July 2002 - Haskell - Haskell.org

RE: deriving instances for "hidden" types
by Simon Peyton-Jones 30 Jul '02

30 Jul '02

Look on my home page! http://research.microsoft.com/~simonpj Simon | -----Original Message----- | From: Scott J. [mailto:jscott@planetinternet.be] | Sent: 30 July 2002 01:01 | To: Simon Peyton-Jones | Cc: haskell(a)haskell.org | Subject: Re: deriving instances for "hidden" types | | | Is Template Haskell a new form of Haskell? And where can I | find documentation about it? | | SCott

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RE: deriving instances for "hidden" types
by Simon Peyton-Jones 30 Jul '02

30 Jul '02

| I've often felt a tinge of disappointment not being able to | derive classes over data structures that are defined in the | libraries (DeepSeq FiniteMap, for instance). I was wondering | if any of the tools (drift, etc.) or GHCs built-in meta | programming would allow you to say something like: | | derive (DeepSeq a, DeepSeq b) => DeepSeq (FiniteMap a b) I think Hal was only suggesting doing this in case where the representation of the data structure was visible to the library client. (As others have said, it's not a good idea if the rep is abstract.) Template Haskell will be able to do this. Heart transplant operation is in progress. Blood on floor, but patient still alive. Simon

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by �� F�rsat� 28 Jul '02

28 Jul '02

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deriving instances for "hidden" types
by Hal Daume III 26 Jul '02

26 Jul '02

I've often felt a tinge of disappointment not being able to derive classes over data structures that are defined in the libraries (DeepSeq FiniteMap, for instance). I was wondering if any of the tools (drift, etc.) or GHCs built-in meta programming would allow you to say something like: derive (DeepSeq a, DeepSeq b) => DeepSeq (FiniteMap a b) where the compiler or something "knows" the representation of FiniteMap even if we don't. I don't know if something like this would be possible, but if so, I'd find it very useful. On the same note, if NFData/DeepSeq instances could be provided for all the library types, I'd really appreciate it (FiniteMap, Array, etc...). -- Hal Daume III "Computer science is no more about computers | hdaume(a)isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume

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overloaded num types, but not string types?
by Hal Daume III 26 Jul '02

26 Jul '02

I was wondering if anyone's thought of overloading string literals in the same way that numeric literals are overloaded. I know that I tend to use PackedStrings for almost everything, primarly due to the RegExp stuff and efficiency. This means my code is littered with "unpackPS" and "packString", as in ... if foo == packString "bar" ... or ... if unpackPS foo == "bar" ... I was wondering if someone might consider overloading Strings, too. Something like: class StringLiteral s where fromString :: String -> s toString :: s -> String -- not necessary, really then literals in haskell source could be converted from ... "foo" ... to ... (fromString "foo") ... we'd have instances like instance StringLiteral String where fromString = id instance StringLiteral PackedString where fromString = packString ...etc... if not something in ghc, perhaps this might find its way into drift??? - hal -- Hal Daume III "Computer science is no more about computers | hdaume(a)isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume

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Re: SURVEY - Haskell editing
by C.Reinke 26 Jul '02

