ref: ea2a7891b8b9c91747d343f5c42de8dbbd8b1c76
dir: /lib/Text/Read/Lex.hs/
module Text.Read.Lex(lex, dropSpace) where
import Primitives
import Data.Bool
import Data.Char
import Data.Eq
import Data.List
import Data.Ord
type ReadS a = String -> [(a, String)]
lex :: ReadS String
lex [] = [("","")]
lex ('\'':s) = [('\'':ch++"'", t) | (ch,'\'':t) <- lexLitChar s,
ch /= "'" ]
lex ('"':s) = [('"':str, t) | (str,t) <- lexString s]
where
lexString ('"':s) = [("\"",s)]
lexString s = [(ch++str, u)
| (ch,t) <- lexStrItem s,
(str,u) <- lexString t ]
lexStrItem ('\\':'&':s) = [("\\&",s)]
lexStrItem ('\\':c:s) | isSpace c = [("\\&",t) |
'\\':t <- [dropSpace s]]
lexStrItem s = lexLitChar s
lex (c:s) | isSpace c = lex s
| isSingle c = [([c],s)]
| isSym c = [(c:sym,t) | (sym,t) <- [span isSym s]]
| isAlpha c = [(c:nam,t) | (nam,t) <- [span isIdChar s]]
| isDigit c = [(c:ds++fe,t) | (ds,s) <- [span isDigit s],
(fe,t) <- lexFracExp s ]
| otherwise = [] -- bad character
where
isSingle c = c `elem` ",;()[]{}_`"
isSym c = c `elem` "!@#$%&?+./<=>?\\^|:-~"
isIdChar c = isAlphaNum c || c `elem` "_'"
lexFracExp ('.':c:cs) | isDigit c
= [('.':ds++e,u) | (ds,t) <- lexDigits (c:cs),
(e,u) <- lexExp t]
lexFracExp s = lexExp s
lexExp (e:s) | e `elem` "eE"
= [(e:c:ds,u) | (c:t) <- [s], c `elem` "+-",
(ds,u) <- lexDigits t] ++
[(e:ds,t) | (ds,t) <- lexDigits s]
lexExp s = [("",s)]
lexDigits :: ReadS String
lexDigits s = [(cs, t) | (cs@(_:_), t) <- [span isDigit s]]
lexLitChar :: ReadS String
lexLitChar ('\\':s) = [ prefix '\\' c | c <- lexEsc s ]
where
lexEsc (c:s) | c `elem` "abfnrtv\\\"'" = [([c],s)]
lexEsc ('^':c:s) | c >= '@' && c <= '_' = [(['^',c],s)]
lexEsc ('o':s) = [prefix 'o' (span isOctDigit s)]
lexEsc ('x':s) = [prefix 'x' (span isHexDigit s)]
lexEsc s@(d:_) | isDigit d = [span isDigit s]
lexEsc _ = []
prefix c (t,s) = (c:t, s)
lexLitChar (c:cs) = [([c], cs)]
lexLitChar [] = []
dropSpace :: String -> String
dropSpace [] = []
dropSpace ccs@(c:cs) | isSpace c = dropSpace cs
| True = ccs