diff --git a/Data/Accessor.hs b/Data/Accessor.hs deleted file mode 100644 --- a/Data/Accessor.hs +++ /dev/null @@ -1,145 +0,0 @@ -{-# LANGUAGE TemplateHaskell, CPP #-} - --- |This module provides a simple abstract data type for --- a piece of a data stucture that can be read from and --- written to. It provides an automatic Template Haskell --- routine to scour data type definitions and generate --- accessor objects for them automatically. - -module Data.Accessor - ( Accessor(..) - , nameDeriveAccessors, deriveAccessors - , getA, putA, modA - , (.>), (<.), (=:) - ) -where - -import Language.Haskell.TH -import Language.Haskell.TH.Syntax -import Data.Maybe (catMaybes) -import Control.Monad (guard) -import Control.Monad.State - --- |An @Accessor s a@ is an object that encodes how to --- get and put a subject of type @a@ out of/into an object --- of type @s@. --- --- In order for an instance of this data structure @a@ to be --- an "Accessor", it must obey the following laws: --- --- > getVal a (setVal a x s) = x --- > setVal a (getVal a s) s = s -data Accessor s a - = Accessor { getVal :: s -> a - , setVal :: a -> s -> s - } - -infixl 9 .> --- |Accessor composition. -(.>) :: Accessor a b -> Accessor b c -> Accessor a c -f .> g = - Accessor { getVal = getVal g . getVal f - , setVal = \c a -> setVal f (setVal g c (getVal f a)) a - } - -infixr 9 <. --- |Accessor composition the other direction. --- --- > (<.) = flip (.>) -(<.) :: Accessor b c -> Accessor a b -> Accessor a c -(<.) = flip (.>) - -infix 1 =: --- |An "assignment operator" for state monads. --- --- > (=:) = putA -(=:) :: MonadState s m => Accessor s a -> a -> m () -(=:) = putA - --- |A structural dereference function for state monads. -getA :: MonadState s m => Accessor s a -> m a -getA a = liftM (getVal a) get - --- |A structural assignment function for state monads. -putA :: MonadState s m => Accessor s a -> a -> m () -putA a x = get >>= put . setVal a x - --- |A structural modification function for state monads. -modA :: MonadState s m => Accessor s a -> (a -> a) -> m () -modA a f = liftM f (getA a) >>= putA a - --- |@deriveAccessors n@ where @n@ is the name of a data type --- declared with @data@ looks through all the declared fields --- of the data type, and for each field ending in an underscore --- generates an accessor of the same name without the underscore. --- --- It is "nameDeriveAccessors" n f where @f@ satisfies --- --- > f (s ++ "_") = Just s --- > f x = x -- otherwise --- --- For example, given the data type: --- --- > data Score = Score { p1Score_ :: Int --- > , p2Score_ :: Int --- > , rounds :: Int --- > } --- --- @deriveAccessors@ will generate the following objects: --- --- > p1Score :: Accessor Score Int --- > p1Score = Accessor p1Score_ (\x s -> s { p1Score_ = x }) --- > p2Score :: Accessor Score Int --- > p2Score = Accessor p2Score_ (\x s -> s { p2Score_ = x }) --- -deriveAccessors :: Name -> Q [Dec] -deriveAccessors n = nameDeriveAccessors n transformName - where - transformName s = do - guard $ not (null s) - guard $ last s == '_' - return $ init s - --- |@nameDeriveAccessors n f@ where @n@ is the name of a data type --- declared with @data@ and @f@ is a function from names of fields --- in that data type to the name of the corresponding accessor. If --- @f@ returns @Nothing@, then no accessor is generated for that --- field. -nameDeriveAccessors :: Name -> (String -> Maybe String) -> Q [Dec] -nameDeriveAccessors t namer = do - TyConI (DataD _ name _ cons _) <- reify t - liftM concat $ mapM makeAccs cons - - where - - makeAccs :: Con -> Q [Dec] - makeAccs (RecC _ vars) = - liftM catMaybes $ mapM (\ (name,_,_) -> makeAccFromName name) vars - makeAccs (ForallC _ _ c) = makeAccs c - makeAccs _ = return [] - - transformName :: Name -> Maybe Name - transformName (Name occ f) = do - n <- namer (occString occ) - return $ Name (mkOccName n) f - - makeAccFromName :: Name -> Q (Maybe Dec) - makeAccFromName name = do - case transformName name of - Nothing -> return Nothing - Just n -> liftM Just $ makeAcc name n - - -- haddock doesn't grok TH -#ifndef __HADDOCK__ - - makeAcc :: Name -> Name -> Q Dec - makeAcc name accName = do - body <- [| - Accessor { getVal = $( return $ VarE name ) - , setVal = \x s -> - $( return $ RecUpdE (VarE 's) [(name, VarE 'x)] ) - } - |] - return $ ValD (VarP accName) (NormalB body) [] - -#endif diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/LICENSE @@ -0,0 +1,674 @@ + GNU GENERAL PUBLIC LICENSE + Version 3, 29 June 2007 + + Copyright (C) 2007 Free Software Foundation, Inc. + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + Preamble + + The GNU General Public License is a free, copyleft license for +software and other kinds of works. + + The licenses for most software and other practical works are designed +to take away your freedom to share and change the works. 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If not, see . + +Also add information on how to contact you by electronic and paper mail. + + If the program does terminal interaction, make it output a short +notice like this when it starts in an interactive mode: + + Copyright (C) + This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. + This is free software, and you are welcome to redistribute it + under certain conditions; type `show c' for details. + +The hypothetical commands `show w' and `show c' should show the appropriate +parts of the General Public License. Of course, your program's commands +might be different; for a GUI interface, you would use an "about box". + + You should also get your employer (if you work as a programmer) or school, +if any, to sign a "copyright disclaimer" for the program, if necessary. +For more information on this, and how to apply and follow the GNU GPL, see +. + + The GNU General Public License does not permit incorporating your program +into proprietary programs. If your program is a subroutine library, you +may consider it more useful to permit linking proprietary applications with +the library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. But first, please read +. diff --git a/Setup.lhs b/Setup.lhs --- a/Setup.lhs +++ b/Setup.lhs @@ -1,4 +1,3 @@ #! /usr/bin/env runhaskell - > import Distribution.Simple > main = defaultMain diff --git a/data-accessor.cabal b/data-accessor.cabal --- a/data-accessor.cabal +++ b/data-accessor.cabal @@ -1,18 +1,64 @@ -Name: data-accessor +Name: data-accessor +Version: 0.1.1 +License: GPL +License-File: LICENSE +Author: Henning Thielemann , Luke Palmer +Maintainer: Henning Thielemann +Homepage: http://code.haskell.org/data-accessor/ +Category: Data +-- Portability: Haskell98, not quite because of MTL dependency +Build-Type: Simple +Build-Depends: base>=1.0, mtl +Synopsis: Utilities for accessing and manipulating fields of records Description: - This module provides a simple abstract data type for - a piece of a data stucture that can be read from and - written to. It provides an automatic Template Haskell - routine to scour data type definitions and generate - accessor objects for them automatically. -Version: 0.0.1 -Stability: experimental -Synopsis: Automatically generate composable