diff --git a/syb.cabal b/syb.cabal --- a/syb.cabal +++ b/syb.cabal @@ -1,5 +1,5 @@ name: syb -version: 0.4.3 +version: 0.4.4 license: BSD3 license-file: LICENSE author: Ralf Lammel, Simon Peyton Jones, Jose Pedro Magalhaes diff --git a/tests/Bits.hs b/tests/Bits.hs --- a/tests/Bits.hs +++ b/tests/Bits.hs @@ -1,214 +1,225 @@ -{-# OPTIONS -fglasgow-exts #-} - -module Bits (tests) where - -{- - -This test exercices some oldies of generic programming, namely -encoding terms as bit streams and decoding these bit streams in turn -to obtain terms again. (This sort of function might actually be useful -for serialisation and sending companies and other terms over the -internet.) - -Here is how it works. - -A constuctor is encoded as a bit stream. To this end, we encode the -index of the constructor as a binary number of a fixed length taking -into account the maximum index for the type at hand. (Similarly, we -could view the list of constructors as a binary tree, and then encode -a constructor as the path to the constructor in this tree.) If there -is just a single constructor, as for newtypes, for example, then the -computed bit stream is empty. - -Otherwise we just recurse into subterms. - -Well, we need to handle basic datatypes in a special way. We observe -such basic datatypes by testing the maximum index to be 0 for the -datatype at hand. An efficient encoding should be tuned per basic -datatype. The following solution is generic, but it wastes space. -That is, we turn the basic value into a string relying on the general -Data API. This string can now be encoded by first converting it into a -list of bit streams at the term level, which can then be easily -encoded as a single bit stream (because lists and bits can be -encoded). - --} - -import Test.HUnit - -import Data.Generics -import Data.Char -import Data.Maybe -import Control.Monad -import CompanyDatatypes - - - ------------------------------------------------------------------------------ - - - --- | We need bits and bit streams. -data Bit = Zero | One deriving (Show, Eq, Typeable, Data) -type Bin = [Bit] - - - ------------------------------------------------------------------------------ - - - --- Compute length of bit stream for a natural -lengthNat :: Int -> Int -lengthNat x = ceiling (logBase 2 (fromIntegral (x + 1))) - - --- Encode a natural as a bit stream -varNat2bin :: Int -> Bin -varNat2bin 0 = [] -varNat2bin x = - ( ( if even x then Zero else One ) - : varNat2bin (x `div` 2) - ) - - --- Encode a natural as a bit stream of fixed length -fixedNat2bin :: Int -> Int -> Bin -fixedNat2bin 0 0 = [] -fixedNat2bin p x | p>0 = - ( ( if even x then Zero else One ) - : fixedNat2bin (p - 1) (x `div` 2) - ) - - --- Decode a natural -bin2nat :: Bin -> Int -bin2nat [] = 0 -bin2nat (Zero : bs) = 2 * (bin2nat bs) -bin2nat (One : bs) = 2 * (bin2nat bs) + 1 - - - ------------------------------------------------------------------------------ - - - --- | Generically map terms to bit streams -showBin :: Data t => t -> Bin - -showBin t - = if isAlgType myDataType - then con2bin ++ concat (gmapQ showBin t) - else showBin base - - where - - -- The datatype for introspection - myDataType = dataTypeOf t - - -- Obtain the maximum index for the type at hand - max :: Int - max = maxConstrIndex myDataType - - -- Obtain the index for the constructor at hand - idx :: Int - idx = constrIndex (toConstr t) - - -- Map basic values to strings, then to lists of bit streams - base = map (varNat2bin . ord) (showConstr (toConstr t)) - - -- Map constructors to bit streams of fixed length - con2bin = fixedNat2bin (lengthNat (max - 1)) (idx - 1) - - ------------------------------------------------------------------------------ - - - --- | A monad on bit streams -data ReadB a = ReadB (Bin -> (Maybe a, Bin)) -unReadB (ReadB f) = f - - --- It's a monad. -instance Monad ReadB where - return a = ReadB (\bs -> (Just a, bs)) - (ReadB c) >>= f = ReadB (\bs -> case c bs of - (Just a, bs') -> unReadB (f a) bs' - (Nothing, bs') -> (Nothing, bs') - ) - - --- It's a bit monad with 0 and +. -instance MonadPlus ReadB where - mzero = ReadB (\bs -> (Nothing, bs)) - (ReadB f) `mplus` (ReadB g) = ReadB (\bs -> case f bs of - (Just a, bs') -> (Just a, bs') - (Nothing, _) -> g bs - ) - - --- Read a few bits -readB :: Int -> ReadB Bin -readB x = ReadB (\bs -> if length bs >= x - then (Just (take x bs), drop x bs) - else (Nothing, bs) - ) - - - ------------------------------------------------------------------------------ - - - --- | Generically map bit streams to terms -readBin :: Data t => ReadB t -readBin = result - where - - -- The worker, which we also use as type argument - result = if isAlgType myDataType - - then do bin <- readB (lengthNat (max - 1)) - fromConstrM readBin (bin2con bin) - - else do str <- readBin - con <- str2con (map (chr . bin2nat) str) - return (fromConstr con) - - -- Determine result type - myDataType = dataTypeOf (getArg result) - where - getArg :: ReadB a -> a - getArg = undefined - - -- Obtain the maximum index for the type at hand - max :: Int - max = maxConstrIndex myDataType - - -- Convert a bit stream into a constructor - bin2con :: Bin -> Constr - bin2con bin = indexConstr myDataType ((bin2nat bin) + 1) - - -- Convert string to constructor; could fail - str2con :: String -> ReadB Constr - str2con = maybe mzero return - . readConstr myDataType - - - ------------------------------------------------------------------------------ - - - -tests = ( showBin True - , ( showBin [True] - , ( showBin (1::Int) - , ( showBin "1" - , ( showBin genCom - , ( geq genCom genCom' - )))))) ~=? output - where - genCom' = fromJust (fst (unReadB readBin (showBin genCom))) :: Company - -output = 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+{-# OPTIONS -fglasgow-exts #-} + +module Bits (tests) where + +{- + +This test exercices some oldies of generic programming, namely +encoding terms as bit streams and decoding these bit streams in turn +to obtain terms again. (This sort of function might actually be useful +for serialisation and sending companies and other terms over the +internet.) + +Here is how it works. + +A constuctor is encoded as a bit stream. To this end, we encode the +index of the constructor as a binary number of a fixed length taking +into account the maximum index for the type at hand. (Similarly, we +could view the list of constructors as a binary tree, and then encode +a constructor as the path to the constructor in this tree.) If there +is just a single constructor, as for newtypes, for example, then the +computed bit stream is empty. + +Otherwise we just recurse into subterms. + +Well, we need to handle basic datatypes in a special way. We observe +such basic datatypes by testing the maximum index to be 0 for the +datatype at hand. An efficient encoding should be tuned per basic +datatype. The following solution is generic, but it wastes space. +That is, we turn the basic value into a string relying on the general +Data API. This string can now be encoded by first converting it into a +list of bit streams at the term level, which can then be easily +encoded as a single bit stream (because lists and bits can be +encoded). + +-} + +import Test.HUnit + +import Data.Generics +import Data.Char +import Data.Maybe +import Control.Applicative (Alternative(..), Applicative(..)) +import Control.Monad +import CompanyDatatypes + + + +----------------------------------------------------------------------------- + + + +-- | We need bits and bit streams. +data Bit = Zero | One deriving (Show, Eq, Typeable, Data) +type Bin = [Bit] + + + +----------------------------------------------------------------------------- + + + +-- Compute length of bit stream for a natural +lengthNat :: Int -> Int +lengthNat x = ceiling (logBase 2 (fromIntegral (x + 1))) + + +-- Encode a natural as a bit stream +varNat2bin :: Int -> Bin +varNat2bin 0 = [] +varNat2bin x = + ( ( if even x then Zero else One ) + : varNat2bin (x `div` 2) + ) + + +-- Encode a natural as a bit stream of fixed length +fixedNat2bin :: Int -> Int -> Bin +fixedNat2bin 0 0 = [] +fixedNat2bin p x | p>0 = + ( ( if even x then Zero else One ) + : fixedNat2bin (p - 1) (x `div` 2) + ) + + +-- Decode a natural +bin2nat :: Bin -> Int +bin2nat [] = 0 +bin2nat (Zero : bs) = 2 * (bin2nat bs) +bin2nat (One : bs) = 2 * (bin2nat bs) + 1 + + + +----------------------------------------------------------------------------- + + + +-- | Generically map terms to bit streams +showBin :: Data t => t -> Bin + +showBin t + = if isAlgType myDataType + then con2bin ++ concat (gmapQ showBin t) + else showBin base + + where + + -- The datatype for introspection + myDataType = dataTypeOf t + + -- Obtain the maximum index for the type at hand + max :: Int + max = maxConstrIndex myDataType + + -- Obtain the index for the constructor at hand + idx :: Int + idx = constrIndex (toConstr t) + + -- Map basic values to strings, then