ref: a16c884ed8631365a4e96e5c552120e5fc748435
dir: /lib/Text/Read.hs/
module Text.Read(
ReadS,
Read(..),
read,
readMaybe,
readParen,
) where
import Primitives
import Control.Error
import Control.Monad
import Data.Char
import Data.Bool_Type
import Data.Eq
import Data.List_Type
import Data.Maybe_Type
type String = [Char]
type ReadS a = String -> [(a, String)]
class Read a where
readsPrec :: Int -> ReadS a
readList :: ReadS [a]
read :: forall a . Read a => String -> a
read s =
case readsPrec 0 s of
[(a, [])] -> a
_ -> error "read: failed"
readMaybe :: forall a . Read a => String -> Maybe a
readMaybe s =
case readsPrec 0 s of
[(a, [])] -> Just a
_ -> Nothing
readParen :: forall a . Bool -> ReadS a -> ReadS a
readParen b g =
if b then mandatory else optional
where
optional :: ReadS a
optional r = g r ++ mandatory r
mandatory :: ReadS a
mandatory r = do
-- XXX compiler broken ('(',s) <- lex r
(lp,s) <- lex r
guard (lp == '(')
(x,t) <- optional s
-- (')',u) <- lex t
(rp,u) <- lex t
guard (rp == ')')
return (x,u)
-- Really bad lexer
lex :: ReadS Char
lex "" = []
lex (c:cs) | isSpace c = lex cs
| True = [(c, cs)]