accessors for data types. -License: LGPL -Category: Data -Author: Luke Palmer -Maintainer: lrpalmer@gmail.com -Build-Type: Simple -Build-Depends: base, template-haskell, mtl -Exposed-Modules: Data.Accessor -Extensions: CPP, TemplateHaskell + In Haskell 98 the name of a record field + is automatically also the name of a function which gets the value + of the according field. + E.g. if we have + . + data Pair a b = Pair {first :: a, second :: b} + . + then + . + > first :: Pair a b -> a + > second :: Pair a b -> b + . + However for setting or modifying a field value + we need to use some syntactic sugar, which is often clumsy. + . + modifyFirst :: (a -> a) -> (Pair a b -> Pair a b) + modifyFirst f r\@(Pair {first=a}) = r{first = f a} + . + With this package you can define record field accessors + which allow setting, getting and modifying values easily. + The package clearly demonstrates the power of the functional approach: + You can combine accessors of a record and sub-records, + to make the access look like the fields of the sub-record belong to the main record. + . + Example: + . + > *Data.Accessor.Example> (first^:second^=10) (('b',7),"hallo") + > (('b',10),"hallo") + . + You can easily manipulate record fields in a 'Control.Monad.State.State' monad, + you can easily code Show instances that use the Accessor syntax + and you can parse binary streams into records. + See @Data.Accessor.Example@ for demonstration of all features. + . + It would be great if in revised Haskell versions the names of record fields + are automatically 'Data.Accessor.Accessor's + rather than plain @get@ functions. + The package @data-accessor-template@ provides Template Haskell functions + for automated generation of 'Data.Acesssor.Accessor's. +GHC-Options: -Wall +Tested-With: GHC==6.4.1 && ==6.8.2 +Hs-Source-Dirs: src +Exposed-Modules: + Data.Accessor + Data.Accessor.Basic + Data.Accessor.Show + Data.Accessor.Tuple + Data.Accessor.BinaryRead + Data.Accessor.MonadState +Other-Modules: + Data.Accessor.Example diff --git a/src/Data/Accessor.hs b/src/Data/Accessor.hs new file mode 100644 --- /dev/null +++ b/src/Data/Accessor.hs @@ -0,0 +1,93 @@ +{- | +This module provides a simple abstract data type for +a piece of a data stucture that can be read from and +written to. +In contrast to "Data.Accessor.Basic" it is intended for unqualified import. +-} +module Data.Accessor + ( Accessor, accessor, setVal, getVal, + getA, putA, (=:), modA, + (.>), (<.), + ) +where + +import qualified Data.Accessor.Basic as Accessor +import qualified Data.Accessor.MonadState as State +import Control.Monad.State (MonadState, ) + +-- |An @Accessor s a@ is an object that encodes how to +-- get and put a subject of type @a@ out of/into an object +-- of type @s@. +-- +-- In order for an instance of this data structure @a@ to be +-- an 'Accessor', it must obey the following laws: +-- +-- > getVal a (setVal a x s) = x +-- > setVal a (getVal a s) s = s +type Accessor s a = Accessor.T s a + + +-- |Construct an 'Accessor' from a @get@ and a @set@ method. +-- +accessor :: + (s -> a) {- ^ get method -} + -> (a -> s -> s) {- ^ set method -} + -> Accessor s a +accessor = flip Accessor.fromSetGet + +-- |Get a value from a record field that is specified by an Accessor +getVal :: + Accessor s a {- ^ record field -} + -> s {- ^ record -} + -> a {- ^ value of the field in the record -} +getVal = Accessor.get + +-- |Set a value of a record field that is specified by an Accessor +setVal :: + Accessor s a {- ^ record field @f@ -} + -> a {- ^ value @x@ to be set -} + -> s {- ^ original record -} + -> s {- ^ new record with field @f@ changed to @x@ -} +setVal = Accessor.set + + + +infixl 9 .