Re: [Haskell-cafe] Basic binary IO
Ah, thanks Don, Brandon, I looked at this but neglected to read through and understand the example enough. Thanks for the tips, they're a great help. Don Stewart wrote: jamie.love: bmpHeader = runPut $ do put 'B' put 'M' put (0 :: Int32) put (0 :: Int32) put (14 :: Int32) Yields the lazy bytestring, BM\NUL\NUL\NUL\NUL\NUL\NUL\NUL\NUL\NUL\NUL\NUL\SO -- Jamie Love Senior Consultant Aviarc Australia Mobile: +61 400 548 048 This message has been scanned for viruses and dangerous content by MailScanner and is believed to be clean. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] bytea decoding
Does anyone know of a library that will handle bytea encodings from postgres? The bytea field that I need to access contains a jpg file. I want to retrieve it from the database and write it out for an image display program. bytea: Bytea octets are also escaped in the output. In general, each non-printable octet is converted into its equivalent three-digit octal value and preceded by one backslash. Most printable octets are represented by their standard representation in the client character set. The octet with decimal value 92 (backslash) has a special alternative output representation. Details are in Table 8-8http://www.postgresql.org/docs/7.4/interactive/datatype-binary.html#DATATYPE-BINARY-RESESC. *Table 8-8. bytea Output Escaped Octets* Decimal Octet ValueDescriptionEscaped Output Representation ExampleOutput Result92backslash\\SELECT '\\134'::bytea;\\ 0 to 31 and 127 to 255 non-printable octets\*xxx* (octal value) SELECT '\\001'::bytea;\00132 to 126printable octetsclient character set representation SELECT '\\176'::bytea;~ Depending on the front end to PostgreSQL you use, you may have additional work to do in terms of escaping and unescaping bytea strings. For example, you may also have to escape line feeds and carriage returns if your interface automatically translates these. So, here is part of the file from the database: \377\330\377\340\000\020JFIF\000\001\001\000\000\001\000\001\000\000\377\333\000C\000\012\007\007\010\007\006\012\010\010\010\013\012\012\013\016\030\020\016\015\015\016\035\025\026\021\030#\037%$\037!+7/)4)!0A149;%.DICH7=;\377 I may have to write a converter myself but I don't like re-inventing the wheel if I don't need to do so. Any pointers would be greatly appreciated. Bryan Green ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] bug in all about monads tutorial
Hi, About 3 weeks ago I reported this bug to Jeff Newbern. But I got no response - maybe I got filtered out as spam :) Since it was not fixed I'm trying once more here. Maybe there is somebody here who has access to the web site http://www.haskell.org/all_about_monads and cares enough to fix it. On page http://www.haskell.org/all_about_monads/html/writermonad.html there is listens defined like this: listens f m = do (a,w) - m; return (a,f w) ... but it should be like this: listens f m = do (a,w) - listen m; return (a,f w) ... or maybe a less strict option (as ghc libs have it): listens f m = do ~(a,w) - listen m; return (a,f w) Peter. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Need help with Parsec
Hi, I'm playing since a few hours with Parsec and trying to write a small html (fragment) parser, but I'm stuck in a point which I really can't understand. The problem seem to be either in parseProperCont or in closing (see code below). It looks like closing does not work (but it is a very simple function!) or (also hard to believe) function try from Parsec has some problems. Anyway I get this answer: Prelude ParseSHtml pf parseHtmlFrg ptest.txt Left ptest.txt (line 5, column 2): unexpected / expecting element name when I'm parsing this file: div id=normtext one line with breakbr / another line br /br / Mail: a href=mailto:[EMAIL PROTECTED][EMAIL PROTECTED]/a /div with this code (sorry for the longer mail): import Text.ParserCombinators.Parsec hiding (label) import Text.XHtml.Strict -- Helper function: parse a string up to one of the given chars upTo :: [Char] - Parser [Char] upTo ds = many1 (noneOf ds) parseHtmlFrg :: Parser Html parseHtmlFrg = do many space choice [parseElem, parseText] ? html fragment parseElem :: Parser Html parseElem = do en - parseElTag many1 space (ats, cnt) - restElem en return $ compElem en cnt ! ats ? html element -- Compose a html element from tag name and content compElem en cnt = if isNoHtml cnt then itag en else tag en cnt parseElTag :: Parser String parseElTag = do char '' en - elemName return en ? element tag elemName :: Parser String elemName = many1 lower ? element name restElem :: String - Parser ([HtmlAttr], Html) restElem nm = do ats - parseAttList ht - (restElNoCont | restElCont nm) return (ats, ht) ? ( or / to close the tag ++ nm) -- Rest