to lists of bit streams + base = map (varNat2bin . ord) (showConstr (toConstr t)) + + -- Map constructors to bit streams of fixed length + con2bin = fixedNat2bin (lengthNat (max - 1)) (idx - 1) + + +----------------------------------------------------------------------------- + + + +-- | A monad on bit streams +data ReadB a = ReadB (Bin -> (Maybe a, Bin)) +unReadB (ReadB f) = f + +instance Functor ReadB where + fmap = liftM + +instance Applicative ReadB where + pure = return + (<*>) = ap + +instance Alternative ReadB where + (<|>) = mplus + empty = mzero + +-- It's a monad. +instance Monad ReadB where + return a = ReadB (\bs -> (Just a, bs)) + (ReadB c) >>= f = ReadB (\bs -> case c bs of + (Just a, bs') -> unReadB (f a) bs' + (Nothing, bs') -> (Nothing, bs') + ) + + +-- It's a bit monad with 0 and +. +instance MonadPlus ReadB where + mzero = ReadB (\bs -> (Nothing, bs)) + (ReadB f) `mplus` (ReadB g) = ReadB (\bs -> case f bs of + (Just a, bs') -> (Just a, bs') + (Nothing, _) -> g bs + ) + + +-- Read a few bits +readB :: Int -> ReadB Bin +readB x = ReadB (\bs -> if length bs >= x + then (Just (take x bs), drop x bs) + else (Nothing, bs) + ) + + + +----------------------------------------------------------------------------- + + + +-- | Generically map bit streams to terms +readBin :: Data t => ReadB t +readBin = result + where + + -- The worker, which we also use as type argument + result = if isAlgType myDataType + + then do bin <- readB (lengthNat (max - 1)) + fromConstrM readBin (bin2con bin) + + else do str <- readBin + con <- str2con (map (chr . bin2nat) str) + return (fromConstr con) + + -- Determine result type + myDataType = dataTypeOf (getArg result) + where + getArg :: ReadB a -> a + getArg = undefined + + -- Obtain the maximum index for the type at hand + max :: Int + max = maxConstrIndex myDataType + + -- Convert a bit stream into a constructor + bin2con :: Bin -> Constr + bin2con bin = indexConstr myDataType ((bin2nat bin) + 1) + + -- Convert string to constructor; could fail + str2con :: String -> ReadB Constr + str2con = maybe mzero return + . readConstr myDataType + + + +----------------------------------------------------------------------------- + + + +tests = ( showBin True + , ( showBin [True] + , ( showBin (1::Int) + , ( showBin "1" + , ( showBin genCom + , ( geq genCom genCom' + )))))) ~=? output + where + genCom' = fromJust (fst (unReadB readBin (showBin genCom))) :: Company + +output = 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diff --git a/tests/Encode.hs b/tests/Encode.hs --- a/tests/Encode.hs +++ b/tests/Encode.hs @@ -1,81 +1,88 @@ -{-# OPTIONS -fglasgow-exts #-} - --- A bit more test code for the 2nd boilerplate paper. --- These are downscaled versions of library functionality or real test cases. --- We just wanted to typecheck the fragments as shown in the paper. - -module Encode () where - -import Data.Generics - -data Bit = Zero | One - ------------------------------------------------------------------------------- --- Sec. 3.2 - -data2bits :: Data a => a -> [Bit] -data2bits t = encodeCon (dataTypeOf t) (toConstr t) - ++ concat (gmapQ data2bits t) - --- The encoder for constructors -encodeCon :: DataType -> Constr -> [Bit] -encodeCon ty con = natToBin (max-1) (idx-1) - where - max = maxConstrIndex ty - idx = constrIndex con - - -natToBin :: Int -> Int -> [Bit] -natToBin = undefined - ------------------------------------------------------------------------------- --- Sec. 3.3 - -data State -- Abstract -initState :: State -encodeCon' :: DataType -> Constr - -> State -> (State, [Bit]) - -initState = undefined -encodeCon' = undefined - -data2bits' :: Data a => a -> [Bit] -data2bits' t = snd (show_bin t initState) - -show_bin :: Data a => a -> State -> (State, [Bit]) -show_bin t st = (st2, con_bits ++ args_bits) - where - (st1, con_bits) = encodeCon' (dataTypeOf t) - (toConstr t) st - (st2, args_bits) = foldr do_arg (st1,[]) - enc_args - - enc_args :: [State -> (State,[Bit])] - enc_args = gmapQ show_bin t - - do_arg fn (st,bits) = (st', bits' ++ bits) - where - (st', bits') = fn st - - ------------------------------------------------------------------------------- --- Sec. 3.3 cont'd - -data EncM a -- The encoder monad -instance Monad EncM - where - return = undefined - c >>= f = undefined - -runEnc :: EncM () -> [Bit] -emitCon :: DataType -> Constr -> EncM () - -runEnc = undefined -emitCon = undefined - -data2bits'' :: Data a => a -> [Bit] -data2bits'' t = runEnc (emit t) - -emit :: Data a => a -> EncM () -emit t = do { emitCon (dataTypeOf t) (toConstr t) - ; sequence_ (gmapQ emit t) } +{-# OPTIONS -fglasgow-exts #-} + +-- A bit more test code for the 2nd boilerplate paper. +-- These are downscaled versions of library functionality or real test cases. +-- We just wanted to typecheck the fragments as shown in the paper. + +module Encode () where + +import Control.Applicative (Applicative(..)) +import Control.Monad (ap, liftM) +import Data.Generics + +data Bit = Zero | One + +------------------------------------------------------------------------------ +-- Sec. 3.2 + +data2bits :: Data a => a -> [Bit] +data2bits t = encodeCon (dataTypeOf t) (toConstr t) + ++ concat (gmapQ data2bits t) + +-- The encoder for constructors +encodeCon :: DataType -> Constr -> [Bit] +encodeCon ty con = natToBin (max-1) (idx-1) + where + max = maxConstrIndex ty + idx = constrIndex con + + +natToBin :: Int -> Int -> [Bit] +natToBin = undefined + +------------------------------------------------------------------------------ +-- Sec. 3.3 + +data State -- Abstract +initState :: State +encodeCon' :: DataType -> Constr + -> State -> (State, [Bit]) + +initState = undefined +encodeCon' = undefined + +data2bits' :: Data a => a -> [Bit] +data2bits' t = snd (show_bin t initState) + +show_bin :: Data a => a -> State -> (State, [Bit]) +show_bin t st = (st2, con_bits ++ args_bits) + where + (st1, con_bits) = encodeCon' (dataTypeOf t) + (toConstr t) st + (st2, args_bits) = foldr do_arg (st1,[]) + enc_args + + enc_args :: [State -> (State,[Bit])] + enc_args = gmapQ show_bin t + + do_arg fn (st,bits) = (st', bits' ++ bits) + where + (st', bits') = fn st + + +------------------------------------------------------------------------------ +-- Sec. 3.3 cont'd + +data EncM a -- The encoder monad +instance Functor EncM where + fmap = liftM +instance Applicative EncM where + pure = return + (<*>) = ap +instance Monad EncM + where + return = undefined + c >>= f = undefined + +runEnc :: EncM () -> [Bit] +emitCon :: DataType -> Constr -> EncM () + +runEnc = undefined +emitCon = undefined + +data2bits'' :: Data a => a -> [Bit] +data2bits'' t = runEnc (emit t) + +emit :: Data a => a -> EncM () +emit t = do { emitCon (dataTypeOf t) (toConstr t) + ; sequence_ (gmapQ emit t) } diff --git a/tests/Ext1.hs b/tests/Ext1.hs --- a/tests/Ext1.hs +++ b/tests/Ext1.hs @@ -1,124 +1,128 @@ -{-# OPTIONS -fglasgow-exts #-} - -module Ext1 (tests) where - -{- - -This example records some experiments with polymorphic datatypes. - --} - -import Test.HUnit - -import Data.Generics -import GHC.Base - - --- Unsafe coerce -unsafeCoerce :: a -> b -unsafeCoerce = unsafeCoerce# - - --- Handy type constructors -newtype ID x = ID { unID :: x } -newtype CONST c a = CONST { unCONST :: c } - - --- Extension of a query with a para. poly. list case -extListQ' :: Data d - => (d -> q) - -> (forall d. [d] -> q) - -> d -> q -extListQ' def ext d = - if isList d - then ext (unsafeCoerce d) - else def d - - --- Test extListQ' -foo1 :: Data d => d -> Int -foo1 = const 0 `extListQ'` length -t1 = foo1 True -- should count as 0 -t2 = foo1 [True,True] -- should count as 2 - - --- Infeasible extension of a query with a data-polymorphic list case -extListQ'' :: Data d - => (d -> q) - -> (forall d. Data d => [d] -> q) - -> d -> q -extListQ'' def ext d = - if isList d - then undefined -- hard to avoid an ambiguous type - else def d - - --- Test extListQ from Data.Generics.Aliases -foo2 :: Data a => a -> Int -foo2 = const 0 `ext1Q` list - where - list :: Data a => [a] -> Int - list l = foldr (+) 0 $ map glength l - -t3 = foo2 (True,True) -- should count as 0 -t4 = foo2 [(True,True),(True,True)] -- should count as 2+2=4 - - --- Customisation for lists without type cast -foo3 :: Data a => a -> Int -foo3 x = if isList x - then foldr (+) 0 $ gmapListQ glength x - else 0 - -t5 = foo3 (True,True) -- should count as 0 -t6 = foo3 [(True,True),(True,True)] -- should count as 2+2=4 - - --- Test for list datatype -isList :: Data a => a -> Bool -isList x = typeRepTyCon (typeOf x) == - typeRepTyCon (typeOf (undefined::[()])) - - --- Test for nil -isNil :: Data a => a -> Bool -isNil x = toConstr x == toConstr ([]::[()]) - - --- Test for cons -isCons :: Data a => a -> Bool -isCons x = toConstr x == toConstr (():[]) - - --- gmapQ for polymorphic lists -gmapListQ :: forall a q. Data a => (forall a. Data a => a -> q) -> a -> [q] -gmapListQ f x = - if not $ isList x - then error "gmapListQ" - else if isNil x - then [] - else if isCons x - then ( gmapQi 0 f x : gmapQi 1 (gmapListQ f) x ) - else error "gmapListQ" - - --- Build nil -mkNil :: Data a => a -mkNil = fromConstr $ toConstr ([]::[()]) - - --- Build cons -mkCons :: Data a => a -mkCons = fromConstr $ toConstr ((undefined:undefined)::[()]) - - --- Main function for testing -tests = ( t1 - , ( t2 - , ( t3 - , ( t4 - , ( t5 - , ( t6 - )))))) ~=? output - -output = (0,(2,(0,(4,(0,4))))) +{-# OPTIONS -fglasgow-exts #-} +{-# LANGUAGE CPP #-} + +module Ext1 (tests) where + +{- + +This example records some experiments with polymorphic datatypes. + +-} + +import Test.HUnit + +import Data.Generics +#if MIN_VERSION_base(4,8,0) +import GHC.Base hiding(foldr) +#else +import GHC.Base +#endif + +-- Unsafe coerce +unsafeCoerce :: a -> b +unsafeCoerce = unsafeCoerce# + + +-- Handy type constructors +newtype ID x = ID { unID :: x } +newtype CONST c a = CONST { unCONST :: c } + + +-- Extension of a query with a para. poly. list case +extListQ' :: Data d + => (d -> q) + -> (forall d. [d] -> q) + -> d -> q +extListQ' def ext d = + if isList d + then ext (unsafeCoerce d) + else def d + + +-- Test extListQ' +foo1 :: Data d => d -> Int +foo1 = const 0 `extListQ'` length +t1 = foo1 True -- should count as 0 +t2 = foo1 [True,True] -- should count as 2 + + +-- Infeasible extension of a query with a data-polymorphic list case +extListQ'' :: Data d + => (d -> q) + -> (forall d. Data d => [d] -> q) + -> d -> q +extListQ'' def ext d = + if isList d + then undefined -- hard to avoid an ambiguous type + else def d + + +-- Test extListQ from Data.Generics.Aliases +foo2 :: Data a => a -> Int +foo2 = const 0 `ext1Q` list + where + list :: Data a => [a] -> Int + list l = foldr (+) 0 $ map glength l + +t3 = foo2 (True,True) -- should count as 0 +t4 = foo2 [(True,True),(True,True)] -- should count as 2+2=4 + + +-- Customisation for lists without type cast +foo3 :: Data a => a -> Int +foo3 x = if isList x + then foldr (+) 0 $ gmapListQ glength x + else 0 + +t5 = foo3 (True,True) -- should count as 0 +t6 = foo3 [(True,True),(True,True)] -- should count as 2+2=4 + + +-- Test for list datatype +isList :: Data a => a -> Bool +isList x = typeRepTyCon (typeOf x) == + typeRepTyCon (typeOf (undefined::[()])) + + +-- Test for nil +isNil :: Data a => a -> Bool +isNil x = toConstr x == toConstr ([]::[()]) + + +-- Test for cons +isCons :: Data a => a -> Bool +isCons x = toConstr x == toConstr (():[]) + + +-- gmapQ for polymorphic lists +gmapListQ :: forall a q. Data a => (forall a. Data a => a -> q) -> a -> [q] +gmapListQ f x = + if not $ isList x + then error "gmapListQ" + else if isNil x + then [] + else if isCons x + then ( gmapQi 0 f x : gmapQi 1 (gmapListQ f) x ) + else error "gmapListQ" + + +-- Build nil +mkNil :: Data a => a +mkNil = fromConstr $ toConstr ([]::[()]) + + +-- Build cons +mkCons :: Data a => a +mkCons = fromConstr $ toConstr ((undefined:undefined)::[()]) + + +-- Main function for testing +tests = ( t1 + , ( t2 + , ( t3 + , ( t4 + , ( t5 + , ( t6 + )))))) ~=? output + +output = (0,(2,(0,(4,(0,4))))) diff --git a/tests/GRead.hs b/tests/GRead.hs --- a/tests/GRead.hs +++ b/tests/GRead.hs @@ -1,45 +1,45 @@ -{-# OPTIONS -fglasgow-exts #-} - -module GRead (tests) where - -{- - -The following examples achieve branch coverage for the various -productions in the definition of gread. Also, negative test cases are -provided; see str2 and str3. Also, the potential of heading or -trailing spaces as well incomplete parsing of the input is exercised; -see str5. - --} - -import Test.HUnit - -import Data.Generics - -str1 = "(True)" -- reads fine as a Bool -str2 = "(Treu)" -- invalid constructor -str3 = "True" -- lacks parentheses -str4 = "(1)" -- could be an Int -str5 = "( 2 ) ..." -- could be an Int with some trailing left-over -str6 = "([])" -- test empty list -str7 = "((:)" ++ " " ++ str4 ++ " " ++ str6 ++ ")" - -tests = show ( ( [ gread str1, - gread str2, - gread str3 - ] - , [ gread str4, - gread str5 - ] - , [ gread str6, - gread str7 - ] - ) - :: ( [[(Bool, String)]] - , [[(Int, String)]] - , [[([Int], String)]] - ) - ) ~=? output - -output = show - ([[(True,"")],[],[]],[[(1,"")],[(2,"...")]],[[([],"")],[([1],"")]]) +{-# OPTIONS -fglasgow-exts #-} + +module GRead (tests) where + +{- + +The following examples achieve branch coverage for the various +productions in the definition of gread. Also, negative test cases are +provided; see str2 and str3. Also, the potential of heading or +trailing spaces as well incomplete parsing of the input is exercised; +see str5. + +-} + +import Test.HUnit + +import Data.Generics + +str1 = "(True)" -- reads fine as a Bool +str2 = "(Treu)" -- invalid constructor +str3 = "True" -- lacks parentheses +str4 = "(1)" -- could be an Int +str5 = "( 2 ) ..." -- could be an Int with some trailing left-over +str6 = "([])" -- test empty list +str7 = "((:)" ++ " " ++ str4 ++ " " ++ str6 ++ ")" + +tests = show ( ( [ gread str1, + gread str2, + gread str3 + ] + , [ gread str4, + gread str5 + ] + , [ gread str6, + gread str7 + ] + ) + :: ( [[(Bool, String)]] + , [[(Int, String)]] + , [[([Int], String)]] + ) + ) ~=? output + +output = show + ([[(True,"")],[],[]],[[(1,"")],[(2,"...")]],[[([],"")],[([1],"")]]) diff --git a/tests/GRead2.hs b/tests/GRead2.hs --- a/tests/GRead2.hs +++ b/tests/GRead2.hs @@ -1,66 +1,75 @@ -{-# OPTIONS -fglasgow-exts #-} - -module GRead2 () where - -{- - -For the discussion in the 2nd boilerplate paper, -we favour some simplified generic read, which is checked to compile. -For the full/real story see Data.Generics.Text. - --} - -import Data.Generics - -gread :: Data a => String -> Maybe a -gread input = runDec input readM - --- The decoder monad -newtype DecM a = D (String -> Maybe (String, a)) - -instance Monad DecM where - return a = D (\s -> Just (s,a)) - (D m) >>= k = D (\s -> - case m s of - Nothing -> Nothing - Just (s1,a) -> let D n = k a - in n s1) - -runDec :: String -> DecM a -> Maybe a -runDec input (D m) = do (_,x) <- m input - return x - -parseConstr :: DataType -> DecM Constr -parseConstr ty = D (\s -> - match s (dataTypeConstrs ty)) - where - match :: String -> [Constr] - -> Maybe (String, Constr) - match _ [] = Nothing - match input (con:cons) - | take n input == showConstr con - = Just (drop n input, con) - | otherwise - = match input cons - where - n = length (showConstr con) - - -readM :: forall a. Data a => DecM a -readM = read - where - read :: DecM a - read = do { let val = argOf read - ; let ty = dataTypeOf val - ; constr <- parseConstr ty - ; let con::a = fromConstr constr - ; gmapM (\_ -> readM) con } - -argOf :: c a -> a -argOf = undefined - -yareadM :: forall a. Data a => DecM a -yareadM = do { let ty = dataTypeOf (undefined::a) - ; constr <- parseConstr ty - ; let con::a = fromConstr constr - ; gmapM (\_ -> yareadM) con } +{-# OPTIONS -fglasgow-exts #-} + +module GRead2 () where + +{- + +For the discussion in the 2nd boilerplate paper, +we favour some simplified generic read, which is checked to compile. +For the full/real story see Data.Generics.Text. + +-} + +import Control.Applicative (Applicative(..)) +import Control.Monad (ap, liftM) +import Data.Generics + +gread :: Data a => String -> Maybe a +gread input = runDec input readM + +-- The decoder monad +newtype DecM a = D (String -> Maybe (String, a)) + +instance Functor DecM where + fmap = liftM + +instance Applicative DecM where + pure = return + (<*>) = ap + +instance Monad DecM where + return a = D (\s -> Just (s,a)) + (D m) >>= k = D (\s -> + case m s of + Nothing -> Nothing + Just (s1,a) -> let D n = k a + in n s1) + +runDec :: String -> DecM a -> Maybe a +runDec input (D m) = do (_,x) <- m input + return x + +parseConstr :: DataType -> DecM Constr +parseConstr ty = D (\s -> + match s (dataTypeConstrs ty)) + where + match :: String -> [Constr] + -> Maybe (String, Constr) + match _ [] = Nothing + match input (con:cons) + | take n input == showConstr con + = Just (drop n input, con) + | otherwise + = match input cons + where + n = length (showConstr con) + + +readM :: forall a. Data a => DecM a +readM = read + where + read :: DecM a + read = do { let val = argOf read + ; let ty = dataTypeOf val + ; constr <- parseConstr ty + ; let con::a = fromConstr constr + ; gmapM (\_ -> readM) con } + +argOf :: c a -> a +argOf = undefined + +yareadM :: forall a. Data a => DecM a +yareadM = do { let ty = dataTypeOf (undefined::a) + ; constr <- parseConstr ty + ; let con::a = fromConstr constr + ; gmapM (\_ -> yareadM) con } diff --git a/tests/Perm.hs b/tests/Perm.hs --- a/tests/Perm.hs +++ b/tests/Perm.hs @@ -1,127 +1,139 @@ -{-# OPTIONS -fglasgow-exts #-} - -module Perm (tests) where - -{- - -This module illustrates permutation phrases. -Disclaimer: this is a perhaps naive, certainly undebugged example. - --} - -import Test.HUnit - -import Control.Monad -import