> + +{- | +Accessor composition: +Combine an accessor with an accessor to a sub-field. +Speak \"stack\". +-} +(.>) :: Accessor a b -> Accessor b c -> Accessor a c +(.>) = (Accessor..>) + +infixr 9 <. +{- | +Accessor composition the other direction. + +> (<.) = flip (.>) +-} +(<.) :: Accessor b c -> Accessor a b -> Accessor a c +(<.) = (Accessor.<.) + + + +infix 1 =: +-- |An \"assignment operator\" for state monads. +-- +-- > (=:) = putA +(=:) :: MonadState s m => Accessor s a -> a -> m () +(=:) = putA + +-- |A structural dereference function for state monads. +getA :: MonadState s m => Accessor s a -> m a +getA = State.get + +-- |A structural assignment function for state monads. +putA :: MonadState s m => Accessor s a -> a -> m () +putA = State.set + +-- |A structural modification function for state monads. +modA :: MonadState s m => Accessor s a -> (a -> a) -> m () +modA = State.modify diff --git a/src/Data/Accessor/Basic.hs b/src/Data/Accessor/Basic.hs new file mode 100644 --- /dev/null +++ b/src/Data/Accessor/Basic.hs @@ -0,0 +1,124 @@ +{- | +This module defines the @Accessor@ type. +It should be imported with qualification. +-} +module Data.Accessor.Basic ( + T, fromSetGet, fromLens, + set, setMany, compose, (^=), + get, (^.), + modify, (^:), + ($%), (<.), (.>), + ) where + +{- | +The access functions we propose, look very similar to those +needed for List.mapAccumL (but parameter order is swapped) and State monad. +They get the new value of the field and the record +and return the old value of the field and the record with the updated field. +-} +newtype T r a = Cons {decons :: a -> r -> (a, r)} + +fromSetGet :: (a -> r -> r) -> (r -> a) -> T r a +fromSetGet setF getF = + Cons $ \x r -> (getF r, setF x r) + +fromLens :: (r -> (a, a -> r)) -> T r a +fromLens lens = + Cons $ \ x r -> let (y,f) = lens r in (y, f x) + +{- * Access helper functions similar to State methods -} + +{- | Set the value of a field. -} +set :: T r a -> a -> r -> r +set f x = snd . decons f x + + +infixr 5 ^=, ^: + +infixl 0 $% + + +{- | +'set' as infix operator. +This lets us write @first ^= 2+3 $ second ^= 5+7 $ record@. +-} +(^=) :: T r a -> a -> (r -> r) +(^=) = set + +{- | Set many fields at once. + +This function could also be used for initialisation of record, +if record value with undefined fields is provided. + +Drawback: +Since all types in a list must have the same type, +you can set only values of the same type. +-} +setMany :: [r -> (a, r)] -> r -> r +setMany = flip (foldl (\x f -> snd (f x))) + +{- | +This is a general function, +but it is especially useful for setting many values of different type at once. +-} +compose :: [r -> r] -> r -> r +compose = flip (foldl (flip id)) + +{- | Get the value of a field. -} +get :: T r a -> r -> a +get f = fst . decons f undefined + +infixl 9 ^. + +{- | +'get' as infix operator. +This lets us write @record^.field^.subfield@ +-} +(^.) :: r -> T r a -> a +(^.) = flip get + + +{- | Transform the value of a field by a function. -} +modify :: T r a -> (a -> a) -> (r -> r) +modify f g rOld = + let (a,rNew) = decons f (g a) rOld + in rNew + + +{- | +'modify' as infix operator. +This lets us write @record$%field^:subfield^:(1+)@ +or @record$%field^:subfield^:(const 1)@. +-} +(^:) :: T r a -> (a -> a) -> (r -> r) +(^:) = modify + +{- | +Flipped version of '($)'. +-} +($%) :: a -> (a -> b) -> b +($%) = flip ($) + + + +infixl 9 .> + +{- | +Accessor composition: +Combine an accessor with an accessor to a sub-field. +Speak \"stack\". +-} +(.