element with no content restElNoCont = do char '/' char '' return noHtml ? / -- Rest element with content restElCont nm = do char '' many space els - parseProperCont nm return $ concatHtml els ? element with content -- Parse closing tag or proper content(s) parseProperCont :: String - Parser [Html] parseProperCont nm = try (do closing nm return [] ) | (do h - parseHtmlFrg hs - parseProperCont nm return (h:hs) ) -- | return [] ? proper element content closing nm = do char '' char '/' nm1 - elemName char '' if nm1 == nm then return () else fail $ nm ++ , encountered ++ nm1 ? (closing of ++ nm) -- Parse a html attribute parseAttr :: Parser HtmlAttr parseAttr = do at - many1 lower char '=' va - parseQuote many space return $ strAttr at va ? Attribut parseAttList = many1 parseAttr | return [] ? attribute list -- Parse a quoted string parseQuote :: Parser String parseQuote = do char '' cs - upTo [''] char '' return cs -- Parse a text element parseText :: Parser Html parseText = do s - upTo return (stringToHtml s) ? some text -- For tests: pf p file = parseFromFile p file Nicu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Type issues for a foldable trie in Haskell
Hello there,
I have written a trie in Haskell generalized to Eq a = [a] rather than
simply String. I want to make this type an instance of Foldable, but I've
run into a type dilemma. My datatypes look like this:
data TrieElem a = Elem a | Start | End
deriving (Read, Show, Eq, Ord)
data Trie a = Trie {label :: TrieElem a
,children :: [Trie a]}
deriving (Read, Show, Eq, Ord)
The signature of Data.Foldable.foldr is (Data.Foldable.Foldable t) = (a
- b - b) - b - t a - b. However, I want the functions in Foldable to
operate on the _list type_ that Trie stores rather than the _elements_ of
that list type---Trie a stores lists of type a. For example, a Trie
storing strings would have type Trie Char, and I want Trie Char to be
Foldable, but where the functions operate on String rather than Char.
So, with the datatype definitions of Trie and TrieElem as they are above,
to define a fold function that operates the way I want would have
signature ([a] - b - b) - b - Trie a - b, which is no good for making
Trie a an instance of Foldable.
Hopefully this doesn't just seem like rambling :-). How might I rewrite
my datatypes to do what I want, preferably without using ghc extensions?
Thanks!
Brad Larsen
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Re: [Haskell-cafe] Need help with Parsec
Here's a handy simple function I've found very useful. You'll obviously also need to import Debug.Trace: pTrace s = pt | return () where pt = try $ do x - try $ many1 anyChar trace (s++: ++x) $ try $ char 'z' fail x It could perhaps be cleaner, but it does the job for me fine. Just insert a line like pTrace label anywhere in your parsing functions and whenever parsec hits that line you get a nice line of output: label: rest of string to be parsed This tends to help track down just where your code goes wrong. Try works like it should in my experience, but that doesn't necessarily mean it works how you expect. Regards, s On Jan 20, 2008, at 12:12 PM, Nicu Ionita wrote: Hi, I'm playing since a few hours with Parsec and trying to write a small html (fragment) parser, but I'm stuck in a point which I really can't understand. The problem seem to be either in parseProperCont or in closing (see code below). It looks like closing does not work (but it is a very simple function!) or (also hard to believe) function try from Parsec has some problems. Anyway I get this answer: Prelude ParseSHtml pf parseHtmlFrg ptest.txt Left ptest.txt (line 5, column 2): unexpected / expecting element name when I'm parsing this file: div id=normtext one line with breakbr / another line br /br / Mail: a href=mailto:[EMAIL PROTECTED][EMAIL PROTECTED]/a /div with this code (sorry for the longer mail): import Text.ParserCombinators.Parsec hiding (label) import Text.XHtml.Strict -- Helper function: parse a string up to one of the given chars upTo :: [Char] - Parser [Char] upTo ds = many1 (noneOf ds) parseHtmlFrg :: Parser Html parseHtmlFrg = do many space choice [parseElem, parseText] ? html fragment parseElem :: Parser Html parseElem = do en - parseElTag many1 space (ats, cnt) - restElem en return $ compElem en cnt ! ats ? html element -- Compose a html element from tag name and content compElem en cnt = if isNoHtml cnt then itag en else tag en cnt parseElTag :: Parser String parseElTag = do char '' en - elemName return en ? element tag elemName :: Parser String elemName = many1 lower ? element name restElem :: String - Parser ([HtmlAttr], Html) restElem nm = do ats - parseAttList ht - (restElNoCont | restElCont nm) return (ats, ht) ? ( or / to close the tag ++ nm) -- Rest element with