October 2006 - Haskell-Cafe

hsffig output produces errors from hsc2hs
by Soenke Hahn 07 Oct '06

07 Oct '06

Hi! I want to interface to JACK (http://jackaudio.org/) from a haskell programm and i tried to process jack/jack.h (the JACK API) with hsffig and its output with hsc2hs. I get several error messages from hsc2hs like this: JACK.hsc:198: error: syntax error before ‘}’ token JACK.hsc:198: error: void value not ignored as it ought to be The line in JACK.hsc: c_PTHREAD_COND_INITIALIZER = #const PTHREAD_COND_INITIALIZER The commands i used: gcc -E -dD /usr/include/jack/jack.h | hsffig | tee JACK.hsc hsc2hs -t template-hsffig.h JACK.hsc -I /usr/share/doc/hsffig i tried both version 0.1.2-2 from my distribution (ubuntu) and version 1.0 from the homepage. What am i doing wrong? Did i miss something essential? Soenke

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OOHaskell problems
by Jason Dagit 07 Oct '06

07 Oct '06

Hello, I wanted to try using OOHaskell as a library, but I've run into some problems I don't understand. I downloaded the copy from: http://homepages.cwi.nl/~ralf/OOHaskell/ In the HList subdirectory I created a .cabal file which exposes as many of the modules in HList as I could. I then installed the HList library using cabal. Back in the main OOHaskell directory I created a .cabal file for OOHaskell which depended on the newly installed HList library. The OOHaskell library exposes the modules: DeepNarrow New Nominal OOHaskell After I installed the OOHaskell library I ran: ghc --make -package OOHaskell -package HList SimpleIO.hs Chasing modules from: SimpleIO.hs Compiling Nominal ( ./Nominal.hs, ./Nominal.o ) Compiling New ( ./New.hs, ./New.o ) Compiling DeepNarrow ( ./DeepNarrow.hs, ./DeepNarrow.o ) Compiling OOHaskell ( ./OOHaskell.hs, ./OOHaskell.o ) Compiling SimpleIO ( SimpleIO.hs, SimpleIO.o ) SimpleIO.hs:44:11: No instance for (HasField (Proxy Field1) HNil v) arising from use of `foo' at SimpleIO.hs:44:11-13 Probable fix: add an instance declaration for (HasField (Proxy Field1) HNil v) In the definition of `testfoo': testfoo = foo ((field1 .=. True) .*. emptyRecord) SimpleIO.hs:116:7: No instance for (HasField (Proxy MoveX) HNil (a -> IO t)) arising from use of `#' at SimpleIO.hs:116:7 Probable fix: add an instance declaration for (HasField (Proxy MoveX) HNil (a -> IO t)) In the first argument of `($)', namely `p # moveX' In a 'do' expression: (p # moveX) $ 3 In the definition of `myFirstOOP': myFirstOOP = do p <- point (p # getX) >>= System.IO.print (p # moveX) $ 3 (p # getX) >>= System.IO.print SimpleIO.hs:124:19: No instance for (HasField (Proxy MutableX) HNil (IORef a)) arising from use of `#' at SimpleIO.hs:124:19 Probable fix: add an instance declaration for (HasField (Proxy MutableX) HNil (IORef a)) In the first argument of `writeIORef', namely `(p # mutableX)' In a 'do' expression: writeIORef (p # mutableX) 42 In the definition of `mySecondOOP': mySecondOOP = do p <- point writeIORef (p # mutableX) 42 (p # getX) >>= System.IO.print SimpleIO.hs:177:23: No instance for (HasField (Proxy GetX) HNil (IO a)) arising from use of `#' at SimpleIO.hs:177:23 Probable fix: add an instance declaration for (HasField (Proxy GetX) HNil (IO a)) In the second argument of `(>>=)', namely `(# getX)' In the first argument of `(>>=)', namely `localClass >>= ((# getX))' In the result of a 'do' expression: (localClass >>= ((# getX))) >>= System.IO.print SimpleIO.hs:225:8: No instance for (HasField (Proxy GetOffset) HNil (IO a)) arising from use of `#' at SimpleIO.hs:225:8 Probable fix: add an instance declaration for (HasField (Proxy GetOffset) HNil (IO a)) In the first argument of `(>>=)', namely `p # getOffset' In the result of a 'do' expression: (p # getOffset) >>= System.IO.print In the definition of `testPara': testPara = do p <- para_point 1 (p # getX) >>= System.IO.print (p # moveX) $ 2 (p # getX) >>= System.IO.print (p # getOffset) >>= System.IO.print To investigate this further, in the OOHaskell directory I typed: $ ghci -fglasgow-exts -fallow-overlapping-instances -fallow-undecidable-instances -i./HList ShapesLub.hs ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.4.2, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base-1.0 ... linking ... done. Compiling FakePrelude ( ./HList/FakePrelude.hs, interpreted ) Compiling HListPrelude ( ./HList/HListPrelude.hs, interpreted ) Compiling GhcExperiments ( ./HList/GhcExperiments.hs, interpreted ) Compiling HArray ( ./HList/HArray.hs, interpreted ) Compiling HZip ( ./HList/HZip.hs, interpreted ) Compiling HOccurs ( ./HList/HOccurs.hs, interpreted ) Compiling HTypeIndexed ( ./HList/HTypeIndexed.hs, interpreted ) Compiling Record ( ./HList/Record.hs, interpreted ) Compiling GhcRecord ( ./HList/GhcRecord.hs, interpreted ) Compiling Label4 ( ./HList/Label4.hs, interpreted ) Compiling New ( ./New.hs, interpreted ) Compiling TIP ( ./HList/TIP.hs, interpreted ) Compiling TIC ( ./HList/TIC.hs, interpreted ) Compiling GhcSyntax ( ./HList/GhcSyntax.hs, interpreted ) Compiling TypeCastGeneric1 ( ./HList/TypeCastGeneric1.hs, interpreted ) Compiling TypeEqBoolGeneric ( ./HList/TypeEqBoolGeneric.hs, interpreted ) Compiling TypeEqGeneric1 ( ./HList/TypeEqGeneric1.hs, interpreted ) Compiling Variant ( ./HList/Variant.hs, interpreted ) Compiling Nominal ( ./Nominal.hs, interpreted ) Compiling CommonMain ( ./HList/CommonMain.hs, interpreted ) Compiling DeepNarrow ( ./DeepNarrow.hs, interpreted ) Compiling OOHaskell ( ./OOHaskell.hs, interpreted ) Compiling Shapes ( ./Shapes.hs, interpreted ) Compiling ShapesLub ( ShapesLub.hs, interpreted ) Ok, modules loaded: ShapesLub, Shapes, OOHaskell, DeepNarrow, CommonMain, Nominal, Variant, TypeEqGeneric1, TypeEqBoolGeneric, TypeCastGeneric1, GhcSyntax, TIC, TIP, New, Label4, GhcRecord, Record, HTypeIndexed, HOccurs, HZip, HArray, GhcExperiments, HListPrelude, FakePrelude. *ShapesLub> main Drawing a Rectangle at:(10,20), width 5, height 6 Drawing a Rectangle at:(110,120), width 5, height 6 Drawing a Circle at:(15,25), radius 8 Drawing a Circle at:(115,125), radius 8 Drawing a Rectangle at:(0,0), width 30, height 15 *ShapesLub> So that seemed to work, but: $ ghci -fglasgow-exts -fallow-overlapping-instances -fallow-undecidable-instances -package OOHaskell -package HList ShapesLub.hs ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.4.2, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base-1.0 ... linking ... done. Loading package HList-0.1 ... linking ... done. Loading package