-M-B         Move Backward over form.
                  C-M-K         Kill form forward.
                  C-M-Rubout    Kill form backward.
          201/Page 20-4           NMODE Manual (Moving Over and Killing Lists and forms)


                  C-M-U         Move Up and backward in list structure.
                  C-M-(          Same as C-M-U.
                  C-(            Same as C-M-U.
                  C-M-)          Move up and forward in list structure.
                  C-)            Same as C-M-).
                  C-M-D         Move Down and forward in list structure.
                  C-M-N         Move forward over a list.
                  C-M-P          Move backward over a list.
                  C-M-T         Transpose forms.
                  C-M-@          Put mark after form.
                  M-(            Put parentheses around next form(s).
                  M-)            Move past next close parenthesis and re-indent.

            By convention, NMODE commands that deal with balanced parentheses are
          usually Control-Meta- characters.  They tend to be analogous in function to
          their Control- and Meta- equivalents.  These commands are usually thought of
          as pertaining to Lisp, but can be useful with any language in which some
          sort of parentheses exist (including English).  They are, however, only
          defined in Lisp mode.

            To move forward over a form, use C-M-F (203/move-forward-form-command201/).  If
          the first significant character after point is an "(", C-M-F moves past the
          matching ")".  If the first character is a ")", C-M-F just moves past it.  If
          the character begins an atom, C-M-F moves to the end of the atom.  C-M-F
          with an argument repeats that operation the specified number of times; with a
          negative argument, it moves backward instead.

            The command C-M-B (203/move-backward-form-command201/) moves backward over a
          form;   it is like C-M-F with the argument's sign reversed.  If there are
          "'"-like characters in front of the form moved over, they are moved over as
          well.  Thus, with point after " 'FOO ", C-M-B leaves point before the "'",
          not before the "F".

            These two commands (and the commands in this section) know how to handle
          comments, string literals, and all other token syntax in (unaltered) PSL.
          NMODE makes one restriction: it will not handle string literals that extend
          over multiple lines.

            Two other commands move over lists instead of forms are often useful.
          They     are     C-M-N     (203/move-forward-list-command201/)     and     C-M-P
          (203/move-backward-list-command201/).  They act like C-M-F and C-M-B except that
          they don't stop on atoms; after moving over an atom, they move over the
          next expression, stopping after moving over a list.  With these commands,
          you can avoid stopping after all of the atomic arguments to a function.

            Killing   a   form   at   a   time   can   be   done   with   C-M-K
          (203/kill-forward-form-command201/) and  C-M-Rubout  (203/kill-backward-form-command201/)
          commands.   C-M-K kills the characters that C-M-F would move over, and
          C-M-Rubout kills what C-M-B would move over.

            C-M-F and C-M-B stay at the same level in parentheses, when that's
          possible.    To  move  203/up  201/one  (or  n)  levels,  use  C-M-(  or  C-M-)
          (203/backward-up-list 201/and 203/forward-up-list-command201/).  C-M-( moves backward up
          201/NMODE Manual (Moving Over and Killing Lists and forms)           Page 20-5


          past one containing "(".  C-M-) moves forward up past one containing ")".
          Given a positive argument, these commands move up the specified number of
          levels of parentheses.  C-M-U is another name for C-M-(, which is easier to
          type, especially on non-Meta keyboards.  If you use that name, it is useful
          to know that a negative argument makes the command move up forwards, like
          C-M-). C-M-( and C-M-) are also availible as C-( and C-), respectively,
          which are easier to type on the hp9836 keyboard.

            To move 203/down 201/in list structure, use C-M-D (203/down-list-command201/).  It is
          nearly the same as searching for a "(".

            A somewhat random-sounding command which is nevertheless easy to use is
          C-M-T (203/transpose-forms201/), which drags the previous form across the next
          one.  An argument serves as a repeat count, and a negative argument drags
          backwards (thus canceling out the effect of C-M-T with a positive argument).
          An argument of zero, rather than doing nothing, transposes the forms at the
          point and the mark.

            To  make  the  region  be  the  next  form  in  the  buffer,  use  C-M-@
          (203/mark-form-command201/) which sets mark at the same place that C-M-F would
          move to.   C-M-@ takes arguments like C-M-F.  In particular, a negative
          argument is useful for putting the mark at the beginning of the previous
          form.