no content restElNoCont = do char '/' char '' return noHtml ? / -- Rest element with content restElCont nm = do char '' many space els - parseProperCont nm return $ concatHtml els ? element with content -- Parse closing tag or proper content(s) parseProperCont :: String - Parser [Html] parseProperCont nm = try (do closing nm return [] ) | (do h - parseHtmlFrg hs - parseProperCont nm return (h:hs) ) -- | return [] ? proper element content closing nm = do char '' char '/' nm1 - elemName char '' if nm1 == nm then return () else fail $ nm ++ , encountered ++ nm1 ? (closing of ++ nm) -- Parse a html attribute parseAttr :: Parser HtmlAttr parseAttr = do at - many1 lower char '=' va - parseQuote many space return $ strAttr at va ? Attribut parseAttList = many1 parseAttr | return [] ? attribute list -- Parse a quoted string parseQuote :: Parser String parseQuote = do char '' cs - upTo [''] char '' return cs -- Parse a text element parseText :: Parser Html parseText = do s - upTo return (stringToHtml s) ? some text -- For tests: pf p file = parseFromFile p file Nicu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hangman game
Ronald Guida wrote: Hi, I'm interested in learning how to program games. Since I have to start somewhere, I decided to write a simple Hangman game. I'm wondering if anyone can look at my code and give me some feedback. Nicely written. The design reads very much like a straight translation from the imperative style, which is why so much of it is in the IO monad. There is nothing wrong with this for a simple game like Hangman, but for larger games it doesn't scale. So here are a few pointers to ways of rewriting it to keep the IO to the top level and the actual work in a functional style: 1: Your GameState type can itself be made into a monad. Take a look at the All About Monads tutorial, especially the State monad. Think about the invariants in GameState; can you produce a new monad that guarantees these invariants through a limited set of actions. How do these actions correspond to user perceptions? 2: You can layer monads by using monad transformers. Extend the solution to part 1 by using StateT IO instead of just State. 3: Your current design uses a random number generator in the IO monad. Someone already suggested moving that into the GameState. But you can also generate an infinite list of random numbers. Can you make your game a function of a list of random numbers? 4: User input can also be considered as a list. Haskell has lazy input, meaning that you can treat user input as a list that actually only gets read as it is required. Can you make your game a function of the list of user inputs? How does this interact with the need to present output to the user? What about the random numbers? Good luck, Paul. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] bytea decoding
2008/1/20 Bryan Green [EMAIL PROTECTED]: Does anyone know of a library that will handle bytea encodings from postgres? The bytea field that I need to access contains a jpg file. I want to retrieve it from the database and write it out for an image display program. I'd love to see Don give the correct ByteString solution, but here's a slow version I knocked up (probably buggy): import qualified Data.ByteString as B import Data.ByteString.Internal (c2w) import Data.Maybe (catMaybes) import Data.List (mapAccumL) byteaDecode :: B.ByteString - B.ByteString byteaDecode = B.pack . catMaybes . snd . mapAccumL f initState . B.unpack where initState = (0, 0) f (0, _) 92 = ((1, 0), Nothing) f (0, _) x = ((0, 0), Just x) f (1, _) 92 = ((0, 0), Just 92) f (3, n) x = ((0, 0), Just (n * 8 + (x - 48))) f (c, n) x = ((c + 1, n * 8 + (x - 48)), Nothing) AGL -- Adam Langley [EMAIL PROTECTED] http://www.imperialviolet.org 650-283-9641 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Data.Binary questions
Hi, I'm relatively new to Haskell so please bear with me. I'm trying to parse Java class files with Data.Binary and I'm having a few problems: (The class file format is described here: http://java.sun.com/docs/books/jvms/second_edition/html/ClassFile.doc.html and the bytecode instructions are described here: http://java.sun.com/docs/books/jvms/second_edition/html/Instructions.doc.html ) 1. The class file format contains a number of tables. The table definitions start with the length of the list and carry on with that many table entries. Lists would be a good representation for them in Haskell, because there is not need to index them directly (except with the constants table). I've created my own list type so that I can redefine the serialisation functions for it so that the serialisation matches the format defined in the class file format: newtype MyList e = MkList ([e]) deriving Show instance (Binary e) = Binary (MyList e) where put (MkList es) = do put (fromIntegral (length es) :: Word16) mapM_ put es get = do n - get :: Get Word16 xs - replicateM (fromIntegral n) get return (MkList xs) The problem is that one of the tables, namely the attribute_info structures, use a u32 length field whereas all the other tables use a u16 length field. My implementation uses u16, but it would be nice to be able to use the same data type for both types of tables. I think I can do it by adding a lenght field to MyList and specifying the type when I use MyList in some other data structure, but that would also mean that I have to keep track of the length of the list manually? I'm basically copy-pasting the same code just to use a u32 length field in the serialised form: data Info = MkInfo [Word8] deriving Show instance Binary Info where put (MkInfo xs) = do put (fromIntegral (length xs) :: Word32) mapM_ put xs get = do n - get :: Get Word32 xs - replicateM (fromIntegral n) get return (MkInfo xs) 2. This is the bigger problem. The Java class file contains a constants table in the beginning of the file. The other fields later on in the class file contain indexes that reference entries in that constants table. So in order to be able to replace an index in a data structure with the actual string, I need to be able to look up the string from the constants table while I'm deserialising the field. My guess is that I should be able to put the constants table into a state monad. On the other hand Data.Binary already uses the state monad for holding onto the binary data being deserialised. So it's not clear to me if I can use StateT with Data.Binary.Get? And if not, can I implement my own state monad and do it that way? I'm not very comfortable with Monads yet, so I might be missing something very obvious. This is what the get function looks like in my top-level Data.Binary instance: get = do magic - get :: Get Word32 case magic == magicNumber of -- class files start with 0xCAFEBABE True - do min - get -- minor version number u16 maj - get -- major version number u16 c - get -- constants table a - get -- access flags (public, abstract, ...) u16 t - get -- a u16 index pointing to the name of this class in the constants table s - get -- a u16 index pointing to the name of the super class in the constants table i - get -- a table of interfaces f - get -- a table of fields m - get -- a table of methods attrs - get -- a table of class level attributes return (ClassFile (min, maj) c a t s i f m attrs) False - error Invalid magic number Thanks for all the help! -- ! Lauri ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary questions
On Sun, 2008-01-20 at 18:18 +, Lauri Pesonen wrote: Hi, I'm relatively new to Haskell so please bear with me. I'm trying to parse Java class files with Data.Binary and I'm having a few problems: (The class file format is described here: http://java.sun.com/docs/books/jvms/second_edition/html/ClassFile.doc.html and the bytecode instructions are described here: http://java.sun.com/docs/books/jvms/second_edition/html/Instructions.doc.html ) 1. The class file format contains a number of tables. The table definitions start with the length of the list and carry on with that many table entries. Lists would be a good representation for them in Haskell, because there is not need to index them directly (except with the constants table). I've created my own list type so that I can redefine the serialisation functions for it so that the serialisation matches the format defined in the class file format: newtype MyList e = MkList ([e]) deriving Show instance (Binary e) = Binary (MyList e) where put (MkList es) = do put (fromIntegral (length es) :: Word16) mapM_ put es get = do n - get :: Get Word16 xs - replicateM (fromIntegral n) get return (MkList xs) The problem is that one of the tables, namely the attribute_info structures, use a u32 length field whereas all the other tables use a u16 length field. My implementation uses u16, but it would be nice to be able to use the same data type for both types of tables. I think I can do it by adding a lenght field to MyList and specifying the type when I use MyList in some other data structure, but that would also mean that I have to keep track of the length of the list manually? You may want to consider using the other side of Data.Binary rather than the Binary class. The -class- Binary is intended for de/serialization when you don't care about the format. From the documentation: For parsing and generating simple external binary formats (e.g. C structures), Binary may be used, but in general is not suitable for complex protocols. Instead use the Put and Get primitives directly. Nevertheless, one way to solve your problem is with a phantom type. Change MyList to, newtype MyList t e = MkList [e] deriving Show getLengthType :: MyList t e - t getLengthType = undefined instance (Binary e) = Binary (MyList t e) where put l@(MkList es) = do put (fromIntegral (length es) `asTypeOf` getLengthType l) mapM_ put es get = do n - get xs - replicateM (fromIntegral (n `asTypeOf` getLengthType t)) get return (MkList xs `asTypeOf` t) where t = undefined The asTypeOfs are just to propagate the type information around. GHC's extension for scoped type variables would make this code simpler and more direct. At any rate, now the code will use the Binary instance for whatever type t is to serialize the length. 