OOHaskell-0.1 ... linking ... done. Skipping Nominal ( ./Nominal.hs, ./Nominal.o ) Skipping New ( ./New.hs, ./New.o ) Skipping DeepNarrow ( ./DeepNarrow.hs, ./DeepNarrow.o ) Skipping OOHaskell ( ./OOHaskell.hs, ./OOHaskell.o ) Compiling Shapes ( ./Shapes.hs, interpreted ) Compiling ShapesLub ( ShapesLub.hs, interpreted ) ShapesLub.hs:30:19: No instances for (HasField (Proxy MoveTo) HNil (a5 -> a6 -> IO t5), HasField (Proxy GetY) HNil (IO a6), HasField (Proxy GetX) HNil (IO a5), HasField (Proxy SetY) HNil (t4 -> t t1), HasField (Proxy SetX) HNil (t2 -> t t3), HasField (Proxy GetWidth) HNil (IO a7), HasField (Proxy GetHeight) HNil (IO a8), HExtract HNil (Proxy Draw) (IO ())) arising from use of `rectangle' at ShapesLub.hs:30:19-27 Probable fix: add an instance declaration for (HasField (Proxy MoveTo) HNil (a5 -> a6 -> IO t5), HasField (Proxy GetY) HNil (IO a6), HasField (Proxy GetX) HNil (IO a5), HasField (Proxy SetY) HNil (t4 -> t t1), HasField (Proxy SetX) HNil (t2 -> t t3), HasField (Proxy GetWidth) HNil (IO a7), HasField (Proxy GetHeight) HNil (IO a8), HExtract HNil (Proxy Draw) (IO ())) In the first argument of `mfix', namely `(rectangle (10 :: Int) (20 :: Int) 5 6)' In a 'do' expression: s1 <- mfix (rectangle (10 :: Int) (20 :: Int) 5 6) In the definition of `main': main = do s1 <- mfix (rectangle (10 :: Int) (20 :: Int) 5 6) s2 <- mfix (circle (15 :: Int) 25 8) let scribble = ... mapM_ (\ shape -> ...) scribble arec <- mfix (rectangle (0 :: Int) (0 :: Int) 15 15) (arec # setWidth) $ 30 arec # draw ShapesLub.hs:31:19: No instance for (HasField (Proxy GetRadius) HNil (IO a6)) arising from use of `circle' at ShapesLub.hs:31:19-24 Probable fix: add an instance declaration for (HasField (Proxy GetRadius) HNil (IO a6)) In the first argument of `mfix', namely `(circle (15 :: Int) 25 8)' In a 'do' expression: s2 <- mfix (circle (15 :: Int) 25 8) In the definition of `main': main = do s1 <- mfix (rectangle (10 :: Int) (20 :: Int) 5 6) s2 <- mfix (circle (15 :: Int) 25 8) let scribble = ... mapM_ (\ shape -> ...) scribble arec <- mfix (rectangle (0 :: Int) (0 :: Int) 15 15) (arec # setWidth) $ 30 arec # draw ShapesLub.hs:38:34: No instance for (HasField (Proxy RMoveTo) HNil (t -> t1 -> IO t2)) arising from use of `#' at ShapesLub.hs:38:34 Probable fix: add an instance declaration for (HasField (Proxy RMoveTo) HNil (t -> t1 -> IO t2)) In a 'do' expression: (shape # rMoveTo) 100 100 In a lambda abstraction: \ shape -> do shape # draw (shape # rMoveTo) 100 100 shape # draw In the first argument of `mapM_', namely `(\ shape -> do shape # draw (shape # rMoveTo) 100 100 shape # draw)' ShapesLub.hs:44:12: No instance for (HasField (Proxy SetWidth) HNil (a -> IO t)) arising from use of `#' at ShapesLub.hs:44:12 Probable fix: add an instance declaration for (HasField (Proxy SetWidth) HNil (a -> IO t)) In the first argument of `($)', namely `arec # setWidth' In a 'do' expression: (arec # setWidth) $ 30 In the definition of `main': main = do s1 <- mfix (rectangle (10 :: Int) (20 :: Int) 5 6) s2 <- mfix (circle (15 :: Int) 25 8) let scribble = ... mapM_ (\ shape -> ...) scribble arec <- mfix (rectangle (0 :: Int) (0 :: Int) 15 15) (arec # setWidth) $ 30 arec # draw ShapesLub.hs:46:12: No instance for (HasField (Proxy Draw) HNil (IO b)) arising from use of `#' at ShapesLub.hs:46:12 Probable fix: add an instance declaration for (HasField (Proxy Draw) HNil (IO b)) In the result of a 'do' expression: arec # draw In the definition of `main': main = do s1 <- mfix (rectangle (10 :: Int) (20 :: Int) 5 6) s2 <- mfix (circle (15 :: Int) 25 8) let scribble = ... mapM_ (\ shape -> ...) scribble arec <- mfix (rectangle (0 :: Int) (0 :: Int) 15 15) (arec # setWidth) $ 30 arec # draw Failed, modules loaded: Shapes, OOHaskell, DeepNarrow, New, Nominal. *Shapes> Inspecting HasField and Proxy in the working ghci says: *ShapesLub> :i HasField class HasField l r v | l r -> v where hLookupByLabel :: l -> r -> v -- Defined at ./HList/Record.hs:140:6 instance (HasField l x v, Nomination f) => HasField l (N f x) v -- Defined at ./Nominal.hs:49:0 instance HasField l r v => HasField l (Record r) v -- Defined at ./HList/Record.hs:143:0 instance (HEq l l' b, HasField' b l (HCons (l', v') r) v) => HasField l (HCons (l', v') r) v -- Defined at ./HList/Record.hs:149:0 *ShapesLub> :i Proxy data Proxy e -- Defined at ./HList/FakePrelude.hs:218:5 instance Show (Proxy e) -- Defined at ./HList/FakePrelude.hs:219:0 instance Typeable x => Typeable (Proxy x) -- Defined at ./HList/GhcRecord.hs:229:0 instance TypeEq x y b => HEq (Proxy x) (Proxy y) b -- Defined at ./HList/Label4.hs:27:0 instance (HType2HNat e l n, HTypes2HNats ps l ns) => HTypes2HNats (HCons (Proxy e) ps) l (HCons n ns) -- Defined at ./HList/HTypeIndexed.hs:90:0 instance Typeable x => ShowLabel (Proxy x) -- Defined at ./HList/Label4.hs:32:0 instance Fail (ProxyFound x) => HasNoProxies (HCons (Proxy x) l) -- Defined at ./HList/GhcRecord.hs:73:0 instance HTypeProxied l => HTypeProxied (HCons (Proxy e) l) -- Defined at ./HList/TIC.hs:68:0 instance HMaybied l l' => HMaybied (HCons (Proxy e) l) (HCons (Maybe e) l') -- Defined at ./HList/Variant.hs:53:0 While, the ouput in the non-working ghci sessions has equivalent output: *Shapes> :i HasField class HasField l r v | l r -> v where hLookupByLabel :: l -> r -> v -- Imported from Record instance (HasField l x v, Nomination f) => HasField l (N f x) v -- Imported from Nominal instance (HEq l l' b, HasField' b l (HCons (l', v') r) v) => HasField l (HCons (l', v') r) v -- Imported from Record instance HasField l r v => HasField l (Record r) v -- Imported from Record *Shapes> :i Proxy data Proxy e -- Imported from FakePrelude instance Show (Proxy e) -- Imported from FakePrelude instance Typeable x => Typeable (Proxy x) -- Imported from GhcRecord instance TypeEq x y b => HEq (Proxy x) (Proxy y) b -- Imported from Label4 instance Typeable x => ShowLabel (Proxy x) -- Imported from Label4 instance Fail (ProxyFound x) => HasNoProxies (HCons (Proxy x) l) -- Imported from GhcRecord instance HMaybied l l' => HMaybied (HCons (Proxy e) l) (HCons (Maybe e) l') -- Imported from Variant instance HTypeProxied l => HTypeProxied (HCons (Proxy e) l) -- Imported from TIC instance (HType2HNat e l n, HTypes2HNats ps l ns) => HTypes2HNats (HCons (Proxy e) ps) l (HCons n ns) -- Imported from HTypeIndexed I'm at a loss to figure out why the OOHaskell library I created does not behave the same as building the examples next to the HList source. Thanks, Jason