Data.Generics - ---------------------------------------------------------------------------- --- We want to read terms of type T3 regardless of the order T1 and T2. ---------------------------------------------------------------------------- - -data T1 = T1 deriving (Show, Eq, Typeable, Data) -data T2 = T2 deriving (Show, Eq, Typeable, Data) -data T3 = T3 T1 T2 deriving (Show, Eq, Typeable, Data) - - ---------------------------------------------------------------------------- --- A silly monad that we use to read lists of constructor strings. ---------------------------------------------------------------------------- - --- Type constructor -newtype ReadT a = ReadT { unReadT :: [String] -> Maybe ([String],a) } - - - --- Run a computation -runReadT x y = case unReadT x y of - Just ([],y) -> Just y - _ -> Nothing - --- Read one string -readT :: ReadT String -readT = ReadT (\x -> if null x - then Nothing - else Just (tail x, head x) - ) - --- ReadT is a monad! -instance Monad ReadT where - return x = ReadT (\y -> Just (y,x)) - c >>= f = ReadT (\x -> case unReadT c x of - Nothing -> Nothing - Just (x', a) -> unReadT (f a) x' - ) - --- ReadT also accommodates mzero and mplus! -instance MonadPlus ReadT where - mzero = ReadT (const Nothing) - f `mplus` g = ReadT (\x -> case unReadT f x of - Nothing -> unReadT g x - y -> y - ) - - ---------------------------------------------------------------------------- --- A helper type to appeal to predicative type system. ---------------------------------------------------------------------------- - -newtype GenM = GenM { unGenM :: forall a. Data a => a -> ReadT a } - - ---------------------------------------------------------------------------- --- The function that reads and copes with all permutations. ---------------------------------------------------------------------------- - -buildT :: forall a. Data a => ReadT a -buildT = result - - where - result = do str <- readT - con <- string2constr str - ske <- return $ fromConstr con - fs <- return $ gmapQ buildT' ske - perm [] fs ske - - -- Determine type of data to be constructed - myType = myTypeOf result - where - myTypeOf :: forall a. ReadT a -> a - myTypeOf = undefined - - -- Turn string into constructor - string2constr str = maybe mzero - return - (readConstr (dataTypeOf myType) str) - - -- Specialise buildT per kid type - buildT' :: forall a. Data a => a -> GenM - buildT' (_::a) = GenM (const mzero `extM` const (buildT::ReadT a)) - - -- The permutation exploration function - perm :: forall a. Data a => [GenM] -> [GenM] -> a -> ReadT a - perm [] [] a = return a - perm fs [] a = perm [] fs a - perm fs (f:fs') a = ( - do a' <- gmapMo (unGenM f) a - perm fs fs' a' - ) - `mplus` - ( - do guard (not (null fs')) - perm (f:fs) fs' a - ) - - ---------------------------------------------------------------------------- --- The main function for testing ---------------------------------------------------------------------------- - -tests = - ( runReadT buildT ["T1"] :: Maybe T1 -- should parse fine - , ( runReadT buildT ["T2"] :: Maybe T2 -- should parse fine - , ( runReadT buildT ["T3","T1","T2"] :: Maybe T3 -- should parse fine - , ( runReadT buildT ["T3","T2","T1"] :: Maybe T3 -- should parse fine - , ( runReadT buildT ["T3","T2","T2"] :: Maybe T3 -- should fail - ))))) ~=? output - -output = (Just T1,(Just T2,(Just (T3 T1 T2),(Just (T3 T1 T2),Nothing)))) +{-# OPTIONS -fglasgow-exts #-} + +module Perm (tests) where + +{- + +This module illustrates permutation phrases. +Disclaimer: this is a perhaps naive, certainly undebugged example. + +-} + +import Test.HUnit + +import Control.Applicative (Alternative(..), Applicative(..)) +import Control.Monad +import Data.Generics + +--------------------------------------------------------------------------- +-- We want to read terms of type T3 regardless of the order T1 and T2. +--------------------------------------------------------------------------- + +data T1 = T1 deriving (Show, Eq, Typeable, Data) +data T2 = T2 deriving (Show, Eq, Typeable, Data) +data T3 = T3 T1 T2 deriving (Show, Eq, Typeable, Data) + + +--------------------------------------------------------------------------- +-- A silly monad that we use to read lists of constructor strings. +--------------------------------------------------------------------------- + +-- Type constructor +newtype ReadT a = ReadT { unReadT :: [String] -> Maybe ([String],a) } + + + +-- Run a computation +runReadT x y = case unReadT x y of + Just ([],y) -> Just y + _ -> Nothing + +-- Read one string +readT :: ReadT String +readT = ReadT (\x -> if null x + then Nothing + else Just (tail x, head x) + ) + +instance Functor ReadT where + fmap = liftM + +instance Applicative ReadT where + pure = return + (<*>) = ap + +instance Alternative ReadT where + (<|>) = mplus + empty = mzero + +-- ReadT is a monad! +instance Monad ReadT where + return x = ReadT (\y -> Just (y,x)) + c >>= f = ReadT (\x -> case unReadT c x of + Nothing -> Nothing + Just (x', a) -> unReadT (f a) x' + ) + +-- ReadT also accommodates mzero and mplus! +instance MonadPlus ReadT where + mzero = ReadT (const Nothing) + f `mplus` g = ReadT (\x -> case unReadT f x of + Nothing -> unReadT g x + y -> y + ) + + +--------------------------------------------------------------------------- +-- A helper type to appeal to predicative type system. +--------------------------------------------------------------------------- + +newtype GenM = GenM { unGenM :: forall a. Data a => a -> ReadT a } + + +--------------------------------------------------------------------------- +-- The function that reads and copes with all permutations. +--------------------------------------------------------------------------- + +buildT :: forall a. Data a => ReadT a +buildT = result + + where + result = do str <- readT + con <- string2constr str + ske <- return $ fromConstr con + fs <- return $ gmapQ buildT' ske + perm [] fs ske + + -- Determine type of data to be constructed + myType = myTypeOf result + where + myTypeOf :: forall a. ReadT a -> a + myTypeOf = undefined + + -- Turn string into constructor + string2constr str = maybe mzero + return + (readConstr (dataTypeOf myType) str) + + -- Specialise buildT per kid type + buildT' :: forall a. Data a => a -> GenM + buildT' (_::a) = GenM (const mzero `extM` const (buildT::ReadT a)) + + -- The permutation exploration function + perm :: forall a. Data a => [GenM] -> [GenM] -> a -> ReadT a + perm [] [] a = return a + perm fs [] a = perm [] fs a + perm fs (f:fs') a = ( + do a' <- gmapMo (unGenM f) a + perm fs fs' a' + ) + `mplus` + ( + do guard (not (null fs')) + perm (f:fs) fs' a + ) + + +--------------------------------------------------------------------------- +-- The main function for testing +--------------------------------------------------------------------------- + +tests = + ( runReadT buildT ["T1"] :: Maybe T1 -- should parse fine + , ( runReadT buildT ["T2"] :: Maybe T2 -- should parse fine + , ( runReadT buildT ["T3","T1","T2"] :: Maybe T3 -- should parse fine + , ( runReadT buildT ["T3","T2","T1"] :: Maybe T3 -- should parse fine + , ( runReadT buildT ["T3","T2","T2"] :: Maybe T3 -- should fail + ))))) ~=? output + +output = (Just T1,(Just T2,(Just (T3 T1 T2),(Just (T3 T1 T2),Nothing)))) diff --git a/tests/Reify.hs b/tests/Reify.hs --- a/tests/Reify.hs +++ b/tests/Reify.hs @@ -1,413 +1,413 @@ -{-# OPTIONS -fglasgow-exts #-} - -module Reify (tests) where - -{- - -The following examples illustrate the reification facilities for type -structure. Most notably, we generate shallow terms using the depth of -types and constructors as means to steer the generation. - --} - -import Test.HUnit - -import Data.Maybe -import Data.Generics -import Control.Monad.State -import CompanyDatatypes - - - ------------------------------------------------------------------------------- --- --- Encoding types as values; some other way. --- ------------------------------------------------------------------------------- - -{- - -This group provides a style of encoding types as values and using -them. This style is seen as an alternative to the pragmatic style used -in Data.Typeable.typeOf and elsewhere, i.e., simply use an "undefined" -to denote a type argument. This pragmatic style suffers from lack -of robustness: one feels tempted to pattern match on undefineds. -Maybe Data.Typeable.typeOf etc. should be rewritten accordingly. - --} - - --- | Type as values to stipulate use of undefineds -type TypeVal a = a -> () - - --- | The value that denotes a type -typeVal :: TypeVal a -typeVal = const () - - --- | Test for type equivalence -sameType :: (Typeable a, Typeable b) => TypeVal a -> TypeVal b -> Bool -sameType tva tvb = typeOf (type2val tva) == - typeOf (type2val tvb) - - --- | Map a value to its type -val2type :: a -> TypeVal a -val2type _ = typeVal - - --- | Stipulate this idiom! -type2val :: TypeVal a -> a -type2val _ = undefined - - --- | Constrain a type -withType :: a -> TypeVal a -> a -withType x _ = x - - --- | The argument type of a function -argType :: (a -> b) -> TypeVal a -argType _ = typeVal - - --- | The result type of a function -resType :: (a -> b) -> TypeVal b -resType _ = typeVal - - --- | The parameter type of type constructor -paraType :: t a -> TypeVal a -paraType _ = typeVal - - --- Type functions, --- i.e., functions mapping types to values --- -type TypeFun a r = TypeVal a -> r - - - --- Generic type functions, --- i.e., functions mapping types to values --- -type GTypeFun r = forall a. Data a => TypeFun a r - - - --- | Extend a type function -extType :: (Data a, Typeable r) => GTypeFun r -> TypeFun a r -> GTypeFun r -extType f x = maybe f id (cast x) - - - ------------------------------------------------------------------------------- --- --- Mapping operators to map over type structure --- ------------------------------------------------------------------------------- - - --- | Query all constructors of a given type - -gmapType :: ([(Constr,r')] -> r) - -> GTypeFun (Constr -> r') - -> GTypeFun r - -gmapType (o::[(Constr,r')] -> r) f (t::TypeVal a) - = - o $ zip cons query - - where - - -- All constructors of the given type - cons :: [Constr] - cons = if isAlgType $ dataTypeOf $ type2val t - then dataTypeConstrs $ dataTypeOf $ type2val t - else [] - - -- Query constructors - query :: [r'] - query = map (f t) cons - - --- | Query all subterm types of a given constructor - -gmapConstr :: ([r] -> r') - -> GTypeFun r - -> GTypeFun (Constr -> r') - -gmapConstr (o::[r] -> r') f (t::TypeVal a) c - = - o $ query - - where - - -- Term for the given constructor - term :: a - term = fromConstr c - - -- Query subterm types - query :: [r] - query = gmapQ (f . val2type) term - - --- | Compute arity of a given constructor -constrArity :: GTypeFun (Constr -> Int) -constrArity t c = glength $ withType (fromConstr c) t - - --- | Query all immediate subterm types of a given type -gmapSubtermTypes :: (Data a, Typeable r) - => (r -> r -> r) -> r -> GTypeFun r -> TypeVal a -> r -gmapSubtermTypes o (r::r) f (t::TypeVal a) - = - reduce (concat (map (gmapQ (query . val2type)) terms)) - (GTypeFun' f) - - where - - -- All constructors of the given type - cons :: [Constr] - cons = if isAlgType $ dataTypeOf $ type2val t - then dataTypeConstrs $ dataTypeOf $ type2val t - else [] - - -- Terms for all constructors - terms :: [a] - terms = map fromConstr cons - - -- Query a subterm type - query :: Data b => TypeVal b -> GTypeFun' r -> (r,GTypeFun' r) - query t f = (unGTypeFun' f t, GTypeFun' (disable t (unGTypeFun' f))) - - -- Constant out given type - disable :: Data b => TypeVal b -> GTypeFun r -> GTypeFun r - disable (t::TypeVal b) f = f `extType` \(_::TypeVal b) -> r - - -- Reduce all subterm types - reduce :: [GTypeFun' r -> (r,GTypeFun' r)] -> GTypeFun' r -> r - reduce [] _ = r - reduce (xy:z) g = fst (xy g) `o` reduce z (snd (xy g)) - - --- First-class polymorphic variation on GTypeFun -newtype GTypeFun' r = GTypeFun' (GTypeFun r) -unGTypeFun' (GTypeFun' f) = f - - --- | Query all immediate subterm types. --- There is an extra argument to \"constant out\" the type at hand. --- This can be used to avoid cycles. - -gmapSubtermTypesConst :: (Data a, Typeable r) - => (r -> r -> r) - -> r - -> GTypeFun r - -> TypeVal a - -> r -gmapSubtermTypesConst o (r::r) f (t::TypeVal a) - = - gmapSubtermTypes o r f' t - where - f' :: GTypeFun r - f' = f `extType` \(_::TypeVal a) -> r - - --- Count all distinct subterm types -gcountSubtermTypes :: Data a => TypeVal a -> Int -gcountSubtermTypes = gmapSubtermTypes (+) (0::Int) (const 1) - - --- | A simplied variation on gmapSubtermTypes. --- Weakness: no awareness of doubles. --- Strength: easy to comprehend as it uses gmapType and gmapConstr. - -_gmapSubtermTypes :: (Data a, Typeable r) - => (r -> r -> r) -> r -> GTypeFun r -> TypeVal a -> r -_gmapSubtermTypes o (r::r) f - = - gmapType otype (gmapConstr oconstr f) - - where - - otype :: [(Constr,r)] -> r - otype = foldr (\x y -> snd x `o` y) r - - oconstr :: [r] -> r - oconstr = foldr o r - - ------------------------------------------------------------------------------- --- --- Some reifying relations on types --- ------------------------------------------------------------------------------- - - --- | Reachability relation on types, i.e., --- test if nodes of type @a@ are reachable from nodes of type @b@. --- The relation is defined to be reflexive. - -reachableType :: (Data a, Data b) => TypeVal a -> TypeVal b -> Bool -reachableType (a::TypeVal a) (b::TypeVal b) - = - or [ sameType a b - , gmapSubtermTypesConst (\x y -> or [x,y]) False (reachableType a) b - ] - - --- | Depth of a datatype as the constructor with the minimum depth. --- The outermost 'Nothing' denotes a type without constructors. --- The innermost 'Nothing' denotes potentially infinite. - -depthOfType :: GTypeFun Bool -> GTypeFun (Maybe (Constr, Maybe Int)) -depthOfType p (t::TypeVal a) - = - gmapType o f t - - where - - o :: [(Constr, Maybe Int)] -> Maybe (Constr, Maybe Int) - o l = if null l then Nothing else Just (foldr1 min' l) - - f :: GTypeFun (Constr -> Maybe Int) - f = depthOfConstr p' - - -- Specific minimum operator - min' :: (Constr, Maybe Int) -> (Constr, Maybe Int) -> (Constr, Maybe Int) - min' x (_, Nothing) = x - min' (_, Nothing) x = x - min' (c, Just i) (c', Just i') | i <= i' = (c, Just i) - min' (c, Just i) (c', Just i') = (c', Just i') - - -- Updated predicate for unblocked types - p' :: GTypeFun Bool - p' = p `extType` \(_::TypeVal a) -> False - - --- | Depth of a constructor. --- Depth is viewed as the maximum depth of all subterm types + 1. --- 'Nothing' denotes potentially infinite. - -depthOfConstr :: GTypeFun Bool -> GTypeFun (Constr -> Maybe Int) -depthOfConstr p (t::TypeVal a) c - = - gmapConstr o f t c - - where - - o :: [Maybe Int] -> Maybe Int - o = inc' . foldr max' (Just 0) - - f :: GTypeFun (Maybe Int) - f t' = if p t' - then - case depthOfType p t' of - Nothing -> Just 0 - Just (_, x) -> x - else Nothing - - -- Specific maximum operator - max' Nothing _ = Nothing - max' _ Nothing = Nothing - max' (Just i) (Just i') | i >= i' = Just i - max' (Just i) (Just i') = Just i' - - -- Specific increment operator - inc' Nothing = Nothing - inc' (Just i) = Just (i+1) - - ------------------------------------------------------------------------------- --- --- Build a shallow term --- ------------------------------------------------------------------------------- - -shallowTerm :: (forall a. Data a => Maybe a) -> (forall b. Data b => b) -shallowTerm cust - = result - where - result :: forall b. Data b => b - -- Need a type signature here to bring 'b' into scope - result = maybe gdefault id cust - where - - -- The worker, also used for type disambiguation - gdefault :: b - gdefault = case con of - Just (con, Just _) -> fromConstrB (shallowTerm cust) con - _ -> error "no shallow term!" - - -- The type to be constructed - typeVal :: TypeVal b - typeVal = val2type gdefault - - -- The most shallow constructor if any - con :: Maybe (Constr, Maybe Int) - con = depthOfType (const True) typeVal - - - --- For testing shallowTerm -shallowTermBase :: GenericR Maybe -shallowTermBase = Nothing - `extR` Just (1.23::Float) - `extR` Just ("foo"::String) - - - --- Sample datatypes -data T1 = T1a deriving (Typeable, Data) -- just a constant -data T2 = T2 T1 deriving (Typeable, Data) -- little detour -data T3 = T3a T3 | T3b T2 deriving (Typeable, Data) -- recursive case -data T4 = T4 T3 T3 deriving (Typeable, Data) -- sum matters - - - --- Sample type arguments -t0 = typeVal :: TypeVal Int -t1 = typeVal :: TypeVal T1 -t2 = typeVal :: TypeVal T2 -t3 = typeVal :: TypeVal T3 -t4 = typeVal :: TypeVal T4 -tCompany = typeVal :: TypeVal Company -tPerson = typeVal :: TypeVal Person -tEmployee = typeVal :: TypeVal Employee -tDept = typeVal :: TypeVal Dept - - - --- Test cases -test0 = t1 `reachableType` t1 -- True -test1 = t1 `reachableType` t2 -- True -test2 = t2 `reachableType` t1 -- False -test3 = t1 `reachableType` t3 -test4 = tPerson `reachableType` tCompany -test5 = gcountSubtermTypes tPerson -test6 = gcountSubtermTypes tEmployee -test7 = gcountSubtermTypes tDept -test8 = shallowTerm shallowTermBase :: Person -test9 = shallowTerm shallowTermBase :: Employee -test10 = shallowTerm shallowTermBase :: Dept - - - -tests = ( test0 - , ( test1 - , ( test2 - , ( test3 - , ( test4 - , ( test5 - , ( test6 - , ( test7 - , ( test8 - , ( test9 - , ( test10 - ))))))))))) ~=? output - -output = (True,(True,(False,(True,(True,(1,(2,(3,(P "foo" "foo", - (E (P "foo" "foo") (S 1.23), - D "foo" (E (P "foo" "foo") (S 1.23)) [])))))))))) +{-# OPTIONS -fglasgow-exts #-} + +module Reify (tests) where + +{- + +The following examples illustrate the reification facilities for type +structure. Most notably, we generate shallow terms using the depth of +types and