2. This is the bigger problem. The Java class file contains a constants table in the beginning of the file. The other fields later on in the class file contain indexes that reference entries in that constants table. So in order to be able to replace an index in a data structure with the actual string, I need to be able to look up the string from the constants table while I'm deserialising the field. My guess is that I should be able to put the constants table into a state monad. On the other hand Data.Binary already uses the state monad for holding onto the binary data being deserialised. So it's not clear to me if I can use StateT with Data.Binary.Get? And if not, can I implement my own state monad and do it that way? I'm not very comfortable with Monads yet, so I might be missing something very obvious. If you mean that you there references to the constant table in e.g. the fields table then the problem here is that you need to the class methods to use that monad transformer (in this case, ReaderT is all you should need and not even that), but you can't change their type. These are the kind of issues that make the Binary class unsuitable for this type of work. If that is the case, the only way to use this is to explicitly write out the deserialization code rather than relying on get, i.e. you'll have to write a function 'getTable constantTable' that will deserialize the table. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] CPP and INLINE pragmas
Since CPP mode removes newlines in the out macro expansion. It appears
to be impossible to have a macro expand to a function with an INLINE
pragma since it appears to need to be in its own line.
For example:
#define GETHOSTWORD(name, m, type) \
{-# INLINE name #-} \
name :: m type ; \
name = getPtr (sizeOf (undefined :: type)) \
Does work (since you can't follow the INLINE pragma with anything else
on the same line.
Likewise:
#define GETHOSTWORD(name, m, type) \
name :: m type ; \
name = getPtr (sizeOf (undefined :: type)) \
{-# INLINE name #-}
Also doesn't work since the INLINE needs to start at the beginning of a line.
Has anyone a workaround for this, or a way to get the preprocessor to
output a newline?
Cheers
AGL
--
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http://www.imperialviolet.org 650-283-9641
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Re: [Haskell-cafe] Hangman game
Hi Paul, You gave some suggestions of other styles of Haskell programming that Ronald could try for his program. These styles are definitely worth knowing, so if Ronald is not familiar with them, he may want to try them out. However, in most cases, I think what Ronald already did is nicer than what you are suggesting. Paul Johnson wrote: The design reads very much like a straight translation from the imperative style, which is why so much of it is in the IO monad. There is nothing wrong with this for a simple game like Hangman, but for larger games it doesn't scale. It's a state monad, and most of his code is in that style. It doesn't read to me like imperative style at all. And it scales beautifully. There is a lot of liftIO, because that is the bulk of the work in this program. But Ronald cleanly separated out the game logic, and even the pure parts of the UI logic, into pure functions like handleGuess and renderGameState. I personally might have kept a more consistently monadic style by writing those as pure monads, like: handleGuess :: MonadState GameState m = Char - m () renderGameState :: MonadState GameState m - m String In certain situations, that approach gives more flexiblity. Like for refactoring, or adding new features. But Ronald's approach is also very nice, and I might also do that. 1: Your GameState type can itself be made into a monad. Yes, it can. But StateT GameState IO is the perfect monad for this game - writing a new monad would just be reinventing the wheel. It would certainly be a good learning experience for understanding the inner workings of the state monad transformer, though. 