2 Character Sets

2 Character Sets🔗ℹ

This section documents the character-set utilities used by string-count and available directly through string-tools/char-set.

Conceptually, a character set represents a collection of characters with membership operations and set operations such as union, intersection, and difference. It is useful when you want to classify characters efficiently and reuse that classification across multiple string-processing steps.

Character sets are represented with a hybrid structure: an ASCII bit mask for codepoints 0 through 127, plus a normalized collection of non-ASCII inclusive ranges. This representation gives fast membership tests for common ASCII text while keeping non-ASCII sets compact.

(require string-tools/char-set)

package: string-tools-lib

procedure
(char-set? v) → boolean?
v : any/c

Returns #t when v is a character set value.

Examples:

> (require string-tools/char-set)
> (char-set? (make-char-set #\a #\b))
#t
> (char-set? "ab")
#f

value
empty-char-set : char-set?

The empty character set.

Examples:

> (require string-tools/char-set)
> (char-set-size empty-char-set)
0
> (char-set-member? empty-char-set #\a)
#f

procedure
(make-char-set ch ...) → char-set?
ch : char?

Builds a character set containing the given characters.

Examples:

> (require string-tools/char-set)
> (make-char-set #\a #\b #\a)
(char-set 475368975085586025561263702016 '#())

procedure
(list->char-set xs) → char-set?
xs : (listof char?)

Builds a character set from a list of characters.

Examples:

> (require string-tools/char-set)
> (define cs (list->char-set (list #\a #\b #\a)))
> (char-set-size cs)
2
> (char-set-member? cs #\b)
#t

procedure
(string->char-set s) → char-set?
s : string?

Builds a character set from the distinct characters in s.

Examples:

> (require string-tools/char-set)
> (define cs (string->char-set "banana"))
> (char-set-size cs)
3
> (char-set-member? cs #\n)
#t

procedure
(char-set-add cs ch) → char-set?
cs : char-set?
ch : char?

Returns a character set containing all characters in cs and ch.

Examples:

> (require string-tools/char-set)
> (define cs (char-set-add empty-char-set #\x))
> (char-set-member? cs #\x)
#t

procedure
(char-set-add-range cs lo-ch hi-ch) → char-set?
  cs : char-set?
  lo-ch : char?
  hi-ch : char?

Returns a character set containing cs plus all characters from lo-ch to hi-ch, inclusive.

Examples:

> (require string-tools/char-set)
> (define letters (char-set-add-range empty-char-set #\a #\z))
> (char-set-member? letters #\m)
#t
> (char-set-member? letters #\A)
#f

procedure
(char-set-member? cs ch) → boolean?
cs : char-set?
ch : char?

Checks whether ch is in cs.

Examples:

> (require string-tools/char-set)
> (define vowels (make-char-set #\a #\e #\i #\o #\u))
> (char-set-member? vowels #\e)
#t
> (char-set-member? vowels #\y)
#f

procedure
(char-set-union a b) → char-set?
a : char-set?
b : char-set?

Returns the union of a and b.

Examples:

> (require string-tools/char-set)
> (define vowels (make-char-set #\a #\e #\i #\o #\u))
> (define y (make-char-set #\y))
> (char-set-member? (char-set-union vowels y) #\y)
#t

procedure
(char-set-intersection a b) → char-set?
a : char-set?
b : char-set?

Returns the intersection of a and b.

Examples:

> (require string-tools/char-set)
> (define a (make-char-set #\a #\b #\c))
> (define b (make-char-set #\b #\c #\d))
> (char-set-size (char-set-intersection a b))
2

procedure
(char-set-difference a b) → char-set?
a : char-set?
b : char-set?

Returns the set difference a - b.

Examples:

> (require string-tools/char-set)
> (define letters (char-set-add-range empty-char-set #\a #\f))
> (define vowels (make-char-set #\a #\e))
> (char-set-member? (char-set-difference letters vowels) #\b)
#t
> (char-set-member? (char-set-difference letters vowels) #\a)
#f

procedure
(char-set-size cs) → exact-nonnegative-integer?
cs : char-set?

Returns the number of characters in cs.

Examples:

> (require string-tools/char-set)
> (char-set-size (make-char-set #\a #\b #\a))
2

Examples:

> (require string-tools/char-set)
> (define vowels (make-char-set #\a #\e #\i #\o #\u))
> (char-set-member? vowels #\e)
#t
> (char-set-size vowels)
5
> (define letters (char-set-add-range empty-char-set #\a #\z))
> (char-set-size (char-set-difference letters vowels))
21