>) :: T a b -> T b c -> T a c +(.>) f g = Cons $ \ cNew aOld -> + let (bOld, aNew) = decons f bNew aOld + (cOld, bNew) = decons g cNew bOld + in (cOld, aNew) + +infixr 9 <. +{- | +Accessor composition the other direction. + +> (<.) = flip (.>) +-} +(<.) :: T b c -> T a b -> T a c +(<.) = flip (.>) diff --git a/src/Data/Accessor/BinaryRead.hs b/src/Data/Accessor/BinaryRead.hs new file mode 100644 --- /dev/null +++ b/src/Data/Accessor/BinaryRead.hs @@ -0,0 +1,81 @@ +{- | +Reading records from streams + +This is still only for demonstration and might be of not much use +and you should not rely on the interface. +-} +module Data.Accessor.BinaryRead where + +import qualified Data.Accessor.Basic as Accessor + +import qualified Control.Monad.State as State +import Control.Monad.State (MonadState, StateT, ) +import Data.Word (Word8, ) +import Data.Char (chr, ) + +import Prelude hiding (any) + + +type Stream = [Word8] + +class C a where + any :: ByteSource source => source a + +class Monad source => ByteSource source where + readWord8 :: source Word8 + +class ByteStream s where + getWord8 :: Monad m => s -> m (Word8, s) + +instance ByteCompatible byte => ByteStream [byte] where + getWord8 xs = + case xs of + (c:cs) -> return (toByte c, cs) + _ -> fail "ByteStream: no more byte available" + +class ByteCompatible byte where + toByte :: byte -> Word8 + +instance ByteCompatible Word8 where + toByte = id + +instance (ByteStream s, Monad m) => ByteSource (StateT s m) where + readWord8 = + do xs <- State.get + (c,cs) <- State.lift (getWord8 xs) + State.put cs + return c + +instance C Word8 where + any = readWord8 + +instance C Char where + any = + State.liftM (chr . fromIntegral) readWord8 + +instance C Int where + any = + do c0 <- readWord8 + c1 <- readWord8 + c2 <- readWord8 + c3 <- readWord8 + return + (foldl1 (\acc d -> acc*256+d) + (map fromIntegral [c0,c1,c2,c3])) + + +newtype Parser s r = Parser {runParser :: (r, s) -> Maybe (r, s)} + + +field :: (ByteStream s, C a) => + Accessor.T r a -> Parser s r +field f = + Parser $ + uncurry (\r -> State.runStateT $ + fmap (\x -> Accessor.set f x r) any) + +record :: [Parser s r] -> Parser s r +record ps = + Parser $ flip (foldl (>>=)) (map runParser ps) . Just + +-- TOOD: writer diff --git a/src/Data/Accessor/Example.hs b/src/Data/Accessor/Example.hs new file mode 100644 --- /dev/null +++ b/src/Data/Accessor/Example.hs @@ -0,0 +1,88 @@ +module Data.Accessor.Example where + +import Data.Accessor.Basic ((.>), ($%), (^.), (^:), (^=), ) +import Data.Accessor.Tuple (first, second, ) + +import qualified Data.Accessor.Basic as Accessor +import qualified Data.Accessor.BinaryRead as Read +import qualified Data.Accessor.Show as Show + +import qualified Data.Accessor.MonadState as AState +import Control.Monad.State (State) +import Data.Char (ord, ) + +import Prelude hiding (init) + + +{- * Example accesses -} + +{- | Example of using 'set', 'get', 'modify'. -} +plain :: Int +plain = + Accessor.get second $ + Accessor.modify second succ $ + Accessor.set first 'a' $ + ('b',7) + +state :: State (Char,Int) Int +state = + do AState.set first 'a' + AState.modify second succ + AState.get second + +init :: (Char,Int) +init = + Accessor.compose + [Accessor.set first 'b', + Accessor.modify first succ, + Accessor.set second 7] + (undefined,undefined) +-- setMany [first 'b', second 7] (undefined,undefined) + +initInfix :: (Char,Int) +initInfix = + (undefined,undefined) + $% first ^= 'b' + $% first ^: succ + $% second ^= 7 + +read :: Maybe ((Char,Int), Read.Stream) +read = + Read.runParser + (Read.record [Read.field first, Read.field second]) + ((undefined,undefined), + fromIntegral (ord 'c') : 59 : 154 : 202 : 0 : []) + +infix0 :: Int +infix0 = + (('b',7),"hallo")^.first^.second + +infix1 :: ((Char, Int), String) +infix1 = + (('b',7),"hallo")$%first^:second^:(1+) + +infix2 :: ((Char, Int), String) +infix2 = + (('b',7),"hallo")$%first^:second^=10 + +infix3 :: Int +infix3 = + (('b',7),"hallo")^.