26 Jul '02

[reply-to set to refactor-fp(a)ukc.ac.uk] Just for info - the current state: we got about 30 responses in the first few days, but the rate of new entries has dropped since then. The survey will be open till the end of July (Wednesday next week), so if you want to add your input, you've still got some time. Thanks to everyone who has already responded, Claus > As some of you know, our refactoring project here at UKC has just > started (at long last). Of course, it will take some time before > this leads to concrete artifacts in terms of detailed refactoring > catalogues and prototype tools, but we would like to know a bit more > about the environment into which any such refactoring tools would > have to fit. After all, you might have different development habits > and tools than we do;-) > > So it would be great if you could spare a few minutes to fill in > the following survey and send it back to <refactor-fp(a)ukc.ac.uk> > (reply-to should be set?). We'll summarize to this list. > > We will try to keep you involved in later stages of the project as > well, e.g., to ask for input on what refactorings you'd find most > useful, but if you'd like to share your thoughts on this earlier, > feel free to email us. > > Thanks for your input, > Claus > > "Refactoring Functional Programs" > http://www.cs.ukc.ac.uk/research/groups/tcs/fp/Refactor/ > > > ----------July 2002---------------------- SURVEY - Haskell editing > > 1. When developing Haskell programs, > > - which OS-platforms do you work on? > > - which Haskell implementations are you using (please indicate rough > version info: "whatever", "latest source release", "latest binary > release", "latest CVS", "latest stable version", ..)? > > Hugs98 > GHC > nhc98 > .. > > - to what extent do you use (which?) features outside Haskell 98? > > class/instance-restrictions > existential types > arrow notation > .. > > - what editors, IDEs or source-manipulation tools are you using? > > - editors > Vim > Emacs > .. > > - tag-file generators > HaskTags > .. > > - documentation generators > Haddock > .. > > - pre-processors > DrIFT > cpp > .. > > - revision control > manual > CVS > bitkeeper > .. > > - .. > > 2. To what extent are your editors/IDEs Haskell-aware? > > - what Haskell-specific functionality do they offer? > > syntax highlighting > pretty-printing > tag-files permitting jump-to-definition > syntax-aware movements (to next definition/expression/..) > .. > > - what non-Haskell-specific editing functionality do you find most > helpful when developing Haskell programs? > > matching of parentheses > macro recording and playback (what do you use these for?) > integration with external tools (which ones?) > .. > > - what Haskell-specific editing functionality do you you miss most? > > .. > > - what interface options does your editor/IDE offer for integration > of external tools (brief explanations or pointers to detailed > documentations would be great)? > > coarse-grained (piping text through formatters, spell-checkers; > preparation of tag files, ..) > fine-grained (bi-directional access, i.e., editor can use > external functionality, and external tools can use editor > functionality) > scripting (to weave it all together) > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell

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Where do you put hClose when using hgetContents ?
by kyagrd 26 Jul '02

26 Jul '02

Since hgetContents is lazy, closing the file with hClose makes the result of hgetContents to be unexpected. Where should the hClose be put ? -- Ahn Ki-yung

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input format for heap profiler hp2ps?
by nr＠eecs.harvard.edu 25 Jul '02

25 Jul '02

We're working on a heap profiler, and we'd like to use the hp2ps program that was developed by David Wakeling and is distributed with GHC. Unfortunately, the man page is, shall we way, a bit terse on the subject of the input format expected by hp2ps. How should we discover more information about the proper input format? Norman

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Uluslararas� �� FIRSATI..
by �� F�rsat� 25 Jul '02

25 Jul '02

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Bug in library report
by Simon Peyton-Jones 25 Jul '02

25 Jul '02

Folks, Another small but long-standing bug in the Haskell Library report: the recursive calls to 'reads' and 'shows' in the Read and Show instances for Ratio and Array should be calls to readsPrec and showsPrec respectively. The corrected defintions are below. (c.f. the example of derived instances in Appendix D of the language report.) Anyone disagree? (How do these bugs last so long?) Simon ================== Page 5 ======================== instance (Read a, Integral a) => Read (Ratio a) where readsPrec p = readParen (p > prec) (\r -> [(x%y,u) | (x,s) <- readsPrec (prec+1) r, ("%",t) <- lex s, (y,u) <- readsPrec (prec+1) t ]) instance (Integral a) => Show (Ratio a) where showsPrec p (x:%y) = showParen (p > prec) (showsPrec (prec+1) x . showString " % " . showsPrec (prec+1) y) ================== Page 24 ======================== instance (Ix a, Show a, Show b) => Show (Array a b) where showsPrec p a = showParen (p > arrPrec) ( showString "array " . showsPrec (arrPrec+1) (bounds a) . showChar ' ' . showsPrec (arrPrec+1) (assocs a) ) instance (Ix a, Read a, Read b) => Read (Array a b) where readsPrec p = readParen (p > arrPrec) (\r -> [ (array b as, u) | ("array",s) <- lex r, (b,t) <- readsPrec (arrPrec+1) s, (as,u) <- readsPrec (arrPrec+1) t ]) -- Precedence of the 'array' function is that of application itself arrPrec = 10

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