2: You can layer monads by using monad transformers. Extend the solution to part 1 by using StateT IO instead of just State. I think he is already using that type. 3: Your current design uses a random number generator in the IO monad. Someone already suggested moving that into the GameState. But you can also generate an infinite list of random numbers. Can you make your game a function of a list of random numbers? He could, but I would advise against that technique. In more complex games, you may need to do many different kinds of random calculations in complex orders. Keeping a random generator inside a state monad is perfect for that. And since Ronald already set up the plumbing for the state monad, he is already home. Generating an infinite list from a random generator burns up the generator, making it unusable for any further calculations. Sometimes that doesn't matter, but I think it's a bad habit. I admit you'll catch me doing it sometimes though, in quick and dirty situations like at the GHCi prompt. 4: User input can also be considered as a list. Haskell has lazy input, meaning that you can treat user input as a list that actually only gets read as it is required. Can you make your game a function of the list of user inputs? How does this interact with the need to present output to the user? What about the random numbers? That type of lazy IO is considered by many to be one of Haskell's few warts. It is a hole in the type system that lets a small amount of side-effects leak through, and even that small amount leads to bugs. In many situations it's hard to avoid without making a wreck out of your whole program structure (though more and more tools are becoming available to help, such as the ByteString stuff). Ronald did great without it - why resort to that? All that said - this is clearly a matter of taste, of course. Thanks for bringing up a variety of approaches. Regards, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANN: A triple of new packages for talking tothe outside world
On Jan 15, 2008 7:33 PM, Adam Langley [EMAIL PROTECTED] wrote: Ok, no TH ;) I've just uploaded binary-strict 0.2.2 to Hackage which factors most of the common code out via CPP. Hopefully I didn't break anything. AGL -- Adam Langley [EMAIL PROTECTED] http://www.imperialviolet.org 650-283-9641 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Throwback of inferred types
On Sunday 20 January 2008 21:02:04 [EMAIL PROTECTED] wrote: On 2008.01.19 19:11:13 +0100, Peter Verswyvelen [EMAIL PROTECTED] scribbled 1.4K characters: I would find it most useful to get type inference information on the fly, even when not all of the code compiles correctly yet. Does that make sense? If the code doesn't compile, then how could any type-inference be trustable? Note that this functionality continues to be widely used in other functional languages, e.g. SML, OCaml, F#. I can't think why Haskell would be any different. -- Dr Jon D Harrop, Flying Frog Consultancy Ltd. http://www.ffconsultancy.com/products/?e ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Parsec benchmarks
I'd like to compare the performance of Parsec to other parsers but the only reference to a benchmark I have found is a dead link from one of the papers about Parsec: http://research.microsoft.com/users/daan/download/parsec/parsec.pdf Are there any surviving Parsec benchmarks? -- Dr Jon D Harrop, Flying Frog Consultancy Ltd. http://www.ffconsultancy.com/products/?e ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Throwback of inferred types
On 2008.01.19 19:11:13 +0100, Peter Verswyvelen [EMAIL PROTECTED] scribbled 1.4K characters: The problem is that this only works when the complete source file compiles correctly no? Yes. As I said, it's a very hackish solution - think of it as proof-of-concept. I would find it most useful to get type inference information on the fly, even when not all of the code compiles correctly yet. Does that make sense? If the code doesn't compile, then how could any type-inference be trustable? It might be reliable if the error is in definitions which don't get called or otherwise used by the function you are asking after, but there are going to be edge-cases, I should think, where it would bite you. -- gwern Freeh ASU 32 CIO GGL Force 97 b in Macintosh pgpjicjhzpFeX.pgp Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parsec benchmarks
On Jan 20, 2008 9:54 PM, Jon Harrop [EMAIL PROTECTED] wrote: I'd like to compare the performance of Parsec to other parsers but the only reference to a benchmark I have found is a dead link from one of the papers about Parsec: http://research.microsoft.com/users/daan/download/parsec/parsec.pdf Are there any surviving Parsec benchmarks? I'm very interested in a common benchmark which I could try my ByteString implementation of Parsec against. -- Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Throwback of inferred types
