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module GF.Text.Lexing (stringOp) where
import Data.Char
-- lexers and unlexers - they work on space-separated word strings
stringOp :: String -> Maybe (String -> String)
stringOp name = case name of
"lextext" -> Just $ appLexer lexText
"lexcode" -> Just $ appLexer lexText
"lexmixed" -> Just $ appLexer lexMixed
"unlextext" -> Just $ appUnlexer unlexText
"unlexcode" -> Just $ appUnlexer unlexCode
"unlexmixed" -> Just $ appUnlexer unlexMixed
_ -> Nothing
appLexer :: (String -> [String]) -> String -> String
appLexer f = unwords . filter (not . null) . f
appUnlexer :: ([String] -> String) -> String -> String
appUnlexer f = f . words
lexText :: String -> [String]
lexText s = case s of
c:cs | isPunct c -> [c] : lexText cs
c:cs | isSpace c -> lexText cs
_:_ -> let (w,cs) = break (\x -> isSpace x || isPunct x) s in w : lexText cs
_ -> [s]
-- | Haskell lexer, usable for much code
lexCode :: String -> [String]
lexCode ss = case lex ss of
[(w@(_:_),ws)] -> w : lexCode ws
_ -> []
-- | LaTeX style lexer, with "math" environment using Code between $...$
lexMixed :: String -> [String]
lexMixed = concat . alternate False where
alternate env s = case s of
_:_ -> case break (=='$') s of
(t,[]) -> lex env t : []
(t,c:m) -> lex env t : [[c]] : alternate (not env) m
_ -> []
lex env = if env then lexCode else lexText
unlexText :: [String] -> String
unlexText s = case s of
w:[] -> w
w:[c]:[] | isPunct c -> w ++ [c]
w:[c]:cs | isPunct c -> w ++ [c] ++ " " ++ unlexText cs
w:ws -> w ++ " " ++ unlexText ws
_ -> []
unlexCode :: [String] -> String
unlexCode s = case s of
w:[] -> w
[c]:cs | isParen c -> [c] ++ unlexCode cs
w:cs@([c]:_) | isClosing c -> w ++ unlexCode cs
w:ws -> w ++ " " ++ unlexCode ws
_ -> []
unlexMixed :: [String] -> String
unlexMixed = concat . alternate False where
alternate env s = case s of
_:_ -> case break (=="$") s of
(t,[]) -> unlex env t : []
(t,c:m) -> unlex env t : sep env c : alternate (not env) m
_ -> []
unlex env = if env then unlexCode else unlexText
sep env c = if env then c ++ " " else " " ++ c
isPunct = flip elem ".?!,:;"
isParen = flip elem "()[]{}"
isClosing = flip elem ")]}"
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