X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FRead.lhs;h=77daececb7306dfda10659d977d823f7114a3d82;hb=be2750a0a11b919fb03cc070074e430f88bdfa90;hp=68167e27b69cf23dc2f85dd17a7cdd4b84875924;hpb=0221746dbe04e384750145c94afd27c3c0be4d59;p=ghc-base.git diff --git a/GHC/Read.lhs b/GHC/Read.lhs index 68167e2..77daece 100644 --- a/GHC/Read.lhs +++ b/GHC/Read.lhs @@ -1,5 +1,7 @@ \begin{code} -{-# OPTIONS_GHC -fno-implicit-prelude #-} +{-# LANGUAGE CPP, NoImplicitPrelude #-} +{-# OPTIONS_HADDOCK hide #-} + ----------------------------------------------------------------------------- -- | -- Module : GHC.Read @@ -15,24 +17,18 @@ ----------------------------------------------------------------------------- -- #hide -module GHC.Read +module GHC.Read ( Read(..) -- class - + -- ReadS type , ReadS -- :: *; = String -> [(a,String)] - - -- utility functions - , reads -- :: Read a => ReadS a - , readp -- :: Read a => ReadP a - , readEither -- :: Read a => String -> Either String a - , read -- :: Read a => String -> a -- H98 compatibility - , lex -- :: ReadS String - , lexLitChar -- :: ReadS String - , readLitChar -- :: ReadS Char - , lexDigits -- :: ReadS String - + , lex -- :: ReadS String + , lexLitChar -- :: ReadS String + , readLitChar -- :: ReadS Char + , lexDigits -- :: ReadS String + -- defining readers , lexP -- :: ReadPrec Lexeme , paren -- :: ReadPrec a -> ReadPrec a @@ -43,6 +39,9 @@ module GHC.Read -- Temporary , readParen + + -- XXX Can this be removed? + , readp ) where @@ -63,15 +62,13 @@ import qualified Text.Read.Lex as L import Text.ParserCombinators.ReadPrec import Data.Maybe -import Data.Either -import {-# SOURCE #-} GHC.Err ( error ) #ifndef __HADDOCK__ -import {-# SOURCE #-} GHC.Unicode ( isDigit ) +import {-# SOURCE #-} GHC.Unicode ( isDigit ) #endif import GHC.Num import GHC.Real -import GHC.Float +import GHC.Float () import GHC.Show import GHC.Base import GHC.Arr @@ -89,17 +86,17 @@ 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) + ("(",s) <- lex r + (x,t) <- optional s + (")",u) <- lex t + return (x,u) \end{code} %********************************************************* -%* * +%* * \subsection{The @Read@ class} -%* * +%* * %********************************************************* \begin{code} @@ -133,25 +130,45 @@ readParen b g = if b then mandatory else optional -- > infixr 5 :^: -- > data Tree a = Leaf a | Tree a :^: Tree a -- --- the derived instance of 'Read' is equivalent to +-- the derived instance of 'Read' in Haskell 98 is equivalent to -- -- > instance (Read a) => Read (Tree a) where -- > --- > readsPrec d r = readParen (d > up_prec) +-- > readsPrec d r = readParen (d > app_prec) +-- > (\r -> [(Leaf m,t) | +-- > ("Leaf",s) <- lex r, +-- > (m,t) <- readsPrec (app_prec+1) s]) r +-- > +-- > ++ readParen (d > up_prec) -- > (\r -> [(u:^:v,w) | -- > (u,s) <- readsPrec (up_prec+1) r, -- > (":^:",t) <- lex s, -- > (v,w) <- readsPrec (up_prec+1) t]) r -- > --- > ++ readParen (d > app_prec) --- > (\r -> [(Leaf m,t) | --- > ("Leaf",s) <- lex r, --- > (m,t) <- readsPrec (app_prec+1) s]) r --- > --- > where up_prec = 5 --- > app_prec = 10 +-- > where app_prec = 10 +-- > up_prec = 5 -- -- Note that right-associativity of @:^:@ is unused. +-- +-- The derived instance in GHC is equivalent to +-- +-- > instance (Read a) => Read (Tree a) where +-- > +-- > readPrec = parens $ (prec app_prec $ do +-- > Ident "Leaf" <- lexP +-- > m <- step readPrec +-- > return (Leaf m)) +-- > +-- > +++ (prec up_prec $ do +-- > u <- step readPrec +-- > Symbol ":^:" <- lexP +-- > v <- step readPrec +-- > return (u :^: v)) +-- > +-- > where app_prec = 10 +-- > up_prec = 5 +-- > +-- > readListPrec = readListPrecDefault class Read a where -- | attempts to parse a value from the front of the string, returning @@ -167,10 +184,10 @@ class Read a where -- 'Text.Show.showsPrec', and delivers the value that -- 'Text.Show.showsPrec' started with. - readsPrec :: Int -- ^ the operator precedence of the enclosing - -- context (a number from @0@ to @11@). - -- Function application has precedence @10@. - -> ReadS a + readsPrec :: Int -- ^ the operator precedence of the enclosing + -- context (a number from @0@ to @11@). + -- Function application has precedence @10@. + -> ReadS a -- | The method 'readList' is provided to allow the programmer to -- give a specialised way of parsing lists of values. @@ -183,6 +200,8 @@ class Read a where readPrec :: ReadPrec a -- | Proposed replacement for 'readList' using new-style parsers (GHC only). + -- The default definition uses 'readList'. Instances that define 'readPrec' + -- should also define 'readListPrec' as 'readListPrecDefault'. readListPrec :: ReadPrec [a] -- default