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Haddock Parse Errors
by Matthew Bromberg 06 Oct '06

06 Oct '06

I am trying to use Haddock for the first time on windows for a reasonably large project. I must be completely clueless because I seem to generate a lot of parse errors that have no reasonable explanation. In some cases it seems like Haddock is white space sensitive requiring the same indentation as my source code. If so, this is not clearly documented. However consider this example: in my matrix library I have this code snippet: ... -- | class instance Rmatrix, real only matrices instance Matrix Rmatrix where -- | tells us if its a submatrix (better to use pattern matching) issub x = case x of Rindx n -> False Rsubindx n -> True ... This generates a parse error on the line -- | class instance Rmatrix, real only matrices at the first s in class. Removing the | from the comment generates a parse error on the instance declaration even though there are no haddock comments that apply to it! The code prior to this looks something like... -- | copy one matrix into another copy :: m -> m -> m copy a b = mio $ do ka <- pushsub a ... and is part of the class declaration itself. I'm not sure why an auto-documentation tool shouldn't be a bit more forgiving vis a vis it's syntax. Maybe flag errors as warnings but keep on going. I run haddock from the command prompt via the command haddock.exe -o docs -v -h matrix.hs

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Having our cake and eating it too
by Michael Shulman 05 Oct '06

05 Oct '06

This proposal is somewhat tongue in cheek, but at least it's amusing, and who knows, it might be good for something. The idea is that one could, in theory, allow both prefix unary minus and right sections of subtraction, with the type-checker deciding which is meant based on the context. Has this been noticed before? Consider the following code snippet, which runs in GHC 6.6 (with the new ability to define postfix operators). > {-# OPTIONS -fglasgow-exts -fallow-undecidable-instances -fallow-overlapping-instances #-} > module Minus where > import TypeCast > class Minus a b where > (<->) :: a -> b > instance (Num a, TypeCast a b) => Minus a b where > (<->) = typeCast . negate > instance (TypeCast a b, Num b, TypeCast b c) => Minus a (b -> c) where > (<->) x y = typeCast ((typeCast x) - y) (TypeCast is the usual one from HList etc.) Loading this in the interpreter, we now have: *Minus> (1 <->) :: Int -1 *Minus> 3 <-> 1 :: Int 2 *Minus> map (<-> 1) [2..5] [1,2,3,4] *Minus> map (1 <->) [2..5] [-1,-2,-3,-4] *Minus> map (<->) [2..5] :: [Int] [-2,-3,-4,-5] *Minus> zipWith (<->) [1,3,5] [1,2,3] [0,1,2] In short, the operator <-> can be used as *either* an infix subtraction operator (which can be sectioned on both sides) or a postfix unary negation operator (which can also be sectioned once). The trick is the same one used for variadic arguments: the type-checker can infer from context whether (1 <->) should return a number or a function, and resolves it accordingly. Thus, if we could figure out a way to define prefix operators, analogous to the way we can now define postfix operators, we could in theory allow prefix unary minus and right sections of subtraction to coexist peacefully. But I haven't had much luck coming up with a non-ugly suggestion for how to do this. I'd be interested to hear if anyone else has ideas, although I doubt any such solution would ever make it into any Haskell standard. (-: It's also unfortunate that we need the explicit type signatures in the interpreter above, but otherwise there would be no context for type-inference based on the return value. As usual, though, this problem would probably hardly ever arise in an actual program, where most values have a known type. (Actually, I still don't understand why a type signature is necessary on 3 <-> 1; anyone care to enlighten me?) Comments? Mike

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collection monads
by tpledger＠ihug.co.nz 05 Oct '06

05 Oct '06

Matthias Fischmann wrote: > another beginners question about monads: given the type > > | data (Ix x) => Permutation x = Permutation [x] > > i wanted to define > > | instance Monad Permutation where > | return xs = Permutation xs > > but of course nothing about the monad class guarantees xs to be of > type list. the monad class seems unsuitable for holding collections, > and i am inclined to not instantiate permutations. > > just to be sure: is there any easy way to do it that i missed? Do you expect the contained type x to change during a sequence of monadic actions? e.g. would you ever use (>>=) at the type 'Permutation Int -> (Int -> Permutation Bool) -> Permutation Bool'? If not, you could separate each permutation into keys and values: data Permutation k v = Permutation [(k, v)] instance (Ix k) => Monad (Permutation k) Regards, Tom

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Searching all the source code of the world
by Stephane Bortzmeyer 05 Oct '06

05 Oct '06

http://www.google.com/codesearch A great tool (which fulfills a different need than Hoogle) if you are looking for a concrete example of use of such or such function. Unfortunately, "lang:haskell" is not recognized (as a workaround, "file:\.hs" is OK). This has already been reported: http://groups.google.com/group/Google-Code-Search/browse_thread/thread/8c9e…

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haskell vim / my coding aids
by Marc Weber 05 Oct '06

05 Oct '06

I've been busy for some days writing this humbled helper scripts for vim: Goto vim -> by Marc Weber http://www.haskell.org/haskellwiki/Libraries_and_tools/Program_development#… If you find it useful and drop me a line I'll be glad to read your feedback. Marc

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how to create new repository on darcs.haskell.org?
by Bulat Ziganshin 05 Oct '06

05 Oct '06

Hello haskell-cafe, i want to make my library available via darcs repository on darcs.haskell.org. how i can arrange it? if it is required, i already have user account on haskell.org server -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Mission: To take args from a list... generally
by tpledger＠ihug.co.nz 05 Oct '06

05 Oct '06

Joel Koerwer wrote: > Let's say I want to evaluate a function of type > (a->a->...->a->a), taking the arguments from a > list. If know the function ahead of time, I can > simply wrap it: > > foo a b c d = ... > wrapFoo (a:b:c:d:_) = foo a b c d > > But, as an exercise, I challenged myself to write > a function, multApply :: (a->a->...->a->a) -> [a] > -> a, that automatically does the wrapping for any > such function. This came up a while ago (but with a list of functions of different arities, all being fed one argument). I found Scott Turner's pure Haskell 98 solution very illuminating: http://www.haskell.org/pipermail/haskell-cafe/2000-November/001332.html Regards, Tom

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seeking paper: Computing with lattices: An application of type classes
by Mathew Mills 04 Oct '06

04 Oct '06

I am not sure how to go about getting a copy of this paper. http://citeseer.ist.psu.edu/context/320255/0 I was hoping someone here could give me a pointer.

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