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1.1 root 1: Differences between GNU Emacs and CCA Emacs.
2: Copyright (c) 1985 Richard M. Stallman
3:
4: Permission is granted to anyone to make or distribute verbatim copies
5: of this document as received, in any medium, provided that the
6: copyright notice and permission notice are preserved,
7: and that the distributor grants the recipient permission
8: for further redistribution as permitted by this notice.
9:
10: * GNU Emacs Lisp vs CCA Elisp.
11:
12: GNU Emacs Lisp does not have a distinction between Lisp functions
13: and Emacs functions, or between Lisp variables and Emacs variables.
14: The Lisp and the editor are integrated. A Lisp function defined
15: with defun is callable as an editor command if you put an
16: interactive calling spec in it; for example,
17: (defun forward-character (n)
18: (interactive "p")
19: (goto-char (+ (point) n)))
20: defines a function of one argument that moves point forward by
21: a specified number of characters. Programs could call this function,
22: as in (forward-character 6), or it could be assigned to a key,
23: in which case the "p" says to pass the prefix numeric arg as
24: the function's argument. As a result of this feature, you often
25: need not have two different functions, one to be called by programs
26: and another to read arguments from the user conveniently; the same
27: function can do both.
28:
29: CCA Elisp tries to be a subset of Common Lisp and tries to
30: have as many Common Lisp functions as possible (though it is still
31: only a small fraction of full Common Lisp). GNU Emacs Lisp
32: is somewhat similar to Common Lisp just because of my Maclisp
33: and Lisp Machine background, but it has several distinct incompatibilities
34: in both syntax and semantics. Also, I have not attempted to
35: provide many Common Lisp functions that you could write in Lisp,
36: or others that provide no new capability in the circumstances.
37:
38: GNU Emacs Lisp does not have packages, readtables, or character objects
39: (it uses integers to represent characters).
40:
41: On the other hand, windows, buffers, relocatable markers and processes
42: are first class objects in GNU Emacs Lisp. You can get information about them
43: and do things to them in a Lispy fashion. Not so in CCA Emacs.
44:
45: In GNU Emacs Lisp, you cannot open a file and read or write characters
46: or Lisp objects from it. This feature is painful to support, and
47: is not fundamentally necessary in an Emacs, because instead you
48: can read the file into a buffer, read or write characters or
49: Lisp objects in the buffer, and then write the buffer into the file.
50:
51: On the other hand, GNU Emacs Lisp does allow you to rename, delete, add
52: names to, and copy files; also to find out whether a file is a
53: directory, whether it is a symbolic link and to what name, whether
54: you can read it or write it, find out its directory component,
55: expand a relative pathname, find completions of a file name, etc.,
56: which you cannot do in CCA Elisp.
57:
58: GNU Emacs Lisp uses dynamic scope exclusively. This enables you to
59: bind variables which affect the execution of the editor, such as
60: indent-tabs-mode.
61:
62: GNU Emacs Lisp code is normally compiled into byte code. Most of the
63: standard editing commands are written in Lisp, and many are
64: dumped, pure, in the Emacs that users normally run.
65:
66: GNU Emacs allows you to interrupt a runaway Lisp program with
67: Control-g.
68:
69: * GNU Emacs Editing Advantages
70:
71: GNU Emacs is faster for many things, especially insertion of text
72: and file I/O.
73:
74: GNU Emacs allows you to undo more than just the last command
75: with the undo command (C-x u, or C-_). You can undo quite a ways back.
76: Undo information is separate for each buffer; changes in one buffer
77: do not affect your ability to undo in another buffer.
78:
79: GNU Emacs commands that want to display some output do so by putting
80: it in a buffer and displaying that buffer in a window. This
81: technique comes from Gosling Emacs. It has both advantages and
82: disadvantages when compared with the technique, copied by CCA Emacs
83: from my original Emacs which inherited it from TECO, of having "type
84: out" which appears on top of the text in the current window but
85: disappears automatically at the next input character.
86:
87: GNU Emacs does not use the concept of "subsystems". Instead, it uses
88: highly specialized major modes. For example, dired in GNU Emacs has
89: the same commands as dired does in other versions of Emacs, give or
90: take a few, but it is a major mode, not a subsystem. The advantage
91: of this is that you do not have to "exit" from dired and lose the
92: state of dired in order to edit files again. You can simply switch
93: to another buffer, and switch back to the dired buffer later. You
94: can also have several dired buffers, looking at different directories.
95:
96: It is still possible to write a subsystem--your own command loop--
97: in GNU Emacs, but it is not recommended, since writing a major mode
98: for a special buffer is better.
99:
100: Recursive edits are also rarely used, for the same reason: it is better
101: to make a new buffer and put it in a special major mode. Sending
102: mail is done this way.
103:
104: GNU Emacs expects everyone to use find-file (C-x C-f) for reading
105: in files; its C-x C-v command kills the current buffer and then finds
106: the specified file.
107:
108: As a result, users do not need to think about the complexities
109: of subsystems, recursive edits, and various ways to read in files
110: or what to do if a buffer contains changes to some other file.
111:
112: GNU Emacs uses its own format of tag table, made by the "etags"
113: program. This format makes finding a tag much faster.
114:
115: Dissociated Press is supported.
116:
117:
118: * GNU Emacs Editing Disadvantages.
119:
120: GNU Emacs does not display the location of the mark.
121:
122: GNU Emacs does not have a concept of numbers of buffers,
123: or a permanent ordering of buffers, or searching through multiple
124: buffers. The tags-search command provides a way to search
125: through several buffers automatically.
126:
127: GNU Emacs does not provide commands to visit files without
128: setting the buffer's default directory. Users can write such
129: commands in Lisp by copying the code of the standard file
130: visiting commands and modifying them.
131:
132: GNU Emacs does not support "plus options" in the command
133: arguments or in buffer-selection commands, except for line numbers.
134:
135: GNU Emacs does not support encryption. Down with security!
136:
137: GNU Emacs does not support replaying keystroke files,
138: and does not normally write keystroke files.
139:
140: GNU Emacs does not support the Life game.
141:
142:
143: * Neutral Differences
144:
145: GNU Emacs uses TAB, not ESC, to complete file names, buffer names,
146: command names, etc.
147:
148: GNU Emacs uses ESC to terminate searches, instead of
149: the C-d uses by CCA Emacs. (Actually, this character is controlled
150: by a parameter in GNU Emacs.) C-M-s in GNU Emacs is an interactive
151: regular expression search, but you can get to a noninteractive
152: one by typing ESC right after the C-M-s. GNU Emacs searches
153: never wrap around at beginning or end of buffer.
154:
155: In GNU Emacs, C-x s asks, for each modified file buffer, whether
156: to save it.
157:
158: GNU Emacs indicates line continuation with "\" and line
159: truncation (at either margin) with "$".
160:
161: The command to resume a tags-search or tags-query-replace in
162: GNU Emacs is Meta-Comma.
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