string -- r7rs Type

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Sub-types tree

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• string-empty;
• string-not-empty:
  • path-string;

Super-types

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• (none);

Sub-types

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• string-empty;
• string-not-empty;

Sub-types recursive

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• path-string;

Referent definitions as input

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• syntax-error;
• string?;
• string-append;
• string-copy;
• string-copy!;
• string-fill!;
• substring;
• string=?;
• string<?;
• string>?;
• string<=?;
• string>=?;
• string-ci=?;
• string-ci<?;
• string-ci>?;
• string-ci<=?;
• string-ci>=?;
• string->list;
• string->vector;
• string-map;
• string-for-each;
• string->utf8;
• open-input-string;
• write-string;
• error;

Referent definitions as output

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• string-append;
• string-copy;
• substring;
• symbol->string;
• vector->string;
• utf8->string;
• get-output-string;
• error-object-message;

Referent definitions as output (recursive)

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• string;
• make-string;
• list->string;
• string-upcase;
• string-downcase;
• string-foldcase;
• number->string;

Note: These definitions produce an output that is a sub-type.

Predicate

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string?

Description

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Strings are sequences of characters. Strings are written as sequences of characters enclosed within quotation marks ("). Within a string literal, various escape sequences represent characters other than themselves. Escape sequences always start with a backslash (\):

• \a -- alarm, U+0007;
• \b -- backspace, U+0008;
• \t -- character tabulation, U+0009;
• \n -- linefeed, U+000A;
• \r -- return, U+000D;
• \" -- double quote, U+0022;
• \\ -- backslash, U+005C;
• \| -- vertical line, U+007C;
• \<intraline whitespace>*<line ending><intraline whitespace>* -- nothing
• \x<hex scalar value>; -- specified character (note the terminating semi-colon).

The result is unspecified if any other character in a string occurs after a backslash.

Except for a line ending, any character outside of an escape sequence stands for itself in the string literal. A line ending which is preceded by <intraline whitespace> expands to nothing (along with any trailing intraline whitespace), and can be used to indent strings for improved legibility. Any other line ending has the same effect as inserting a \n character into the string.

Examples:

"The word \"recursion\" has many meanings."
"Another example:\ntwo lines of text"
"Here's text \
   containing just one line"
"\x03B1; is named GREEK SMALL LETTER ALPHA."

The length of a string is the number of characters that it contains. This number is an exact, non-negative integer that is fixed when the string is created. The valid indexes of a string are the exact non-negative integers less than the length of the string. The first character of a string has index 0, the second has index 1, and so on.

Some of the procedures that operate on strings ignore the difference between upper and lower case. The names of the versions that ignore case end with -ci (for case insensitive).

Implementations may forbid certain characters from appearing in strings. However, with the exception of #\null, ASCII characters must not be forbidden. For example, an implementation might support the entire Unicode repertoire, but only allow characters U+0001 to U+00FF (the Latin-1 repertoire without #\null) in strings.

It is an error to pass such a forbidden character to make-string, string, string-set!, or string-fill!, as part of the list passed to list->string, or as part of the vector passed to vector->string (see section on vector->string), or in UTF-8 encoded form within a bytevector passed to utf8->string (see section on utf8->string). It is also an error for a procedure passed to string-map (see section on string-map) to return a forbidden character, or for read-string (see section on read-string) to attempt to read one.

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The text herein was sourced and adapted as described in the "R7RS attribution of various text snippets" appendix.

Categories

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• types-disjoint;

Categories recursive

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• types;