definitions @@ -192,43 +211,17 @@ class Read a where readListPrec = readS_to_Prec (\_ -> readList) readListDefault :: Read a => ReadS [a] --- ^ Use this to define the 'readList' method, if you don't want a special --- case (GHC only; for other systems the default suffices). +-- ^ A possible replacement definition for the 'readList' method (GHC only). +-- This is only needed for GHC, and even then only for 'Read' instances +-- where 'readListPrec' isn't defined as 'readListPrecDefault'. readListDefault = readPrec_to_S readListPrec 0 readListPrecDefault :: Read a => ReadPrec [a] --- ^ Use this to define the 'readListPrec' method, if you --- don't want a special case (GHC only). +-- ^ A possible replacement definition for the 'readListPrec' method, +-- defined using 'readPrec' (GHC only). readListPrecDefault = list readPrec ------------------------------------------------------------------------ --- utility functions - --- | equivalent to 'readsPrec' with a precedence of 0. -reads :: Read a => ReadS a -reads = readsPrec minPrec - -readp :: Read a => ReadP a -readp = readPrec_to_P readPrec minPrec - -readEither :: Read a => String -> Either String a -readEither s = - case [ x | (x,"") <- readPrec_to_S read' minPrec s ] of - [x] -> Right x - [] -> Left "Prelude.read: no parse" - _ -> Left "Prelude.read: ambiguous parse" - where - read' = - do x <- readPrec - lift P.skipSpaces - return x - --- | The 'read' function reads input from a string, which must be --- completely consumed by the input process. -read :: Read a => String -> a -read s = either error id (readEither s) - ------------------------------------------------------------------------- -- H98 compatibility -- | The 'lex' function reads a single lexeme from the input, discarding @@ -246,7 +239,7 @@ read s = either error id (readEither s) -- * Octal and hexadecimal numerics are not recognized as a single token -- -- * Comments are not treated properly -lex :: ReadS String -- As defined by H98 +lex :: ReadS String -- As defined by H98 lex s = readP_to_S L.hsLex s -- | Read a string representation of a character, using Haskell @@ -254,11 +247,11 @@ lex s = readP_to_S L.hsLex s -- -- > lexLitChar "\\nHello" = [("\\n", "Hello")] -- -lexLitChar :: ReadS String -- As defined by H98 +lexLitChar :: ReadS String -- As defined by H98 lexLitChar = readP_to_S (do { (s, _) <- P.gather L.lexChar ; - return s }) - -- There was a skipSpaces before the P.gather L.lexChar, - -- but that seems inconsistent with readLitChar + return s }) + -- There was a skipSpaces before the P.gather L.lexChar, + -- but that seems inconsistent with readLitChar -- | Read a string representation of a character, using Haskell -- source-language escape conventions, and convert it to the character @@ -266,7 +259,7 @@ lexLitChar = readP_to_S (do { (s, _) <- P.gather L.lexChar ; -- -- > readLitChar "\\nHello" = [('\n', "Hello")] -- -readLitChar :: ReadS Char -- As defined by H98 +readLitChar :: ReadS Char -- As defined by H98 readLitChar = readP_to_S L.lexChar -- | Reads a non-empty string of decimal digits. @@ -282,16 +275,16 @@ lexP = lift L.lex paren :: ReadPrec a -> ReadPrec a -- ^ @(paren p)@ parses \"(P0)\" --- where @p@ parses \"P0\" in precedence context zero +-- where @p@ parses \"P0\" in precedence context zero paren p = do L.Punc "(" <- lexP - x <- reset p - L.Punc ")" <- lexP - return x + x <- reset p + L.Punc ")" <- lexP + return x parens :: ReadPrec a -> ReadPrec a -- ^ @(parens p)@ parses \"P\", \"(P0)\", \"((P0))\", etc, --- where @p@ parses \"P\" in the current precedence context --- parses \"P0\" in precedence context zero +-- where @p@ parses \"P\" in the current precedence context +-- and parses \"P0\" in precedence context zero parens p = optional where optional = p +++ mandatory @@ -322,17 +315,22 @@ choose :: [(String, ReadPrec a)] -> ReadPrec a -- ^ Parse the specified lexeme and continue as specified. -- Esp useful for nullary constructors; e.g. -- @choose [(\"A\", return A), (\"B\", return B)]@ +-- We match both Ident and Symbol because the constructor +-- might be an operator eg (:=:) choose sps = foldr ((+++) . try_one) pfail sps - where - try_one (s,p) = do { L.Ident s' <- lexP ; - if s == s' then p else pfail } + 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} @@ -345,11 +343,11 @@ instance Read Char where readListPrec = parens - ( do L.String s <- lexP -- Looks for "foo" + ( do L.String s <- lexP -- Looks for "foo" return s +++ - readListPrecDefault -- Looks for ['f','o','o'] - ) -- (more generous than H98 spec) + readListPrecDefault -- Looks for ['f','o','o'] + ) -- (more generous than H98 spec) readList = readListDefault @@ -383,9 +381,9 @@ instance Read