            The      commands      M-(      (203/make-parens-command201/)      and     M-)
          (203/move-over-paren-command201/) are designed for a style of editing which keeps
          parentheses balanced at all times.  M-( inserts a pair of parentheses, either
          together as in "()", or, if given an argument, around the next several
          forms, and leaves point after the open parenthesis.   Instead of typing
          "(FOO)", you can type M-( FOO, which has the same effect except for
          leaving the cursor before the close parenthesis.  Then you type M-), which
          moves past the close parenthesis, deleting any indentation preceding it (in
          this example there is none), and indenting with Linefeed after it.

          202/20.5.2  Commands for Manipulating Defuns

                  201/C-M-[, C-M-A  Move to beginning of defun.
                  C-M-], C-M-E  Move to end of defun.
                  C-M-H         Put region around whole defun.

            For historical reasons, an expression at the top level in the buffer is called
          a 202/defun201/, regardless of what function is actually called by the expression.

            One might imagine that NMODE finds defuns by moving upward a level of
          parentheses until there were no more levels to go up.  This would require
          scanning all the way back to the beginning of the file.  To speed up the
          operation, NMODE assumes that any "(" in column 0 is the start of a defun.
          This heuristic is nearly always right and avoids the costly scan.

            The commands to move to the beginning and end of the current defun are
          C-M-[ (203/move-backward-defun-command201/) and C-M-] (203/end-of-defun-command201/).
          Alternate names for these two commands are C-M-A for C-M-[ and C-M-E for
          C-M-].  The alternate names are easier to type on many non-Meta keyboards.
          201/Page 20-6                 NMODE Manual (Commands for Manipulating Defuns)


            If   you   wish   to   operate   on   the   current   defun,   use  C-M-H
          (203/mark-defun-command201/) which puts point at the beginning and mark at the end
          of the current or next defun.

          202/20.6  Lisp Grinding

            201/The best way to keep Lisp code properly indented ("ground") is to use
          NMODE to re-indent it when it is changed.  NMODE has commands to indent
          properly either a single line, a specified number of lines, or all of the lines
          inside a single form.

                  Tab        In Lisp mode, re-indents line according to parenthesis
                              depth.
                  Linefeed    Equivalent to Return followed by Tab.
                  M-^        Join  two  lines,  leaving  one  space  between  them  if
                              appropriate.
                  C-M-Q     Re-indent all the lines within one list.

            The basic indentation function is 203/lisp-tab-command201/, which gives the current
          line the correct indentation as determined from the previous lines' indentation
          and parenthesis structure.  This function is placed on Tab in Lisp mode (Use
          Meta-Tab or C-Q Tab to insert a tab).  If executed at the beginning of a
          line, it leaves point after the indentation; when given inside the text on the
          line, it leaves point fixed with respect to the characters around it.

            When   entering   a   large   amount   of   new   code,   use   Linefeed
          (203/indent-new-line-command201/), which is equivalent to a Return followed by a
          Tab.  In Lisp mode, a Linefeed creates or moves down onto a blank line, and
          then gives it the appropriate indentation.

            To join two lines together, use the Meta-^ or Control-Meta-^ command
          (203/delete-indentation-command201/),  which  is  approximately  the  opposite  of
          Linefeed.  It deletes any spaces and tabs at the front of the current line,
          and then deletes the line separator before the line.  A single space is then
          inserted, if NMODE thinks that one is needed there.  Spaces are not needed
          before a close parenthesis, or after an open parenthesis.

            If you are dissatisfied about where Tab indents the second and later lines
          of an form, you can override it.  If you alter the indentation of one of the
          lines yourself, then Tab will indent successive lines of the same list to be
          underneath it.   This is the right thing for functions which Tab indents
          unaesthetically.

            When you wish to re-indent code which has been altered or moved to a
          different level in the list structure, you have several commands available.
          You can re-indent a specific number of lines by giving the ordinary indent
          command (Tab, in Lisp mode) an argument.  This indents as many lines as
          you say and moves to the line following them. Thus, if you underestimate,
          you can repeat the process later.

            You can re-indent the contents of a single form by positioning point before
          the beginning of it and typing Control-Meta-Q (203/lisp-indent-sexpr201/).  The line
          the form starts on is not re-indented;  thus, only the relative indentation
          201/NMODE Manual (Lisp Grinding)                                      Page 20-7


          with in the form, and not its position, is changed.  To correct the position
          as well, type a Tab before the C-M-Q.

