module GHC.Read ( Read(..) , ReadS , lex , lexLitChar , readLitChar , lexDigits , lexP , paren , parens , list , choose , readListDefault, readListPrecDefault , readParen , readp ) where import qualified Text.ParserCombinators.ReadP as P import Text.ParserCombinators.ReadP ( ReadP , ReadS , readP_to_S ) import qualified Text.Read.Lex as L import Text.ParserCombinators.ReadPrec import Data.Maybe #ifndef __HADDOCK__ import GHC.Unicode ( isDigit ) #endif import GHC.Num import GHC.Real import GHC.Float () import GHC.Show import GHC.Base import GHC.Arr import GHC.Generics (Arity(..), Associativity(..), Fixity(..))\end{code} \begin{code}
readParen :: Bool -> ReadS a -> ReadS a
readParen b g = if b then mandatory else optional
where optional r = g r ++ mandatory r
mandatory r = do
("(",s) <- lex r
(x,t) <- optional s
(")",u) <- lex t
return (x,u)
\end{code} %********************************************************* %* * \subsection{The @Read@ class} %* * %********************************************************* \begin{code}
class Read a where
readsPrec :: Int
-> ReadS a
readList :: ReadS [a]
readPrec :: ReadPrec a
readListPrec :: ReadPrec [a]
readsPrec = readPrec_to_S readPrec
readList = readPrec_to_S (list readPrec) 0
readPrec = readS_to_Prec readsPrec
readListPrec = readS_to_Prec (\_ -> readList)
readListDefault :: Read a => ReadS [a]
readListDefault = readPrec_to_S readListPrec 0
readListPrecDefault :: Read a => ReadPrec [a]
readListPrecDefault = list readPrec
lex :: ReadS String
lex s = readP_to_S L.hsLex s
lexLitChar :: ReadS String
lexLitChar = readP_to_S (do { (s, _) <- P.gather L.lexChar ;
return s })
readLitChar :: ReadS Char
readLitChar = readP_to_S L.lexChar
lexDigits :: ReadS String
lexDigits = readP_to_S (P.munch1 isDigit)
lexP :: ReadPrec L.Lexeme
lexP = lift L.lex
paren :: ReadPrec a -> ReadPrec a
paren p = do L.Punc "(" <- lexP
x <- reset p
L.Punc ")" <- lexP
return x
parens :: ReadPrec a -> ReadPrec a
parens p = optional
where
optional = p +++ mandatory
mandatory = paren optional
list :: ReadPrec a -> ReadPrec [a]
list readx =
parens
( do L.Punc "[" <- lexP
(listRest False +++ listNext)
)
where
listRest started =
do L.Punc c <- lexP
case c of
"]" -> return []
"," | started -> listNext
_ -> pfail
listNext =
do x <- reset readx
xs <- listRest True
return (x:xs)
choose :: [(String, ReadPrec a)] -> ReadPrec a
choose sps = foldr ((+++) . try_one) pfail sps
where
try_one (s,p) = do { token <- lexP ;
case token of
L.Ident s' | s==s' -> p
L.Symbol s' | s==s' -> p
_other -> pfail }
\end{code} %********************************************************* %* * \subsection{Simple instances of Read} %* * %********************************************************* \begin{code}
instance Read Char where
readPrec =
parens
( do L.Char c <- lexP
return c
)
readListPrec =
parens
( do L.String s <- lexP
return s
+++
readListPrecDefault
)
readList = readListDefault
instance Read Bool where
readPrec =
parens
( do L.Ident s <- lexP
case s of
"True" -> return True
"False" -> return False
_ -> pfail
)
readListPrec = readListPrecDefault
readList = readListDefault
instance Read Ordering where
readPrec =
parens
( do L.Ident s <- lexP
case s of
"LT" -> return LT
"EQ" -> return EQ
"GT" -> return GT
_ -> pfail
)
readListPrec = readListPrecDefault
readList = readListDefault