Ordering where %********************************************************* -%* * +%* * \subsection{Structure instances of Read: Maybe, List etc} -%* * +%* * %********************************************************* For structured instances of Read we start using the precedences. The @@ -417,7 +415,7 @@ instance Read a => Read (Maybe a) where return Nothing +++ prec appPrec ( - do L.Ident "Just" <- lexP + do L.Ident "Just" <- lexP x <- step readPrec return (Just x)) ) @@ -425,23 +423,6 @@ instance Read a => Read (Maybe a) where readListPrec = readListPrecDefault readList = readListDefault -instance (Read a, Read b) => Read (Either a b) where - readPrec = - parens - ( prec appPrec - ( do L.Ident "Left" <- lexP - x <- step readPrec - return (Left x) - +++ - do L.Ident "Right" <- lexP - y <- step readPrec - return (Right y) - ) - ) - - readListPrec = readListPrecDefault - readList = readListDefault - instance Read a => Read [a] where readPrec = readListPrec readListPrec = readListPrecDefault @@ -449,10 +430,10 @@ instance Read a => Read [a] where instance (Ix a, Read a, Read b) => Read (Array a b) where readPrec = parens $ prec appPrec $ - do L.Ident "array" <- lexP - bounds <- step readPrec - vals <- step readPrec - return (array bounds vals) + do L.Ident "array" <- lexP + theBounds <- step readPrec + vals <- step readPrec + return (array theBounds vals) readListPrec = readListPrecDefault readList = readListDefault @@ -465,34 +446,34 @@ instance Read L.Lexeme where %********************************************************* -%* * +%* * \subsection{Numeric instances of Read} -%* * +%* * %********************************************************* \begin{code} -readNumber :: Num a => (L.Lexeme -> Maybe a) -> ReadPrec a +readNumber :: Num a => (L.Lexeme -> ReadPrec a) -> ReadPrec a -- Read a signed number readNumber convert = parens ( do x <- lexP case x of - L.Symbol "-" -> do n <- readNumber convert + L.Symbol "-" -> do y <- lexP + n <- convert y return (negate n) - - _ -> case convert x of - Just n -> return n - Nothing -> pfail + + _ -> convert x ) -convertInt :: Num a => L.Lexeme -> Maybe a -convertInt (L.Int i) = Just (fromInteger i) -convertInt _ = Nothing -convertFrac :: Fractional a => L.Lexeme -> Maybe a -convertFrac (L.Int i) = Just (fromInteger i) -convertFrac (L.Rat r) = Just (fromRational r) -convertFrac _ = Nothing +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 @@ -531,9 +512,9 @@ instance (Integral a, Read a) => Read (Ratio a) where %********************************************************* -%* * - Tuple instances of Read, up to size 15 -%* * +%* * + Tuple instances of Read, up to size 15 +%* * %********************************************************* \begin{code} @@ -562,29 +543,29 @@ read_comma = do { L.Punc "," <- lexP; return () } read_tup2 :: (Read a, Read b) => ReadPrec (a,b) -- Reads "a , b" no parens! read_tup2 = do x <- readPrec - read_comma - y <- readPrec - return (x,y) + 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_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) + => 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) }) + ; c <- readPrec + ; return (a,b,c) }) readListPrec = readListPrecDefault readList = readListDefault @@ -595,99 +576,107 @@ instance (Read a, Read b, Read c, Read d) => Read (a, b, c, d) where 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) }) + ; 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 + => 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) }) + ; (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 + => 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) }) + ; (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 + => 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 + 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) }) + ; 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 + 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) }) + ; (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 + 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) }) + ; (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 + 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) }) + ; (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 + 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) }) + ; (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 + 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) }) + ; (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 + 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) }) + ; (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} +-- XXX Can this be removed? + +readp :: Read a => ReadP a +readp = readPrec_to_P readPrec minPrec +\end{code} +