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|
{-# LANGUAGE NoImplicitPrelude #-}
{- |
Module : Text.Pandoc.BCP47
Copyright : Copyright (C) 2017–2019 John MacFarlane
License : GNU GPL, version 2 or above
Maintainer : John MacFarlane <jgm@berkeley.edu>
Stability : alpha
Portability : portable
Functions for parsing and rendering BCP47 language identifiers.
-}
module Text.Pandoc.BCP47 (
getLang
, parseBCP47
, Lang(..)
, renderLang
)
where
import Prelude
import Control.Monad (guard)
import Data.Char (isAlphaNum, isAscii, isLetter, isLower, isUpper, toLower,
toUpper)
import Data.List (intercalate)
import Text.Pandoc.Definition
import Text.Pandoc.Options
import qualified Text.Parsec as P
-- | Represents BCP 47 language/country code.
data Lang = Lang{ langLanguage :: String
, langScript :: String
, langRegion :: String
, langVariants :: [String] }
deriving (Eq, Ord, Show)
-- | Render a Lang as BCP 47.
renderLang :: Lang -> String
renderLang lang = intercalate "-" (langLanguage lang : filter (not . null)
([langScript lang, langRegion lang] ++ langVariants lang))
-- | Get the contents of the `lang` metadata field or variable.
getLang :: WriterOptions -> Meta -> Maybe String
getLang opts meta =
case lookup "lang" (writerVariables opts) of
Just s -> Just s
_ ->
case lookupMeta "lang" meta of
Just (MetaInlines [Str s]) -> Just s
Just (MetaString s) -> Just s
_ -> Nothing
-- | Parse a BCP 47 string as a Lang. Currently we parse
-- extensions and private-use fields as "variants," even
-- though officially they aren't.
parseBCP47 :: String -> Either String Lang
parseBCP47 lang =
case P.parse bcp47 "lang" lang of
Right r -> Right r
Left e -> Left $ show e
where bcp47 = do
language <- pLanguage
script <- P.option "" pScript
region <- P.option "" pRegion
variants <- P.many (pVariant P.<|> pExtension P.<|> pPrivateUse)
P.eof
return Lang{ langLanguage = language
, langScript = script
, langRegion = region
, langVariants = variants }
asciiLetter = P.satisfy (\c -> isAscii c && isLetter c)
pLanguage = do
cs <- P.many1 asciiLetter
let lcs = length cs
guard $ lcs == 2 || lcs == 3
return $ map toLower cs
pScript = P.try $ do
P.char '-'
x <- P.satisfy (\c -> isAscii c && isLetter c && isUpper c)
xs <- P.count 3
(P.satisfy (\c -> isAscii c && isLetter c && isLower c))
return $ map toLower (x:xs)
pRegion = P.try $ do
P.char '-'
cs <- P.many1 asciiLetter
let lcs = length cs
guard $ lcs == 2 || lcs == 3
return $ map toUpper cs
pVariant = P.try $ do
P.char '-'
ds <- P.option "" (P.count 1 P.digit)
cs <- P.many1 asciiLetter
let var = ds ++ cs
guard $ if null ds
then length var >= 5 && length var <= 8
else length var == 4
return $ map toLower var
pExtension = P.try $ do
P.char '-'
cs <- P.many1 $ P.satisfy (\c -> isAscii c && isAlphaNum c)
guard $ length cs >= 2 && length cs <= 8
return $ map toLower cs
pPrivateUse = P.try $ do
P.char '-'
P.char 'x'
P.char '-'
cs <- P.many1 $ P.satisfy (\c -> isAscii c && isAlphaNum c)
guard $ not (null cs) && length cs <= 8
let var = "x-" ++ cs
return $ map toLower var
|