constructors as means to steer the generation. + +-} + +import Test.HUnit + +import Data.Maybe +import Data.Generics +import Control.Monad.State +import CompanyDatatypes + + + +------------------------------------------------------------------------------ +-- +-- Encoding types as values; some other way. +-- +------------------------------------------------------------------------------ + +{- + +This group provides a style of encoding types as values and using +them. This style is seen as an alternative to the pragmatic style used +in Data.Typeable.typeOf and elsewhere, i.e., simply use an "undefined" +to denote a type argument. This pragmatic style suffers from lack +of robustness: one feels tempted to pattern match on undefineds. +Maybe Data.Typeable.typeOf etc. should be rewritten accordingly. + +-} + + +-- | Type as values to stipulate use of undefineds +type TypeVal a = a -> () + + +-- | The value that denotes a type +typeVal :: TypeVal a +typeVal = const () + + +-- | Test for type equivalence +sameType :: (Typeable a, Typeable b) => TypeVal a -> TypeVal b -> Bool +sameType tva tvb = typeOf (type2val tva) == + typeOf (type2val tvb) + + +-- | Map a value to its type +val2type :: a -> TypeVal a +val2type _ = typeVal + + +-- | Stipulate this idiom! +type2val :: TypeVal a -> a +type2val _ = undefined + + +-- | Constrain a type +withType :: a -> TypeVal a -> a +withType x _ = x + + +-- | The argument type of a function +argType :: (a -> b) -> TypeVal a +argType _ = typeVal + + +-- | The result type of a function +resType :: (a -> b) -> TypeVal b +resType _ = typeVal + + +-- | The parameter type of type constructor +paraType :: t a -> TypeVal a +paraType _ = typeVal + + +-- Type functions, +-- i.e., functions mapping types to values +-- +type TypeFun a r = TypeVal a -> r + + + +-- Generic type functions, +-- i.e., functions mapping types to values +-- +type GTypeFun r = forall a. Data a => TypeFun a r + + + +-- | Extend a type function +extType :: (Data a, Typeable r) => GTypeFun r -> TypeFun a r -> GTypeFun r +extType f x = maybe f id (cast x) + + + +------------------------------------------------------------------------------ +-- +-- Mapping operators to map over type structure +-- +------------------------------------------------------------------------------ + + +-- | Query all constructors of a given type + +gmapType :: ([(Constr,r')] -> r) + -> GTypeFun (Constr -> r') + -> GTypeFun r + +gmapType (o::[(Constr,r')] -> r) f (t::TypeVal a) + = + o $ zip cons query + + where + + -- All constructors of the given type + cons :: [Constr] + cons = if isAlgType $ dataTypeOf $ type2val t + then dataTypeConstrs $ dataTypeOf $ type2val t + else [] + + -- Query constructors + query :: [r'] + query = map (f t) cons + + +-- | Query all subterm types of a given constructor + +gmapConstr :: ([r] -> r') + -> GTypeFun r + -> GTypeFun (Constr -> r') + +gmapConstr (o::[r] -> r') f (t::TypeVal a) c + = + o $ query + + where + + -- Term for the given constructor + term :: a + term = fromConstr c + + -- Query subterm types + query :: [r] + query = gmapQ (f . val2type) term + + +-- | Compute arity of a given constructor +constrArity :: GTypeFun (Constr -> Int) +constrArity t c = glength $ withType (fromConstr c) t + + +-- | Query all immediate subterm types of a given type +gmapSubtermTypes :: (Data a, Typeable r) + => (r -> r -> r) -> r -> GTypeFun r -> TypeVal a -> r +gmapSubtermTypes o (r::r) f (t::TypeVal a) + = + reduce (concat (map (gmapQ (query . val2type)) terms)) + (GTypeFun' f) + + where + + -- All constructors of the given type + cons :: [Constr] + cons = if isAlgType $ dataTypeOf $ type2val t + then dataTypeConstrs $ dataTypeOf $ type2val t + else [] + + -- Terms for all constructors + terms :: [a] + terms = map fromConstr cons + + -- Query a subterm type + query :: Data b => TypeVal b -> GTypeFun' r -> (r,GTypeFun' r) + query t f = (unGTypeFun' f t, GTypeFun' (disable t (unGTypeFun' f))) + + -- Constant out given type + disable :: Data b => TypeVal b -> GTypeFun r -> GTypeFun r + disable (t::TypeVal b) f = f `extType` \(_::TypeVal b) -> r + + -- Reduce all subterm types + reduce :: [GTypeFun' r -> (r,GTypeFun' r)] -> GTypeFun' r -> r + reduce [] _ = r + reduce (xy:z) g = fst (xy g) `o` reduce z (snd (xy g)) + + +-- First-class polymorphic variation on GTypeFun +newtype GTypeFun' r = GTypeFun' (GTypeFun r) +unGTypeFun' (GTypeFun' f) = f + + +-- | Query all immediate subterm types. +-- There is an extra argument to \"constant out\" the type at hand. +-- This can be used to avoid cycles. + +gmapSubtermTypesConst :: (Data a, Typeable r) + => (r -> r -> r) + -> r + -> GTypeFun r + -> TypeVal a + -> r +gmapSubtermTypesConst o (r::r) f (t::TypeVal a) + = + gmapSubtermTypes o r f' t + where + f' :: GTypeFun r + f' = f `extType` \(_::TypeVal a) -> r + + +-- Count all distinct subterm types +gcountSubtermTypes :: Data a => TypeVal a -> Int +gcountSubtermTypes = gmapSubtermTypes (+) (0::Int) (const 1) + + +-- | A simplied variation on gmapSubtermTypes. +-- Weakness: no awareness of doubles. +-- Strength: easy to comprehend as it uses gmapType and gmapConstr. + +_gmapSubtermTypes :: (Data a, Typeable r) + => (r -> r -> r) -> r -> GTypeFun r -> TypeVal a -> r +_gmapSubtermTypes o (r::r) f + = + gmapType otype (gmapConstr oconstr f) + + where + + otype :: [(Constr,r)] -> r + otype = foldr (\x y -> snd x `o` y) r + + oconstr :: [r] -> r + oconstr = foldr o r + + +------------------------------------------------------------------------------ +-- +-- Some reifying relations on types +-- +------------------------------------------------------------------------------ + + +-- | Reachability relation on types, i.e., +-- test if nodes of type @a@ are reachable from nodes of type @b@. +-- The relation is defined to be reflexive. + +reachableType :: (Data a, Data b) => TypeVal a -> TypeVal b -> Bool +reachableType (a::TypeVal a) (b::TypeVal b) + = + or [ sameType a b + , gmapSubtermTypesConst (\x y -> or [x,y]) False (reachableType a) b + ] + + +-- | Depth of a datatype as the constructor with the minimum depth. +-- The outermost 'Nothing' denotes a type without constructors. +-- The innermost 'Nothing' denotes potentially infinite. + +depthOfType :: GTypeFun Bool -> GTypeFun (Maybe (Constr, Maybe Int)) +depthOfType p (t::TypeVal a) + = + gmapType o f t + + where + + o :: [(Constr, Maybe Int)] -> Maybe (Constr, Maybe Int) + o l = if null l then Nothing else Just (foldr1 min' l) + + f :: GTypeFun (Constr -> Maybe Int) + f = depthOfConstr p' + + -- Specific minimum operator + min' :: (Constr, Maybe Int) -> (Constr, Maybe Int) -> (Constr, Maybe Int) + min' x (_, Nothing) = x + min' (_, Nothing) x = x + min' (c, Just i) (c', Just i') | i <= i' = (c, Just i) + min' (c, Just i) (c', Just i') = (c', Just i') + + -- Updated predicate for unblocked types + p' :: GTypeFun Bool + p' = p `extType` \(_::TypeVal a) -> False + + +-- | Depth of a constructor. +-- Depth is viewed as the maximum depth of all subterm types + 1. +-- 'Nothing' denotes potentially infinite. + +depthOfConstr :: GTypeFun Bool -> GTypeFun (Constr -> Maybe Int) +depthOfConstr p (t::TypeVal a) c + = + gmapConstr o f t c + + where + + o :: [Maybe Int] -> Maybe Int + o = inc' . foldr max' (Just 0) + + f :: GTypeFun (Maybe Int) + f t' = if p t' + then + case depthOfType p t' of + Nothing -> Just 0 + Just (_, x) -> x + else Nothing + + -- Specific maximum operator + max' Nothing _ = Nothing + max' _ Nothing = Nothing + max' (Just i) (Just i') | i >= i' = Just i + max' (Just i) (Just i') = Just i' + + -- Specific increment operator + inc' Nothing = Nothing + inc' (Just i) = Just (i+1) + + +------------------------------------------------------------------------------ +-- +-- Build a shallow term +-- +------------------------------------------------------------------------------ + +shallowTerm :: (forall a. Data a => Maybe a) -> (forall b. Data b => b) +shallowTerm cust + = result + where + result :: forall b. Data b => b + -- Need a type signature here to bring 'b' into scope + result = maybe gdefault id cust + where + + -- The worker, also used for type disambiguation + gdefault :: b + gdefault = case con of + Just (con, Just _) -> fromConstrB (shallowTerm cust) con + _ -> error "no shallow term!" + + -- The type to be constructed + typeVal :: TypeVal b + typeVal = val2type gdefault + + -- The most shallow constructor if any + con :: Maybe (Constr, Maybe Int) + con = depthOfType (const True) typeVal + + + +-- For testing shallowTerm +shallowTermBase :: GenericR Maybe +shallowTermBase = Nothing + `extR` Just (1.23::Float) + `extR` Just ("foo"::String) + + + +-- Sample datatypes +data T1 = T1a deriving (Typeable, Data) -- just a constant +data T2 = T2 T1 deriving (Typeable, Data) -- little detour +data T3 = T3a T3 | T3b T2 deriving (Typeable, Data) -- recursive case +data T4 = T4 T3 T3 deriving (Typeable, Data) -- sum matters + + + +-- Sample