BCP-47 compliant language tag predicates🔗ℹ

package: langtag

This module provides a single predicate that determines whether a given string is a valid Language Tag as defined by RFC5646 and used across HTTP, HTML, XML, RDF, and much more.

References

BCP-47, RFC5646 Tags for Identifying Languages
IANA Registry of Language Tags (Assigned)
IANA Registry of Language Subtags
IANA Registry of Language Tag Extensions (UCD)

predicate
(language-tag? val) → boolean?
val : (or/c symbol? string?)

Returns #t if the string val is a valid BCP-47 language tag.

Examples:

> (require langtag)
> (language-tag? "en")
#t
> (language-tag? "en-US")
#t
> (language-tag? "en-US-boont")
#t
> (language-tag? "en-Latn-US")
#t
> (language-tag? "i-klingon")
#t
> (language-tag? "x-private")
#t

1 Components🔗ℹ

predicate
(normal-use? val) → boolean?
  val : (or/c symbol? string?)
predicate
(private-use? val) → boolean?
  val : (or/c symbol? string?)
predicate
(grandfathered? val) → boolean?
  val : (or/c symbol? string?)

Returns #t if the string val corresponds to one of the three top-level productions for the rule Language-Tag.

Examples:

> (require langtag)
> (for-each (lambda (val) (displayln (format "~s ~s ~s"
                                             (normal-use? val)
                                             (private-use? val)
                                             (grandfathered? val))))
            '("en-US" "x-private" "i-klingon"))
#t #f #f
#f #t #f
#f #f #t

predicate
(language-part? val) → boolean?
  val : (or/c symbol? string?)
predicate
(language-script-part? val) → boolean?
  val : (or/c symbol? string?)
predicate
(language-region-part? val) → boolean?
  val : (or/c symbol? string?)
predicate
(language-variant-part? val) → boolean?
  val : (or/c symbol? string?)
predicate
(language-extension-part? val) → boolean?
  val : (or/c symbol? string?)
predicate
(language-private-use-part? val) → boolean?
  val : (or/c symbol? string?)

Returns #t if the string val corresponds to one of the components of a normal-use language tag.

2 Matching🔗ℹ

procedure
(language-tag-match val)
→ (list symbol? string? (or/c (listof (cons/c symbol? string?)) none/c))
val : (or/c symbol? string?)

TBD

Examples:

> (require langtag)
> (language-tag-match "en")
'(lang "en" ((language . "en")))
> (language-tag-match "en-US")
'(lang "en-US" ((language . "en") (region . "US")))
> (language-tag-match "en-US-boont")
'(lang "en-US-boont" ((language . "en") (region . "US") (variant . "boont")))
> (language-tag-match "en-Latn-US")
'(lang "en-Latn-US" ((language . "en") (script . "Latn") (region . "US")))
> (language-tag-match "i-klingon")
'(grandfathered-i "i-klingon")
> (language-tag-match "x-private")
'(private-use "x-private")

3 Appendix: Definition🔗ℹ

The syntax of the language tag, from [RFC5646], in ABNF [RFC5234] is:

Language-Tag = langtag ; normal language tags

/ privateuse ; private use tag

/ grandfathered ; grandfathered tags

langtag = language

["-" script]

["-" region]

*("-" variant)

*("-" extension)

["-" privateuse]

language = 2*3ALPHA ; shortest ISO 639 code

["-" extlang] ; sometimes followed by

; extended language subtags

/ 4ALPHA ; or reserved for future use

/ 5*8ALPHA ; or registered language subtag

extlang = 3ALPHA ; selected ISO 639 codes

*2("-" 3ALPHA) ; permanently reserved

script = 4ALPHA ; ISO 15924 code

region = 2ALPHA ; ISO 3166-1 code

/ 3DIGIT ; UN M.49 code

variant = 5*8alphanum ; registered variants

/ (DIGIT 3alphanum)

extension = singleton 1*("-" (2*8alphanum))

; Single alphanumerics

; "x" reserved for private use

singleton = DIGIT ; 0 - 9

/ %x41-57 ; A - W

/ %x59-5A ; Y - Z

/ %x61-77 ; a - w

/ %x79-7A ; y - z

privateuse = "x" 1*("-" (1*8alphanum))

grandfathered = irregular ; non-redundant tags registered

/ regular ; during the RFC 3066 era

irregular = "en-GB-oed" ; irregular tags do not match

/ "i-ami" ; the 'langtag' production and

/ "i-bnn" ; would not otherwise be

/ "i-default" ; considered 'well-formed'

/ "i-enochian" ; These tags are all valid,

/ "i-hak" ; but most are deprecated

/ "i-klingon" ; in favor of more modern

/ "i-lux" ; subtags or subtag

/ "i-mingo" ; combination

/ "i-navajo"

/ "i-pwn"

/ "i-tao"

/ "i-tay"

/ "i-tsu"

/ "sgn-BE-FR"

/ "sgn-BE-NL"

/ "sgn-CH-DE"

regular = "art-lojban" ; these tags match the 'langtag'

/ "cel-gaulish" ; production, but their subtags

/ "no-bok" ; are not extended language

/ "no-nyn" ; or variant subtags: their meaning

/ "zh-guoyu" ; is defined by their registration

/ "zh-hakka" ; and all of these are deprecated

/ "zh-min" ; in favor of a more modern

/ "zh-min-nan" ; subtag or sequence of subtags

/ "zh-xiang"

alphanum = (ALPHA / DIGIT) ; letters and numbers