[EMAIL PROTECTED] wrote: Does that make sense? If the code doesn't compile, then how could any type-inference be trustable? Why, of course it is trustable, because it's going to fail, and that means that the code has type a - _|_. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Throwback of inferred types
On Sunday 20 January 2008 22:06:04 Duncan Coutts wrote: On Sun, 2008-01-20 at 21:02 +, Jon Harrop wrote: On Sunday 20 January 2008 21:02:04 [EMAIL PROTECTED] wrote: On 2008.01.19 19:11:13 +0100, Peter Verswyvelen [EMAIL PROTECTED] scribbled 1.4K characters: I would find it most useful to get type inference information on the fly, even when not all of the code compiles correctly yet. Does that make sense? If the code doesn't compile, then how could any type-inference be trustable? Note that this functionality continues to be widely used in other functional languages, e.g. SML, OCaml, F#. I can't think why Haskell would be any different. Really? That's pretty cool. How does it work? With OCaml you compile with the -dtypes option and inferred types are available in the IDE. For example, in Emacs you hit C+C C+T to get the type of the subexpression under the cursor. In OCaIDE, this is provided as graphical throwback of the subexpression under the mouse in Eclipse and repeat type checking passes are automated. In F#, the Visual Studio mode provides the same functionality. I believe MLton provides the same functionality for SML. Does it use Achim's suggestion of replacing expressions which fail to type with new type vars and at runtime an error message with the type error? I believe it just dumps the types of all subexpressions to file with source code locations as they are inferred. In the case of broken code, the given type is either non-existant (nothing is given because nothing has been inferred), more general that it should be (because later unifications have not yet been made) or wrong (which is most valuable when debugging type errors). Or do they use something more hacky that we could also implement quickly? OCaml generates .annot files that look like this: nth.ml 6 68 78 nth.ml 6 68 91 type( string - int Gram.Entry.t ) nth.ml 6 68 92 nth.ml 6 68 97 type( int Gram.Entry.t ) nth.ml 6 68 92 nth.ml 6 68 97 type( string ) nth.ml 6 68 72 nth.ml 6 68 97 type( int Gram.Entry.t ) That would be cool. Then I can run the bits of my program that still work. It'd make the editor/interpreter session rather more live. Exactly. How close do the IDEs/emacs-modes for SML, OCaml, F# come to that? What are we missing out on? :-) You're missing out on a lot if this isn't available for Haskell yet. I didn't realise just how invaluable this is until a system upgrade broke it and I really struggled to write OCaml code without it: I don't know how I managed before! Some people argue that functional programming languages don't need decent development environments but, having used F#, I know better... -- Dr Jon D Harrop, Flying Frog Consultancy Ltd. http://www.ffconsultancy.com/products/?e ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Throwback of inferred types
On Sun, 2008-01-20 at 21:02 +, Jon Harrop wrote: On Sunday 20 January 2008 21:02:04 [EMAIL PROTECTED] wrote: On 2008.01.19 19:11:13 +0100, Peter Verswyvelen [EMAIL PROTECTED] scribbled 1.4K characters: I would find it most useful to get type inference information on the fly, even when not all of the code compiles correctly yet. Does that make sense? If the code doesn't compile, then how could any type-inference be trustable? Note that this functionality continues to be widely used in other functional languages, e.g. SML, OCaml, F#. I can't think why Haskell would be any different. Really? That's pretty cool. How does it work? Does it use Achim's suggestion of replacing expressions which fail to type with new type vars and at runtime an error message with the type error? Or do they use something more hacky that we could also implement quickly? like: foo = 3 bar = 'c' baz = foo + bar So we infer: foo :: Int foo = 3 bar :: Char bar = 'c' baz :: a baz = error No instance for (Num Char) arising from a use of `+' at foo.hs:5:6-14 That would be cool. Then I can run the bits of my program that still work. It'd make the editor/interpreter session rather more live. How close do the IDEs/emacs-modes for SML, OCaml, F# come to that? What are we missing out on? :-) Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] CPP and INLINE pragmas
Adam Langley wrote:
Since CPP mode removes newlines in the out macro expansion. It appears
to be impossible to have a macro expand to a function with an INLINE
pragma since it appears to need to be in its own line.
that's because INLINE uses layout like everything else, so you can use
semicolons for it too.