type arguments +t0 = typeVal :: TypeVal Int +t1 = typeVal :: TypeVal T1 +t2 = typeVal :: TypeVal T2 +t3 = typeVal :: TypeVal T3 +t4 = typeVal :: TypeVal T4 +tCompany = typeVal :: TypeVal Company +tPerson = typeVal :: TypeVal Person +tEmployee = typeVal :: TypeVal Employee +tDept = typeVal :: TypeVal Dept + + + +-- Test cases +test0 = t1 `reachableType` t1 -- True +test1 = t1 `reachableType` t2 -- True +test2 = t2 `reachableType` t1 -- False +test3 = t1 `reachableType` t3 +test4 = tPerson `reachableType` tCompany +test5 = gcountSubtermTypes tPerson +test6 = gcountSubtermTypes tEmployee +test7 = gcountSubtermTypes tDept +test8 = shallowTerm shallowTermBase :: Person +test9 = shallowTerm shallowTermBase :: Employee +test10 = shallowTerm shallowTermBase :: Dept + + + +tests = ( test0 + , ( test1 + , ( test2 + , ( test3 + , ( test4 + , ( test5 + , ( test6 + , ( test7 + , ( test8 + , ( test9 + , ( test10 + ))))))))))) ~=? output + +output = (True,(True,(False,(True,(True,(1,(2,(3,(P "foo" "foo", + (E (P "foo" "foo") (S 1.23), + D "foo" (E (P "foo" "foo") (S 1.23)) [])))))))))) diff --git a/tests/Typecase1.hs b/tests/Typecase1.hs --- a/tests/Typecase1.hs +++ b/tests/Typecase1.hs @@ -1,59 +1,59 @@ -{-# OPTIONS -fglasgow-exts #-} - -module Typecase1 (tests) where - -{- - -This test demonstrates type case as it lives in Data.Typeable. -We define a function f that converts typeables into strings in some way. -Note: we only need Data.Typeable. Say: Dynamics are NOT involved. - --} - -import Test.HUnit - -import Data.Typeable -import Data.Maybe - --- Some datatype. -data MyTypeable = MyCons String deriving (Show, Typeable) - --- --- Some function that performs type case. --- -f :: (Show a, Typeable a) => a -> String -f a = (maybe (maybe (maybe others - mytys (cast a) ) - float (cast a) ) - int (cast a) ) - - where - - -- do something with ints - int :: Int -> String - int a = "got an int, incremented: " ++ show (a + 1) - - -- do something with floats - float :: Float -> String - float a = "got a float, multiplied by .42: " ++ show (a * 0.42) - - -- do something with my typeables - mytys :: MyTypeable -> String - mytys a = "got a term: " ++ show a - - -- do something with all other typeables - others = "got something else: " ++ show a - - --- --- Test the type case --- -tests = ( f (41::Int) - , f (88::Float) - , f (MyCons "42") - , f True) ~=? output - -output = ( "got an int, incremented: 42" - , "got a float, multiplied by .42: 36.96" - , "got a term: MyCons \"42\"" +{-# OPTIONS -fglasgow-exts #-} + +module Typecase1 (tests) where + +{- + +This test demonstrates type case as it lives in Data.Typeable. +We define a function f that converts typeables into strings in some way. +Note: we only need Data.Typeable. Say: Dynamics are NOT involved. + +-} + +import Test.HUnit + +import Data.Typeable +import Data.Maybe + +-- Some datatype. +data MyTypeable = MyCons String deriving (Show, Typeable) + +-- +-- Some function that performs type case. +-- +f :: (Show a, Typeable a) => a -> String +f a = (maybe (maybe (maybe others + mytys (cast a) ) + float (cast a) ) + int (cast a) ) + + where + + -- do something with ints + int :: Int -> String + int a = "got an int, incremented: " ++ show (a + 1) + + -- do something with floats + float :: Float -> String + float a = "got a float, multiplied by .42: " ++ show (a * 0.42) + + -- do something with my typeables + mytys :: MyTypeable -> String + mytys a = "got a term: " ++ show a + + -- do something with all other typeables + others = "got something else: " ++ show a + + +-- +-- Test the type case +-- +tests = ( f (41::Int) + , f (88::Float) + , f (MyCons "42") + , f True) ~=? output + +output = ( "got an int, incremented: 42" + , "got a float, multiplied by .42: 36.96" + , "got a term: MyCons \"42\"" , "got something else: True") diff --git a/tests/Typecase2.hs b/tests/Typecase2.hs --- a/tests/Typecase2.hs +++ b/tests/Typecase2.hs @@ -1,61 +1,61 @@ -{-# OPTIONS -fglasgow-exts #-} - -module Typecase2 (tests) where - -{- - -This test provides a variation on typecase1.hs. -This time, we use generic show as defined for all instances of Data. -Thereby, we get rid of the Show constraint in our functions. -So we only keep a single constraint: the one for class Data. - --} - -import Test.HUnit - -import Data.Generics -import Data.Maybe - --- Some datatype. -data MyData = MyCons String deriving (Typeable, Data) - --- --- Some function that performs type case. --- -f :: Data a => a -> String -f a = (maybe (maybe (maybe others - mytys (cast a) ) - float (cast a) ) - int (cast a) ) - - where - - -- do something with ints - int :: Int -> String - int a = "got an int, incremented: " ++ show (a + 1) - - -- do something with floats - float :: Float -> String - float a = "got a float, multiplied by .42: " ++ show (a * 0.42) - - -- do something with my data - mytys :: MyData -> String - mytys a = "got my data: " ++ gshow a - - -- do something with all other data - others = "got something else: " ++ gshow a - - --- --- Test the type case --- -tests = ( f (41::Int) - , f (88::Float) - , f (MyCons "42") - , f True) ~=? output - -output = ( "got an int, incremented: 42" - , "got a float, multiplied by .42: 36.96" - , "got my data: (MyCons \"42\")" - , "got something else: (True)") - +{-# OPTIONS -fglasgow-exts #-} + +module Typecase2 (tests) where + +{- + +This test provides a variation on typecase1.hs. +This time, we use generic show as defined for all instances of Data. +Thereby, we get rid of the Show constraint in our functions. +So we only keep a single constraint: the one for class Data. + +-} + +import Test.HUnit + +import Data.Generics +import Data.Maybe + +-- Some datatype. +data MyData = MyCons String deriving (Typeable, Data) + +-- +-- Some function that performs type case. +-- +f :: Data a => a -> String +f a = (maybe (maybe (maybe others + mytys (cast a) ) + float (cast a) ) + int (cast a) ) + + where + + -- do something with ints + int :: Int -> String + int a = "got an int, incremented: " ++ show (a + 1) + + -- do something with floats + float :: Float -> String + float a = "got a float, multiplied by .42: " ++ show (a * 0.42) + + -- do something with my data + mytys :: MyData -> String + mytys a = "got my data: " ++ gshow a + + -- do something with all other data + others = "got something else: " ++ gshow a + + +-- +-- Test the type case +-- +tests = ( f (41::Int) + , f (88::Float) + , f (MyCons "42") + , f True) ~=? output + +output = ( "got an int, incremented: 42" + , "got a float, multiplied by .42: 36.96" + , "got my data: (MyCons \"42\")" + , "got something else: (True)") + diff --git a/tests/XML.hs b/tests/XML.hs --- a/tests/XML.hs +++ b/tests/XML.hs @@ -1,195 +1,207 @@ -{-# OPTIONS -fglasgow-exts #-} - -module XML (tests) where - -{- - -This example illustrates XMLish services -to trealise (say, "serialise") heterogenous -Haskell data as homogeneous tree structures -(say, XMLish elements) and vice versa. - --} - -import Test.HUnit - -import Control.Monad -import Data.Maybe -import Data.Generics -import CompanyDatatypes - - --- HaXml-like types for XML elements -data Element = Elem Name [Attribute] [Content] - deriving (Show, Eq, Typeable, Data) - -data Content = CElem Element - | CString Bool CharData - -- ^ bool is whether whitespace is significant - | CRef Reference - | CMisc Misc - deriving (Show, Eq, Typeable, Data) - -type CharData = String - - --- In this simple example we disable some parts of XML -type Attribute = () -type Reference = () -type Misc = () - - --- Trealisation -data2content :: Data a => a -> [Content] -data2content = element - `ext1Q` list - `extQ` string - `extQ` float - - where - - -- Handle an element - element x = [CElem (Elem (tyconUQname (dataTypeName (dataTypeOf x))) - [] -- no attributes - (concat (gmapQ data2content x)))] - - -- A special case for lists - list :: Data a => [a] -> [Content] - list = concat . map data2content - - -- A special case for strings - string :: String -> [Content] - string x = [CString True x] - - -- A special case for floats - float :: Float -> [Content] - float x = [CString True (show x)] - - --- De-trealisation -content2data :: forall a. Data a => ReadX a -content2data = result - - where - - -- Case-discriminating worker - result = element - `ext1R` list - `extR` string - `extR` float - - - -- Determine type of data to be constructed - myType = myTypeOf result - where - myTypeOf :: forall a. ReadX a -> a - myTypeOf = undefined - - -- Handle an element - element = do c <- readX - case c of - (CElem (Elem x as cs)) - | as == [] -- no attributes - && x == (tyconUQname (dataTypeName (dataTypeOf myType))) - -> alts cs - _ -> mzero - - - -- A special case for lists - list :: forall a. Data a => ReadX [a] - list = ( do h <- content2data - t <- list - return (h:t) ) - `mplus` return [] - - -- Fold over all alternatives, say constructors - alts cs = foldr (mplus . recurse cs) mzero