\end{code} %********************************************************* %* * \subsection{Structure instances of Read: Maybe, List etc} %* * %********************************************************* For structured instances of Read we start using the precedences. The idea is then that 'parens (prec k p)' will fail immediately when trying to parse it in a context with a higher precedence level than k. But if there is one parenthesis parsed, then the required precedence level drops to 0 again, and parsing inside p may succeed. 'appPrec' is just the precedence level of function application. So, if we are parsing function application, we'd better require the precedence level to be at least 'appPrec'. Otherwise, we have to put parentheses around it. 'step' is used to increase the precedence levels inside a parser, and can be used to express left- or right- associativity. For example, % is defined to be left associative, so we only increase precedence on the right hand side. Note how step is used in for example the Maybe parser to increase the precedence beyond appPrec, so that basically only literals and parenthesis-like objects such as (...) and [...] can be an argument to 'Just'. \begin{code}
instance Read a => Read (Maybe a) where
readPrec =
parens
(do L.Ident "Nothing" <- lexP
return Nothing
+++
prec appPrec (
do L.Ident "Just" <- lexP
x <- step readPrec
return (Just x))
)
readListPrec = readListPrecDefault
readList = readListDefault
instance Read a => Read [a] where
readPrec = readListPrec
readListPrec = readListPrecDefault
readList = readListDefault
instance (Ix a, Read a, Read b) => Read (Array a b) where
readPrec = parens $ prec appPrec $
do L.Ident "array" <- lexP
theBounds <- step readPrec
vals <- step readPrec
return (array theBounds vals)
readListPrec = readListPrecDefault
readList = readListDefault
instance Read L.Lexeme where
readPrec = lexP
readListPrec = readListPrecDefault
readList = readListDefault
\end{code} %********************************************************* %* * \subsection{Numeric instances of Read} %* * %********************************************************* \begin{code}
readNumber :: Num a => (L.Lexeme -> ReadPrec a) -> ReadPrec a
readNumber convert =
parens
( do x <- lexP
case x of
L.Symbol "-" -> do y <- lexP
n <- convert y
return (negate n)
_ -> convert x
)
convertInt :: Num a => L.Lexeme -> ReadPrec a
convertInt (L.Int i) = return (fromInteger i)
convertInt _ = pfail
convertFrac :: Fractional a => L.Lexeme -> ReadPrec a
convertFrac (L.Int i) = return (fromInteger i)
convertFrac (L.Rat r) = return (fromRational r)
convertFrac _ = pfail
instance Read Int where
readPrec = readNumber convertInt
readListPrec = readListPrecDefault
readList = readListDefault
instance Read Integer where
readPrec = readNumber convertInt
readListPrec = readListPrecDefault
readList = readListDefault
instance Read Float where
readPrec = readNumber convertFrac
readListPrec = readListPrecDefault
readList = readListDefault
instance Read Double where
readPrec = readNumber convertFrac
readListPrec = readListPrecDefault
readList = readListDefault
instance (Integral a, Read a) => Read (Ratio a) where
readPrec =
parens
( prec ratioPrec
( do x <- step readPrec
L.Symbol "%" <- lexP
y <- step readPrec
return (x % y)
)
)
readListPrec = readListPrecDefault
readList = readListDefault
\end{code} %********************************************************* %* * Tuple instances of Read, up to size 15 %* * %********************************************************* \begin{code}
instance Read () where
readPrec =
parens
( paren
( return ()
)
)
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b) => Read (a,b) where
readPrec = wrap_tup read_tup2
readListPrec = readListPrecDefault
readList = readListDefault
wrap_tup :: ReadPrec a -> ReadPrec a
wrap_tup p = parens (paren p)
read_comma :: ReadPrec ()
read_comma = do { L.Punc "," <- lexP; return () }
read_tup2 :: (Read a, Read b) => ReadPrec (a,b)
read_tup2 = do x <- readPrec
read_comma
y <- readPrec
return (x,y)
read_tup4 :: (Read a, Read b, Read c, Read d) => ReadPrec (a,b,c,d)
read_tup4 = do (a,b) <- read_tup2
read_comma
(c,d) <- read_tup2
return (a,b,c,d)
