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comparison man/lispref/objects.texi @ 398:74fd4e045ea6 r21-2-29

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Import from CVS: tag r21-2-29
author cvs
date Mon, 13 Aug 2007 11:13:30 +0200
parents 7d59cb494b73
children 697ef44129c6
comparison
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397:f4aeb21a5bad 398:74fd4e045ea6
341 341
342 @xref{Numbers}, for more information. 342 @xref{Numbers}, for more information.
343 343
344 @node Character Type 344 @node Character Type
345 @subsection Character Type 345 @subsection Character Type
346 @cindex @sc{ASCII} character codes 346 @cindex @sc{ascii} character codes
347 @cindex char-int confoundance disease 347 @cindex char-int confoundance disease
348 348
349 In XEmacs version 19, and in all versions of FSF GNU Emacs, a 349 In XEmacs version 19, and in all versions of FSF GNU Emacs, a
350 @dfn{character} in XEmacs Lisp is nothing more than an integer. 350 @dfn{character} in XEmacs Lisp is nothing more than an integer.
351 This is yet another holdover from XEmacs Lisp's derivation from 351 This is yet another holdover from XEmacs Lisp's derivation from
352 vintage-1980 Lisps; modern versions of Lisp consider this equivalence 352 vintage-1980 Lisps; modern versions of Lisp consider this equivalence
353 a bad idea, and have separate character types. In XEmacs version 20, 353 a bad idea, and have separate character types. In XEmacs version 20,
354 the modern convention is followed, and characters are their own 354 the modern convention is followed, and characters are their own
355 primitive types. (This change was necessary in order for @sc{MULE}, 355 primitive types. (This change was necessary in order for @sc{mule},
356 i.e. Asian-language, support to be correctly implemented.) 356 i.e. Asian-language, support to be correctly implemented.)
357 357
358 Even in XEmacs version 20, remnants of the equivalence between 358 Even in XEmacs version 20, remnants of the equivalence between
359 characters and integers still exist; this is termed the @dfn{char-int 359 characters and integers still exist; this is termed the @dfn{char-int
360 confoundance disease}. In particular, many functions such as @code{eq}, 360 confoundance disease}. In particular, many functions such as @code{eq},
361 @code{equal}, and @code{memq} have equivalent functions (@code{old-eq}, 361 @code{equal}, and @code{memq} have equivalent functions (@code{old-eq},
362 @code{old-equal}, @code{old-memq}, etc.) that pretend like characters 362 @code{old-equal}, @code{old-memq}, etc.) that pretend like characters
363 are integers are the same. Byte code compiled under any version 19 363 are integers are the same. Byte code compiled under any version 19
364 Emacs will have all such functions mapped to their @code{old-} equivalents 364 Emacs will have all such functions mapped to their @code{old-} equivalents
365 when the byte code is read into XEmacs 20. This is to preserve 365 when the byte code is read into XEmacs 20. This is to preserve
366 compatibility -- Emacs 19 converts all constant characters to the equivalent 366 compatibility---Emacs 19 converts all constant characters to the equivalent
367 integer during byte-compilation, and thus there is no other way to preserve 367 integer during byte-compilation, and thus there is no other way to preserve
368 byte-code compatibility even if the code has specifically been written 368 byte-code compatibility even if the code has specifically been written
369 with the distinction between characters and integers in mind. 369 with the distinction between characters and integers in mind.