shapes - - -- Possible top-level shapes - shapes = map fromConstr consOf - - -- Retrieve all constructors of the requested type - consOf = dataTypeConstrs - $ dataTypeOf - $ myType - - -- Recurse into subterms - recurse cs x = maybe mzero - return - (runReadX (gmapM (const content2data) x) cs) - - -- A special case for strings - string :: ReadX String - string = do c <- readX - case c of - (CString _ x) -> return x - _ -> mzero - - -- A special case for floats - float :: ReadX Float - float = do c <- readX - case c of - (CString _ x) -> return (read x) - _ -> mzero - - - ------------------------------------------------------------------------------ --- --- An XML-hungry parser-like monad --- ------------------------------------------------------------------------------ - --- Type constructor -newtype ReadX a = - ReadX { unReadX :: [Content] - -> Maybe ([Content], a) } - --- Run a computation -runReadX x y = case unReadX x y of - Just ([],y) -> Just y - _ -> Nothing - --- Read one content particle -readX :: ReadX Content -readX = ReadX (\x -> if null x - then Nothing - else Just (tail x, head x) - ) - --- ReadX is a monad! -instance Monad ReadX where - return x = ReadX (\y -> Just (y,x)) - c >>= f = ReadX (\x -> case unReadX c x of - Nothing -> Nothing - Just (x', a) -> unReadX (f a) x' - ) - --- ReadX also accommodates mzero and mplus! -instance MonadPlus ReadX where - mzero = ReadX (const Nothing) - f `mplus` g = ReadX (\x -> case unReadX f x of - Nothing -> unReadX g x - y -> y - ) - - - ------------------------------------------------------------------------------ --- --- Main function for testing --- ------------------------------------------------------------------------------ - -tests = ( genCom - , ( data2content genCom - , ( zigzag person1 :: Maybe Person - , ( zigzag genCom :: Maybe Company - , ( zigzag genCom == Just genCom - ))))) ~=? output - where - -- Trealise back and forth - zigzag :: Data a => a -> Maybe a - zigzag = runReadX content2data . data2content - -output = (C [D "Research" (E (P "Laemmel" "Amsterdam") (S 8000.0)) [PU (E (P "Joost" "Amsterdam") (S 1000.0)),PU (E (P "Marlow" "Cambridge") (S 2000.0))],D "Strategy" (E (P "Blair" "London") (S 100000.0)) []],([CElem (Elem "Company" [] [CElem (Elem "Dept" [] [CString True "Research",CElem (Elem "Employee" [] [CElem (Elem "Person" [] [CString True "Laemmel",CString True "Amsterdam"]),CElem (Elem "Salary" [] [CString True "8000.0"])]),CElem (Elem "Unit" [] [CElem (Elem "Employee" [] [CElem (Elem "Person" [] [CString True "Joost",CString True "Amsterdam"]),CElem (Elem "Salary" [] [CString True "1000.0"])])]),CElem (Elem "Unit" [] [CElem (Elem "Employee" [] [CElem (Elem "Person" [] [CString True "Marlow",CString True "Cambridge"]),CElem (Elem "Salary" [] [CString True "2000.0"])])])]),CElem (Elem "Dept" [] [CString True "Strategy",CElem (Elem "Employee" [] [CElem (Elem "Person" [] [CString True "Blair",CString True "London"]),CElem (Elem "Salary" [] [CString True "100000.0"])])])])],(Just (P "Lazy" "Home"),(Just (C [D "Research" (E (P "Laemmel" "Amsterdam") (S 8000.0)) [PU (E (P "Joost" "Amsterdam") (S 1000.0)),PU (E (P "Marlow" "Cambridge") (S 2000.0))],D "Strategy" (E (P "Blair" "London") (S 100000.0)) []]),True)))) +{-# OPTIONS -fglasgow-exts #-} + +module XML (tests) where + +{- + +This example illustrates XMLish services +to trealise (say, "serialise") heterogenous +Haskell data as homogeneous tree structures +(say, XMLish elements) and vice versa. + +-} + +import Test.HUnit + +import Control.Applicative (Alternative(..), Applicative(..)) +import Control.Monad +import Data.Maybe +import Data.Generics +import CompanyDatatypes + + +-- HaXml-like types for XML elements +data Element = Elem Name [Attribute] [Content] + deriving (Show, Eq, Typeable, Data) + +data Content = CElem Element + | CString Bool CharData + -- ^ bool is whether whitespace is significant + | CRef Reference + | CMisc Misc + deriving (Show, Eq, Typeable, Data) + +type CharData = String + + +-- In this simple example we disable some parts of XML +type Attribute = () +type Reference = () +type Misc = () + + +-- Trealisation +data2content :: Data a => a -> [Content] +data2content = element + `ext1Q` list + `extQ` string + `extQ` float + + where + + -- Handle an element + element x = [CElem (Elem (tyconUQname (dataTypeName (dataTypeOf x))) + [] -- no attributes + (concat (gmapQ data2content x)))] + + -- A special case for lists + list :: Data a => [a] -> [Content] + list = concat . map data2content + + -- A special case for strings + string :: String -> [Content] + string x = [CString True x] + + -- A special case for floats + float :: Float -> [Content] + float x = [CString True (show x)] + + +-- De-trealisation +content2data :: forall a. Data a => ReadX a +content2data = result + + where + + -- Case-discriminating worker + result = element + `ext1R` list + `extR` string + `extR` float + + + -- Determine type of data to be constructed + myType = myTypeOf result + where + myTypeOf :: forall a. ReadX a -> a + myTypeOf = undefined + + -- Handle an element + element = do c <- readX + case c of + (CElem (Elem x as cs)) + | as == [] -- no attributes + && x == (tyconUQname (dataTypeName (dataTypeOf myType))) + -> alts cs + _ -> mzero + + + -- A special case for lists + list :: forall a. Data a => ReadX [a] + list = ( do h <- content2data + t <- list + return (h:t) ) + `mplus` return [] + + -- Fold over all alternatives, say constructors + alts cs = foldr (mplus . recurse cs) mzero shapes + + -- Possible top-level shapes + shapes = map fromConstr consOf + + -- Retrieve all constructors of the requested type + consOf = dataTypeConstrs + $ dataTypeOf + $ myType + + -- Recurse into subterms + recurse cs x = maybe mzero + return + (runReadX (gmapM (const content2data) x) cs) + + -- A special case for strings + string :: ReadX String + string = do c <- readX + case c of + (CString _ x) -> return x + _ -> mzero + + -- A special case for floats + float :: ReadX Float + float = do c <- readX + case c of + (CString _ x) -> return (read x) + _ -> mzero + + + +----------------------------------------------------------------------------- +-- +-- An XML-hungry parser-like monad +-- +----------------------------------------------------------------------------- + +-- Type constructor +newtype ReadX a = + ReadX { unReadX :: [Content] + -> Maybe ([Content], a) } + +-- Run a computation +runReadX x y = case unReadX x y of + Just ([],y) -> Just y + _ -> Nothing + +-- Read one content particle +readX :: ReadX Content +readX = ReadX (\x -> if null x + then Nothing + else Just (tail x, head x) + ) + +instance Functor ReadX where + fmap = liftM + +instance Applicative ReadX where + pure = return + (<*>) = ap + +instance Alternative ReadX where + (<|>) = mplus + empty = mzero + +-- ReadX is a monad! +instance Monad ReadX where + return x = ReadX (\y -> Just (y,x)) + c >>= f = ReadX (\x -> case unReadX c x of + Nothing -> Nothing + Just (x', a) -> unReadX (f a) x' + ) + +-- ReadX also accommodates mzero and mplus! +instance MonadPlus ReadX where + mzero = ReadX (const Nothing) + f `mplus` g = ReadX (\x -> case unReadX f x of + Nothing -> unReadX g x + y -> y + ) + + + +----------------------------------------------------------------------------- +-- +-- Main function for testing +-- +----------------------------------------------------------------------------- + +tests = ( genCom + , ( data2content genCom + , ( zigzag person1 :: Maybe Person + , ( zigzag genCom :: Maybe Company + , ( zigzag genCom == Just genCom + ))))) ~=? output + where + -- Trealise back and forth + zigzag :: Data a => a -> Maybe a + zigzag = runReadX content2data . data2content + +output = (C [D "Research" (E (P "Laemmel" "Amsterdam") (S 8000.0)) [PU (E (P "Joost" "Amsterdam") (S 1000.0)),PU (E (P "Marlow" "Cambridge") (S 2000.0))],D "Strategy" (E (P "Blair" "London") (S 100000.0)) []],([CElem (Elem "Company" [] [CElem (Elem "Dept" [] [CString True "Research",CElem (Elem "Employee" [] [CElem (Elem "Person" [] [CString True "Laemmel",CString True "Amsterdam"]),CElem (Elem "Salary" [] [CString True "8000.0"])]),CElem (Elem "Unit" [] [CElem (Elem "Employee" [] [CElem (Elem "Person" [] [CString True "Joost",CString True "Amsterdam"]),CElem (Elem "Salary" [] [CString True "1000.0"])])]),CElem (Elem "Unit" [] [CElem (Elem "Employee" [] [CElem (Elem "Person" [] [CString True "Marlow",CString True "Cambridge"]),CElem (Elem "Salary" [] [CString True "2000.0"])])])]),CElem (Elem "Dept" [] [CString True "Strategy",CElem (Elem "Employee" [] [CElem (Elem "Person" [] [CString True "Blair",CString True "London"]),CElem (Elem "Salary" [] [CString True "100000.0"])])])])],(Just (P "Lazy" "Home"),(Just (C [D "Research" (E (P "Laemmel" "Amsterdam") (S 8000.0)) [PU (E (P "Joost" "Amsterdam") (S 1000.0)),PU (E (P "Marlow" "Cambridge") (S 2000.0))],D "Strategy" (E (P "Blair" "London") (S 100000.0)) []]),True))))