### 90.3 Characters

Characters are strings of length 1.

Function: adjust_external_format ()

  Prints information about the current external format of the Lisp reader and in case the external format encoding differs from the encoding of the application which runs Maxima `adjust_external_format` tries to adjust the encoding or prints some help or instruction. `adjust_external_format` returns `true` when the external format has been changed and `false` otherwise.

  Functions like cint, unicode, octets_to_string and string_to_octets need UTF-8 as the external format of the Lisp reader to work properly over the full range of Unicode characters.

  Examples (Maxima on Windows, March 2016): Using `adjust_external_format` when the default external format is not equal to the encoding provided by the application.

  1. Command line Maxima

  In case a terminal session is preferred it is recommended to use Maxima compiled with SBCL. Here Unicode support is provided by default and calls to `adjust_external_format` are unnecessary.

  If Maxima is compiled with CLISP or GCL it is recommended to change the terminal encoding from CP850 to CP1252. `adjust_external_format` prints some help.

  CCL reads UTF-8 while the terminal input is CP850 by default. CP1252 is not supported by CCL. `adjust_external_format` prints instructions for changing the terminal encoding and external format both to iso-8859-1.

  2. wxMaxima

  In wxMaxima SBCL reads CP1252 by default but the input from the application is UTF-8 encoded. Adjustment is needed.

  Calling `adjust_external_format` and restarting Maxima permanently changes the default external format to UTF-8.

      (%i1)adjust_external_format();
      The line
      (setf sb-impl::*default-external-format* :utf-8)
      has been appended to the init file
      C:/Users/Username/.sbclrc
      Please restart Maxima to set the external format to UTF-8.
      (%i1) false

  Restarting Maxima.

      (%i1) adjust_external_format();
      The external format is currently UTF-8
      and has not been changed.
      (%i1) false

  Categories:Package stringproc ·

Function: alphacharp (char)

  Returns `true` if char is an alphabetic character.

  To identify a non-US-ASCII character as an alphabetic character the underlying Lisp must provide full Unicode support. E.g. a German umlaut is detected as an alphabetic character with SBCL in GNU/Linux but not with GCL. (In Windows Maxima, when compiled with SBCL, must be set to UTF-8. See adjust_external_format for more.)

  Example: Examination of non-US-ASCII characters.

  The underlying Lisp (SBCL, GNU/Linux) is able to convert the typed character into a Lisp character and to examine.

      (%i1) alphacharp("ü");
      (%o1)                          true

  In GCL this is not possible. An error break occurs.

      (%i1) alphacharp("u");
      (%o1)                          true
      (%i2) alphacharp("ü");

      package stringproc: ü cannot be converted into a Lisp character.
       -- an error.

  Categories:Predicate functions ·Package stringproc ·

Function: alphanumericp (char)

  Returns `true` if char is an alphabetic character or a digit (only corresponding US-ASCII characters are regarded as digits).

  Note: See remarks on alphacharp.

  Categories:Predicate functions ·Package stringproc ·

Function: ascii (int)

  Returns the US-ASCII character corresponding to the integer int which has to be less than `128`.

  See unicode for converting code points larger than `127`.

  Examples:

      (%i1) for n from 0 thru 127 do (
              ch: ascii(n),
              if alphacharp(ch) then sprint(ch),
              if n = 96 then newline() )$
      A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
      a b c d e f g h i j k l m n o p q r s t u v w x y z

  Categories:Package stringproc ·

Function: cequal (char_1, char_2)

  Returns `true` if char_1 and char_2 are the same character.

  Categories:Predicate functions ·Package stringproc ·

Function: cequalignore (char_1, char_2)

  Like `cequal` but ignores case which is only possible for non-US-ASCII characters when the underlying Lisp is able to recognize a character as an alphabetic character. See remarks on alphacharp.

  Categories:Predicate functions ·Package stringproc ·

Function: cgreaterp (char_1, char_2)

  Returns `true` if the code point of char_1 is greater than the code point of char_2.

  Categories:Predicate functions ·Package stringproc ·

Function: cgreaterpignore (char_1, char_2)

  Like `cgreaterp` but ignores case which is only possible for non-US-ASCII characters when the underlying Lisp is able to recognize a character as an alphabetic character. See remarks on alphacharp.

  Categories:Predicate functions ·Package stringproc ·

Function: charp (obj)

  Returns `true` if obj is a Maxima-character. See introduction for example.

  Categories:Predicate functions ·Package stringproc ·

Function: cint (char)

  Returns the Unicode code point of char which must be a Maxima character, i.e. a string of length `1`.

  Examples: The hexadecimal code point of some characters (Maxima with SBCL on GNU/Linux).

      (%i1) obase: 16.$
      (%i2) map(cint, ["$","£","€"]);
      (%o2)                           [24, 0A3, 20AC]

  Warning: It is not possible to enter characters corresponding to code points larger than 16 bit in wxMaxima with SBCL on Windows when the external format has not been set to UTF-8. See adjust_external_format.

  CMUCL doesn’t process these characters as one character. `cint` then returns `false`. Converting a character to a code point via UTF-8-octets may serve as a workaround:

  `utf8_to_unicode(string_to_octets(character));`

  See utf8_to_unicode, string_to_octets.

  Categories:Package stringproc ·

Function: clessp (char_1, char_2)

  Returns `true` if the code point of char_1 is less than the code point of char_2.