370 370
371 Every character has an equivalent integer, called the @dfn{character 371 Every character has an equivalent integer, called the @dfn{character
372 code}. For example, the character @kbd{A} is represented as the 372 code}. For example, the character @kbd{A} is represented as the
373 @w{integer 65}, following the standard @sc{ASCII} representation of 373 @w{integer 65}, following the standard @sc{ascii} representation of
374 characters. If XEmacs was not compiled with @sc{MULE} support, the 374 characters. If XEmacs was not compiled with @sc{mule} support, the
375 range of this integer will always be 0 to 255 -- eight bits, or one 375 range of this integer will always be 0 to 255---eight bits, or one
376 byte. (Integers outside this range are accepted but silently truncated; 376 byte. (Integers outside this range are accepted but silently truncated;
377 however, you should most decidedly @emph{not} rely on this, because it 377 however, you should most decidedly @emph{not} rely on this, because it
378 will not work under XEmacs with @sc{MULE} support.) When @sc{MULE} 378 will not work under XEmacs with @sc{mule} support.) When @sc{mule}
379 support is present, the range of character codes is much 379 support is present, the range of character codes is much
380 larger. (Currently, 19 bits are used.) 380 larger. (Currently, 19 bits are used.)
381 381
382 FSF GNU Emacs uses kludgy character codes above 255 to represent 382 FSF GNU Emacs uses kludgy character codes above 255 to represent
383 keyboard input of @sc{ASCII} characters in combination with certain 383 keyboard input of @sc{ascii} characters in combination with certain
384 modifiers. XEmacs does not use this (a more general mechanism is 384 modifiers. XEmacs does not use this (a more general mechanism is
385 used that does not distinguish between @sc{ASCII} keys and other 385 used that does not distinguish between @sc{ascii} keys and other
386 keys), so you will never find character codes above 255 in a 386 keys), so you will never find character codes above 255 in a
387 non-@sc{MULE} XEmacs. 387 non-@sc{mule} XEmacs.
388 388
389 Individual characters are not often used in programs. It is far more 389 Individual characters are not often used in programs. It is far more
390 common to work with @emph{strings}, which are sequences composed of 390 common to work with @emph{strings}, which are sequences composed of
391 characters. @xref{String Type}. 391 characters. @xref{String Type}.
392 392
504 character code). For example, @samp{?\M-A} stands for the character 504 character code). For example, @samp{?\M-A} stands for the character
505 with character code 193, or 128 plus 65. You should @emph{not} use this 505 with character code 193, or 128 plus 65. You should @emph{not} use this
506 syntax in your programs. It is a holdover of yet another confoundance 506 syntax in your programs. It is a holdover of yet another confoundance
507 disease from earlier Emacsen. (This was used to represent keyboard input 507 disease from earlier Emacsen. (This was used to represent keyboard input
508 with the @key{META} key set, thus the @samp{M}; however, it conflicts 508 with the @key{META} key set, thus the @samp{M}; however, it conflicts
509 with the legitimate @sc{ISO}-8859-1 interpretation of the character code. 509 with the legitimate @sc{iso}-8859-1 interpretation of the character code.
510 For example, character code 193 is a lowercase @samp{a} with an acute 510 For example, character code 193 is a lowercase @samp{a} with an acute
511 accent, in @sc{ISO}-8859-1.) 511 accent, in @sc{iso}-8859-1.)
512 512
513 @ignore @c None of this crap applies to XEmacs. 513 @ignore @c None of this crap applies to XEmacs.
514 For use in strings and buffers, you are limited to the control 514 For use in strings and buffers, you are limited to the control
515 characters that exist in @sc{ASCII}, but for keyboard input purposes, 515 characters that exist in @sc{ascii}, but for keyboard input purposes,
516 you can turn any character into a control character with @samp{C-}. The 516 you can turn any character into a control character with @samp{C-}. The
517 character codes for these non-@sc{ASCII} control characters include the 517 character codes for these non-@sc{ascii} control characters include the
518 @iftex 518 @iftex
519 $2^{26}$ 519 $2^{26}$
520 @end iftex 520 @end iftex
521 @ifinfo 521 @ifinfo
522 2**26 522 2**26
615 @cindex octal character code 615 @cindex octal character code
616 Finally, the most general read syntax consists of a question mark 616 Finally, the most general read syntax consists of a question mark
617 followed by a backslash and the character code in octal (up to three 617 followed by a backslash and the character code in octal (up to three
618 octal digits); thus, @samp{?\101} for the character @kbd{A}, 618 octal digits); thus, @samp{?\101} for the character @kbd{A},
619 @samp{?\001} for the character @kbd{C-a}, and @code{?\002} for the 619 @samp{?\001} for the character @kbd{C-a}, and @code{?\002} for the
620 character @kbd{C-b}. Although this syntax can represent any @sc{ASCII} 620 character @kbd{C-b}. Although this syntax can represent any @sc{ascii}
621 character, it is preferred only when the precise octal value is more 621 character, it is preferred only when the precise octal value is more
622 important than the @sc{ASCII} representation. 622 important than the @sc{ascii} representation.