For example:
#define GETHOSTWORD(name, m, type) \
{-# INLINE name #-} \
name :: m type ; \
name = getPtr (sizeOf (undefined :: type)) \
something like
#define GETHOSTWORD(name, m, type) \
{-# INLINE name #-} ; \
name :: m type ; \
name = getPtr (sizeOf (undefined :: type)) \
~Isaac
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Re: [Haskell-cafe] Throwback of inferred types
On 20 Jan 2008, at 1:02 PM, [EMAIL PROTECTED] wrote: On 2008.01.19 19:11:13 +0100, Peter Verswyvelen [EMAIL PROTECTED] scribbled 1.4K characters: The problem is that this only works when the complete source file compiles correctly no? Yes. As I said, it's a very hackish solution - think of it as proof- of-concept. I would find it most useful to get type inference information on the fly, even when not all of the code compiles correctly yet. Does that make sense? If the code doesn't compile, then how could any type-inference be trustable? It might be reliable if the error is in definitions which don't get called or otherwise used by the function you are asking after, but there are going to be edge- cases, I should think, where it would bite you. Even if it's not reliable, the compiler gives its error messages based on some form of partial type inference. It would be quite interesting, some times, to see what the compiler thinks the types are, when it gives a type error (this bit me recently trying polymorphic recursion: I had a long list of polymorphic functions defined without type signatures (since the names were clear enough), factored out some duplicated code, and wound up with a set of mutually recursive functions, one of which was polymorphically recursive. I'll dig the example up if you want (it's kind of compilcated). Knowing that the compiler had various types inferred correctly would have helped me zero in on the place I needed a type signature (or at least I remember wanting to find such things out at the time)). jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] CPP and INLINE pragmas
Adam Langley [EMAIL PROTECTED] writes: Has anyone a workaround for this, or a way to get the preprocessor to output a newline? You can use cpphs with the --layout flag, to preserve newlines in macro expansion. http://haskell.org/cpphs For instance, with ghc you need to add the following flags: ghc -cpp -pgmPcpphs -optP--cpp -optP--layout Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] CPP and INLINE pragmas
Thanks Isaac and Malcolm. That neatly solves all my problems! AGL -- Adam Langley [EMAIL PROTECTED] http://www.imperialviolet.org 650-283-9641 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First go at reactive programming
This fixed the second example. Thanks. I think handleConnection should be handleConnection :: RequestHandler - Handle - IO () handleConnection r h = handleToRequest h = responseSend h . runRequestHandler r Levi ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] bug in all about monads tutorial
Since nobody with write access to that page seems to be responding here, you may wish to try reporting this bug to the main Haskell mailing list ([EMAIL PROTECTED]). Posting to that list may get the attention of some Haskell users who may not regularly read this mailing list. Benjamin L. Russell --- Peter Hercek [EMAIL PROTECTED] wrote: Hi, About 3 weeks ago I reported this bug to Jeff Newbern. But I got no response - maybe I got filtered out as spam :) Since it was not fixed I'm trying once more here. Maybe there is somebody here who has access to the web site http://www.haskell.org/all_about_monads and cares enough to fix it. On page http://www.haskell.org/all_about_monads/html/writermonad.html there is listens defined like this: listens f m = do (a,w) - m; return (a,f w) ... but it should be like this: listens f m = do (a,w) - listen m; return (a,f w) ... or maybe a less strict option (as ghc libs have it): listens f m = do ~(a,w) - listen m; return (a,f w) Peter. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Invitation for MathematiKa '08 : projectEuler format
Hello Math Enthusiast, IIIT-Hyderabad, India cordially invites you to be a part of Mathematika '08, an online competition that emphasizes on fusion of mathematics and computing. Where: http://felicity.iiit.ac.in/~math When: 4th February, 2008 This Online Math Contest will consist of 10-12 problems made randomly from different domains of existing Math. All problem statements will be visible to the contestant from the start of contest spanning over a 10 hour period. The solution to each problem would be an integer or a floating point number which is to be submitted in real-time. One Minute Rule: The problems are designed in a way that support 1 minute rule which means that an efficient implementation will allow a solution to be obtained on a modestly powered computer in less than one minute. Also, make sure to bring your appetite for math, programming and fun. There will be plenty of all three to go around. Regards Mathematika Team http://felicity.iiit.ac.in/~math ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