(first.>second) + +infix4 :: ((Char, Int), String) +infix4 = + (('b',7),"hallo")$%(first.>second)^:(1+) + + +showsPair :: Int -> (Char, Int) -> ShowS +showsPair = + Show.showsPrec + [Show.field "first" first, + Show.field "second" second] + "init" init + +show0 :: String +show0 = showsPair 11 init "" + +show1 :: String +show1 = showsPair 5 ('d',8) "" diff --git a/src/Data/Accessor/MonadState.hs b/src/Data/Accessor/MonadState.hs new file mode 100644 --- /dev/null +++ b/src/Data/Accessor/MonadState.hs @@ -0,0 +1,15 @@ +{- | Access helper functions in a State monad -} +module Data.Accessor.MonadState where + +import qualified Data.Accessor.Basic as Accessor +import qualified Control.Monad.State as State +import Control.Monad.State (MonadState, ) + +set :: MonadState r m => Accessor.T r a -> a -> m () +set f x = State.modify (Accessor.set f x) + +get :: MonadState r m => Accessor.T r a -> m a +get f = State.gets (Accessor.get f) + +modify :: MonadState r m => Accessor.T r a -> (a -> a) -> m () +modify f g = State.modify (Accessor.modify f g) diff --git a/src/Data/Accessor/Show.hs b/src/Data/Accessor/Show.hs new file mode 100644 --- /dev/null +++ b/src/Data/Accessor/Show.hs @@ -0,0 +1,39 @@ +{- | +Support for creating Show instances using the accessors. +-} +module Data.Accessor.Show where + +import qualified Data.Accessor.Basic as Accessor + +import Data.Maybe (catMaybes) + +import qualified Text.Show as Show +import Prelude hiding (showsPrec) + + +toMaybe :: Bool -> a -> Maybe a +toMaybe False _ = Nothing +toMaybe True x = Just x + +field :: (Show a, Eq a) => + String -> Accessor.T r a -> r -> r -> Maybe ShowS +field name acc deflt record = + let x = Accessor.get acc record + in toMaybe + (x /= Accessor.get acc deflt) + (showString name . showString " ^= " . Show.showsPrec 5 x) + +showsPrec :: + [r -> r -> Maybe ShowS] -> String -> r -> Int -> r -> ShowS +showsPrec fields defltName deflt p record = + let calls = + catMaybes $ + map (\f -> f deflt record) $ + fields + in if null calls + then showString defltName + else showParen (p>0) + (foldr + (\acc s -> acc . showString " $ " . s) + (showString defltName) + calls) diff --git a/src/Data/Accessor/Tuple.hs b/src/Data/Accessor/Tuple.hs new file mode 100644 --- /dev/null +++ b/src/Data/Accessor/Tuple.hs @@ -0,0 +1,26 @@ +module Data.Accessor.Tuple where + +import qualified Data.Accessor.Basic as Accessor + +{- * Example accessors for the pair type -} + +{- | Access to the first value of a pair. -} +first :: Accessor.T (a,b) a +first = Accessor.fromSetGet (\x (_,y) -> (x,y)) fst + +{- | Access to the second value of a pair. -} +second :: Accessor.T (a,b) b +second = Accessor.fromSetGet (\y (x,_) -> (x,y)) snd + + +{- | Access to the first value of a triple. -} +first3 :: Accessor.T (a,b,c) a +first3 = Accessor.fromLens $ \(xOld,y,z) -> (xOld, \xNew -> (xNew,y,z)) + +{- | Access to the second value of a triple. -} +second3 :: Accessor.T (a,b,c) b +second3 = Accessor.fromLens $ \(x,yOld,z) -> (yOld, \yNew -> (x,yNew,z)) + +{- | Access to the third value of a triple. -} +third3 :: Accessor.T (a,b,c) c +third3 = Accessor.fromLens $ \(x,y,zOld) -> (zOld, \zNew -> (x,y,zNew))