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Warnings with OverloadedLists
by Nikolay Amiantov 18 Jun '14

18 Jun '14

Hello, I've bumped into strange GHC behaviour with OverloadedLists and pattern matching. Consider this example: {-# LANGUAGE OverloadedLists #-} len :: [a] -> Int len [] = 0 len (_:t) = 1 + len t If I load this with "ghci -Wall", I get a warning: Test.hs:4:1: Warning: Pattern match(es) are non-exhaustive In an equation for ‘len’: Patterns not matched: [] If I disable OverloadedLists extension, warning goes away. Can someone clear this behaviour out for me? It looks like a bug, but I'm not sure. Thanks for help, Nikolay.

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Support of multi-constructor types by UNPACK pragma
by Nikita Volkov 18 Jun '14

18 Jun '14

Currently the pragma only supports single-constructor types. So in the following example it will simply be ignored: data A = A1 Char | A2 {-# UNPACK #-} !B data B = B1 Int | B2 Bool However it seems to be easily solvable by changing the type A to something like the following during unpacking: data A = A1 Char | A2_1 Int | -- from B1 A2_2 Bool -- from B2 Am I missing something? Why is it not implemented?

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ANN: haddock-library 1.0.0
by Mateusz Kowalczyk 18 Jun '14

18 Jun '14

Hi, haddock-library is a package aiming to provide bits of Haddock to the rest of the Haskell world without imposing the GHC dependency that we have on the ‘haddock’ package itself. Please note that this does not deprecate the ‘haddock’ package which aims to expose other bits of Haddock, including those talking with GHC. Specifically, 1.0.0 exposes the types used by the comment parser and the parser itself. This allows you to supply the Haddock parser with String and get a Haddock ADT back out to play with. This means that if in the past you were processing Haddock strings with your own solution (or copy + pasted Alex parser we had) then you should now switch to this package instead. The API is subject to change so upper version bound is advised. Tested on 7.6.3, 7.8.x and current HEAD. The parser exposed is what is used in Haddock itself which now internally depends on this package. There are plans to move more parts into this package, exposing as much useful functionality as possible without the GHC dependency. New releases are independent of the GHC release cycle, unlike Haddock itself. To file issues for this package, use the Haddock issue tracker that's now on GitHub. Thanks -- Mateusz K.

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return with mutable object
by Baojun Wang 18 Jun '14

18 Jun '14

Hi List, Per my understanding, return x would make a new copy of the object. What if the returned object is mutable? Will this make a new (mutable) object? My concern is if I created a very large mutable object, does return mutable make a full copy of the original mutable data, or just copy a reference (pointer?)? Thanks baojun

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"Spinless Tagless G-Machine" erratum?
by Tom Ellis 17 Jun '14

17 Jun '14

I am reading SPJ's seminal work "Implementing lazy functional languages on stock hardware: the Spinless Tagless G-machine" (1992) and I am confused by something which may be a minor notational error, or may be a key detail I am misunderstanding. The paper is available here http://citeseer.ist.psu.edu/viewdoc/summary?doi=10.1.1.53.3729 On page 26 we have aList = {} \n Cons {thing,nil} nil = {} \n Nil {} but I have not seen this use of the notation elsewhere in the paper. It strikes me that this should be aList = {} \n {} -> Cons {thing,nil} nil = {} \n {} -> Nil {} Is my intuition correct, or am I missing a key detail? Thanks, Tom

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Package Maintenance: hfuse
by Montez Fitzpatrick 17 Jun '14

17 Jun '14

I would like to take over maintenance of the following package: "hfuse." I have attempted to e-mail the original package author and maintainer with no response.

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Fwd: testing platform
by Roelof Wobben 17 Jun '14

17 Jun '14

Hello, IM learning Haskell by this book : Programming Haskell. Which test platform can I also learn the best or can I better first learn Haskell and later the test platforms ? Roelof

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1 = 0?
by Alexey Muranov 17 Jun '14

17 Jun '14

Is this the expected behavior that 1 = 0 does not raise any error? What does this mean? Thanks. Alexey.

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data/newtype vs. class
by martin 16 Jun '14

16 Jun '14

Hello all, I find myself trying to define a class, where a newtype would suffice. E.g. once I was pondering over "named" things and my initial thought was "well that's a class, which asks for a function 'getName'". But then here http://www.haskell.org/pipermail/haskell-cafe/2010-June/078803.html someone showed me a solution without any classes. Recently I was pondering over "timed things" (things which change at specific ponts in time) and again my initial thought was "that's a class, which asks for a method 'at'". Then I remembered things like State, i.e. data types which wrap around functions. State is not a class, which asks for a function 'nextState', it is all defined with data. Can someone give me some guidance, when to use classes and when to use data? Are the two concepts interchangeable in some scenarios? Martin

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Re: [Haskell-cafe] Uploading to hackage fails: bad file names in tarball
by Niklas Larsson 16 Jun '14

16 Jun '14

Hi! For extremely ancient and cludgy reasons AUX isn't a valid filename on windows, it's a DOS device. The other similarly reserved name are CON, PRN and NUL. Niklas ----- Ursprungligt meddelande ----- Från: "Arie Peterson" <ariep(a)xs4all.nl> Skickat: ‎2014-‎06-‎16 10:45 Till: "haskell-cafe(a)haskell.org" <haskell-cafe(a)haskell.org> Ämne: [Haskell-cafe] Uploading to hackage fails: bad file names in tarball Since some time, I have been unable to upload packages to Hackage, via either the 'cabal upload' command, or using the web form. The error message it gives is this: ==== ✂ ==== Hackage username: AriePeterson Hackage password: Uploading dist/np-linear-0.1.1.1.tar.gz... Error: dist/np-linear-0.1.1.1.tar.gz: 400 Bad Request Error: Invalid package Invalid windows file name in tar archive: "np-linear-0.1.1.1\\src\\Aux.hs". For portability, hackage requires that file names be valid on both Unix and Windows systems, and not refer outside of the tarball. ==== ✂ ==== The tarball is created by 'cabal sdist': cabal-install version 1.18.0.2 using version 1.18.1.1 of the Cabal library. I also installed the newest cabal-install, on another machine, but this did not help (same error). I also tried to create a tarball by hand, using 'tar --format=ustar', but this again resulted in the same error message. By the way, I'm on linux, not Windows, so it is not clear how the backslashes get in the file names. What could be going on? _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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