            Another way to specify the range to be re-indented is with point and mark.
          The command C-M-\ (203/lisp-indent-region-command201/) applies Tab to every line
          whose first character is between point and mark.  In Lisp mode, this does a
          Lisp indent.

            The standard pattern of indentation is as follows: the second line of the
          expression is indented under the first argument, if that is on the same line
          as the beginning of the expression; otherwise, the second line is indented
          two spaces more than the entire expression.  Each following line is indented
          under the previous line whose nesting depth is the same.

          202/20.7  Lisp Language Interface

            201/The following section contains many commands starting with "Lisp-".  This
          prefix is equivalent to C-], but can sometimes be typed using a soft key.

          202/20.7.1  Evaluation

            201/NMODE contains a number of facilities to allow the user to  use  the
          underlying LISP language.  In addition to editing and pretty-printing LISP
          expressions with the commands in the preceding sections, the user can
          execute the LISP expressions in the buffer.

                  Lisp-D         Execute the current Defun.
                  Lisp-E         Execute the form starting on this line.
                  Lisp-Y         Yanks the last output into current buffer.

          Lisp-D (203/execute-defun-command201/) causes the Lisp reader to read and evaluate
          the current defun.  If there is no current defun, the Lisp reader will read a
          form starting at the current location.  We arrange for output to be appended
          to the end of the output buffer.  The mark is set at the current location in
          the input buffer, in case user wants to go back.

          Lisp-E (203/execute-form-command201/) causes the Lisp reader to read and evaluate a
          form starting at the beginning of the current line.  We arrange for output to
          be appended to the end of the output buffer.  The mark is set at the current
          location in the input buffer, in case user wants to go back.

          Lisp-Y (203/yank-last-output-command201/) copies the last piece of output from the
          output buffer back into the current buffer, allowing it to be added to some
          code or text within the current buffer.


          202/20.7.2  Debugging

            201/The commands of the last subsection allow one to use the underlying LISP,
          provided that no errors  occur  in  the  evaluation  of  expressions.   The
          commands of this subsection allow recovery from errors in evaluations.  When
          an error occurs, one enters a "break loop".   This is indicated by the
          presence of more than one angle bracket on the lisp prompt at the right hand
          201/Page 20-8                                         NMODE Manual (Debugging)


          side of the mode line under the output buffer.  When one is in a break loop,
          one can still evaluate lisp expressions.  Additional errors at this point will
          wrap additional break loops around the current one.  Commands available in
          break loops include:

                  Lisp-A         Abort break loops.
                  Lisp-Q         Quit current break loop.
                  Lisp-B         Backtrace function calls.
                  Lisp-C         Continue execution.
                  Lisp-R         Retry expression.
                  Lisp-?          Help command

            Lisp-A (203/lisp-abort-command201/) will pop out of an arbitrarily deep break loop.
          Lisp-Q (203/lisp-quit-command201/) exits the current break loop. It only pops up one
          level, unlike abort.

          Lisp-B (203/lisp-backtrace-command201/) lists all the function calls on the stack. The
          most recently invoked function is listed first.  It is a good way to see how
          the  offending  expression  got  generated.   Unfortunately,  many  internal
          functions of Lisp and NMODE are shown, so the list may get somewhat
          cluttered.

          Lisp-C (203/lisp-continue-command201/) causes the expression last printed to be
          returned as the value of the offending expression.  This allows a user to
          recover from a low level error in an involved calculation if they know what
          should have been returned by the offending expression.  This is also often
          useful as an automatic stub: If an expression  containing  an  undefined
          function is evaluated, a Break loop is entered, and this may be used to
          return the value of the function call.

          Lisp-R (203/lisp-retry-command201/) tries to evaluate the offending expression again,
          and to continue the computation.   This is often useful after defining a
          missing function, or assigning a value to a variable.

          Lisp-? (203/lisp-help-command201/) lists the lisp commands available.  When in a
          break loop it prints:
              "Lisp break commands: Q-quit;A-abort;R-retry;C-continue;B-backtrace"
          Otherwise it prints:
              "Lisp  commands:  E-execute  form;Y-yank  last  output;L-invoke  Lisp
          Listener"

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