623 623
624 @example 624 @example
625 @group 625 @group
626 ;; @r{Under XEmacs 20:} 626 ;; @r{Under XEmacs 20:}
627 ?\012 @result{} ?\n ?\n @result{} ?\n ?\C-j @result{} ?\n 627 ?\012 @result{} ?\n ?\n @result{} ?\n ?\C-j @result{} ?\n
1519 A @dfn{device} represents a single display on which frames exist. 1519 A @dfn{device} represents a single display on which frames exist.
1520 Normally, there is only one device object, but there may be more 1520 Normally, there is only one device object, but there may be more
1521 than one if XEmacs is being run on a multi-headed display (e.g. an 1521 than one if XEmacs is being run on a multi-headed display (e.g. an
1522 X server with attached color and mono screens) or if XEmacs is 1522 X server with attached color and mono screens) or if XEmacs is
1523 simultaneously driving frames attached to different consoles, e.g. 1523 simultaneously driving frames attached to different consoles, e.g.
1524 an X display and a @sc{TTY} connection. 1524 an X display and a @sc{tty} connection.
1525 1525
1526 Devices do not have a read syntax. They print in hash notation, 1526 Devices do not have a read syntax. They print in hash notation,
1527 giving the device's type, connection name, and a unique number assigned 1527 giving the device's type, connection name, and a unique number assigned
1528 at the time the device was created. 1528 at the time the device was created.
1529 1529
1542 1542
1543 A @dfn{console} represents a single keyboard to which devices 1543 A @dfn{console} represents a single keyboard to which devices
1544 (i.e. displays on which frames exist) are connected. Normally, there is 1544 (i.e. displays on which frames exist) are connected. Normally, there is
1545 only one console object, but there may be more than one if XEmacs is 1545 only one console object, but there may be more than one if XEmacs is
1546 simultaneously driving frames attached to different X servers and/or 1546 simultaneously driving frames attached to different X servers and/or
1547 @sc{TTY} connections. (XEmacs is capable of driving multiple X and 1547 @sc{tty} connections. (XEmacs is capable of driving multiple X and
1548 @sc{TTY} connections at the same time, and provides a robust mechanism 1548 @sc{tty} connections at the same time, and provides a robust mechanism
1549 for handling the differing display capabilities of such heterogeneous 1549 for handling the differing display capabilities of such heterogeneous
1550 environments. A buffer with embedded glyphs and multiple fonts and 1550 environments. A buffer with embedded glyphs and multiple fonts and
1551 colors, for example, will display reasonably if it simultaneously 1551 colors, for example, will display reasonably if it simultaneously
1552 appears on a frame on a color X display, a frame on a mono X display, 1552 appears on a frame on a color X display, a frame on a mono X display,
1553 and a frame on a @sc{TTY} connection.) 1553 and a frame on a @sc{tty} connection.)
1554 1554
1555 Consoles do not have a read syntax. They print in hash notation, 1555 Consoles do not have a read syntax. They print in hash notation,
1556 giving the console's type, connection name, and a unique number assigned 1556 giving the console's type, connection name, and a unique number assigned
1557 at the time the console was created. 1557 at the time the console was created.
1558 1558