read_tup8 :: (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h)
=> ReadPrec (a,b,c,d,e,f,g,h)
read_tup8 = do (a,b,c,d) <- read_tup4
read_comma
(e,f,g,h) <- read_tup4
return (a,b,c,d,e,f,g,h)
instance (Read a, Read b, Read c) => Read (a, b, c) where
readPrec = wrap_tup (do { (a,b) <- read_tup2; read_comma
; c <- readPrec
; return (a,b,c) })
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d) => Read (a, b, c, d) where
readPrec = wrap_tup read_tup4
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e) => Read (a, b, c, d, e) where
readPrec = wrap_tup (do { (a,b,c,d) <- read_tup4; read_comma
; e <- readPrec
; return (a,b,c,d,e) })
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e, Read f)
=> Read (a, b, c, d, e, f) where
readPrec = wrap_tup (do { (a,b,c,d) <- read_tup4; read_comma
; (e,f) <- read_tup2
; return (a,b,c,d,e,f) })
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e, Read f, Read g)
=> Read (a, b, c, d, e, f, g) where
readPrec = wrap_tup (do { (a,b,c,d) <- read_tup4; read_comma
; (e,f) <- read_tup2; read_comma
; g <- readPrec
; return (a,b,c,d,e,f,g) })
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h)
=> Read (a, b, c, d, e, f, g, h) where
readPrec = wrap_tup read_tup8
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h,
Read i)
=> Read (a, b, c, d, e, f, g, h, i) where
readPrec = wrap_tup (do { (a,b,c,d,e,f,g,h) <- read_tup8; read_comma
; i <- readPrec
; return (a,b,c,d,e,f,g,h,i) })
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h,
Read i, Read j)
=> Read (a, b, c, d, e, f, g, h, i, j) where
readPrec = wrap_tup (do { (a,b,c,d,e,f,g,h) <- read_tup8; read_comma
; (i,j) <- read_tup2
; return (a,b,c,d,e,f,g,h,i,j) })
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h,
Read i, Read j, Read k)
=> Read (a, b, c, d, e, f, g, h, i, j, k) where
readPrec = wrap_tup (do { (a,b,c,d,e,f,g,h) <- read_tup8; read_comma
; (i,j) <- read_tup2; read_comma
; k <- readPrec
; return (a,b,c,d,e,f,g,h,i,j,k) })
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h,
Read i, Read j, Read k, Read l)
=> Read (a, b, c, d, e, f, g, h, i, j, k, l) where
readPrec = wrap_tup (do { (a,b,c,d,e,f,g,h) <- read_tup8; read_comma
; (i,j,k,l) <- read_tup4
; return (a,b,c,d,e,f,g,h,i,j,k,l) })
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h,
Read i, Read j, Read k, Read l, Read m)
=> Read (a, b, c, d, e, f, g, h, i, j, k, l, m) where
readPrec = wrap_tup (do { (a,b,c,d,e,f,g,h) <- read_tup8; read_comma
; (i,j,k,l) <- read_tup4; read_comma
; m <- readPrec
; return (a,b,c,d,e,f,g,h,i,j,k,l,m) })
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h,
Read i, Read j, Read k, Read l, Read m, Read n)
=> Read (a, b, c, d, e, f, g, h, i, j, k, l, m, n) where
readPrec = wrap_tup (do { (a,b,c,d,e,f,g,h) <- read_tup8; read_comma
; (i,j,k,l) <- read_tup4; read_comma
; (m,n) <- read_tup2
; return (a,b,c,d,e,f,g,h,i,j,k,l,m,n) })
readListPrec = readListPrecDefault
readList = readListDefault
instance (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h,
Read i, Read j, Read k, Read l, Read m, Read n, Read o)
=> Read (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) where
readPrec = wrap_tup (do { (a,b,c,d,e,f,g,h) <- read_tup8; read_comma
; (i,j,k,l) <- read_tup4; read_comma
; (m,n) <- read_tup2; read_comma
; o <- readPrec
; return (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o) })
readListPrec = readListPrecDefault
readList = readListDefault
\end{code} \begin{code}
readp :: Read a => ReadP a readp = readPrec_to_P readPrec minPrec\end{code} Instances for types of the generic deriving mechanism. \begin{code}
deriving instance Read Arity deriving instance Read Associativity deriving instance Read Fixity\end{code}
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