  Categories:Predicate functions ·Package stringproc ·

Function: clesspignore (char_1, char_2)

  Like `clessp` but ignores case which is only possible for non-US-ASCII characters when the underlying Lisp is able to recognize a character as an alphabetic character. See remarks on alphacharp.

  Categories:Predicate functions ·Package stringproc ·

Function: constituent (char)

  Returns `true` if char is a graphic character but not a space character. A graphic character is a character one can see, plus the space character. (`constituent` is defined by Paul Graham. See Paul Graham, ANSI Common Lisp, 1996, page 67.)

      (%i1) for n from 0 thru 255 do (
      tmp: ascii(n), if constituent(tmp) then sprint(tmp) )$
      ! " #  %  ' ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < = > ? @ A B
      C D E F G H I J K L M N O P Q R S T U V W X Y Z [ \ ] ^ _ ` a b c
      d e f g h i j k l m n o p q r s t u v w x y z { | } ~

  Categories:Predicate functions ·Package stringproc ·

Function: digitcharp (char)

  Returns `true` if char is a digit where only the corresponding US-ASCII-character is regarded as a digit.

  Categories:Predicate functions ·Package stringproc ·

Function: lowercasep (char)

  Returns `true` if char is a lowercase character.

  Note: See remarks on alphacharp.

  Categories:Predicate functions ·Package stringproc ·

Variable: newline

  The newline character (ASCII-character 10).

  Categories:Global variables ·Package stringproc ·

Variable: space

  The space character.

  Categories:Global variables ·Package stringproc ·

Variable: tab

  The tab character.

  Categories:Global variables ·Package stringproc ·

Function: unicode (arg)

  Returns the character defined by arg which might be a Unicode code point or a name string if the underlying Lisp provides full Unicode support.

  Example: Characters defined by hexadecimal code points (Maxima with SBCL on GNU/Linux).

      (%i1) ibase: 16.$
      (%i2) map(unicode, [24, 0A3, 20AC]);
      (%o2)                            [$, £, €]

  Warning: In wxMaxima with SBCL on Windows it is not possible to convert code points larger than 16 bit to characters when the external format has not been set to UTF-8. See adjust_external_format for more information.

  CMUCL doesn’t process code points larger than 16 bit. In these cases `unicode` returns `false`. Converting a code point to a character via UTF-8 octets may serve as a workaround:

  `octets_to_string(unicode_to_utf8(code_point));`

  See octets_to_string, unicode_to_utf8.

  In case the underlying Lisp provides full Unicode support the character might be specified by its name. The following is possible in ECL, CLISP and SBCL, where in SBCL on Windows the external format has to be set to UTF-8. `unicode(name)` is supported by CMUCL too but again limited to 16 bit characters.

  The string argument to `unicode` is basically the same string returned by `printf` using the "~@c" specifier. But as shown below the prefix "#\" must be omitted. Underlines might be replaced by spaces and uppercase letters by lowercase ones.

  Example (continued): Characters defined by names (Maxima with SBCL on GNU/Linux).

      (%i3) printf(false, "~@c", unicode(0DF));
      (%o3)                    #\LATIN_SMALL_LETTER_SHARP_S
      (%i4) unicode("LATIN_SMALL_LETTER_SHARP_S");
      (%o4)                                  ß
      (%i5) unicode("Latin small letter sharp s");
      (%o5)                                  ß

  Categories:Package stringproc ·

Function: unicode_to_utf8 (code_point)

  Returns a list containing the UTF-8 code corresponding to the Unicode code_point.

  Examples: Converting Unicode code points to UTF-8 and vice versa.

      (%i1) ibase: obase: 16.$
      (%i2) map(cint, ["$","£","€"]);
      (%o2)                           [24, 0A3, 20AC]
      (%i3) map(unicode_to_utf8, %);
      (%o3)                 [[24], [0C2, 0A3], [0E2, 82, 0AC]]
      (%i4) map(utf8_to_unicode, %);
      (%o4)                           [24, 0A3, 20AC]

  Categories:Package stringproc ·

Function: uppercasep (char)

  Returns `true` if char is an uppercase character.

  Note: See remarks on alphacharp.

  Categories:Predicate functions ·Package stringproc ·

Variable: us_ascii_only

  This option variable affects Maxima when the character encoding provided by the application which runs Maxima is UTF-8 but the external format of the Lisp reader is not equal to UTF-8.

  On GNU/Linux this is true when Maxima is built with GCL and on Windows in wxMaxima with GCL- and SBCL-builds. With SBCL it is recommended to change the external format to UTF-8. Setting `us_ascii_only` is unnecessary then. See adjust_external_format for details.

  `us_ascii_only` is `false` by default. Maxima itself then (i.e. in the above described situation) parses the UTF-8 encoding.

  When `us_ascii_only` is set to `true` it is assumed that all strings used as arguments to string processing functions do not contain Non-US-ASCII characters. Given that promise, Maxima avoids parsing UTF-8 and strings can be processed more efficiently.

  Categories:Global variables ·Package stringproc ·

Function: utf8_to_unicode (list)

  Returns a Unicode code point corresponding to the list which must contain the UTF-8 encoding of a single character.

  Examples: See unicode_to_utf8.

  Categories:Package stringproc ·