- Libraries - Haskell.org

Fwd: [GHC] #1960: Add Applicative and Monoid instances for STM
by Conal Elliott 08 Dec '07

08 Dec '07

Is STM part of the libraries(a)haskell.org charter? ---------- Forwarded message ---------- From: GHC <trac(a)galois.com> Date: Dec 5, 2007 2:57 PM Subject: [GHC] #1960: Add Applicative and Monoid instances for STM To: Cc: glasgow-haskell-bugs(a)haskell.org #1960: Add Applicative and Monoid instances for STM -------------------------------+-------------------------------------------- Reporter: conal | Owner: Type: proposal | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 6.8.1 Severity: normal | Keywords: Difficulty: Easy (1 hr) | Testcase: Architecture: Unknown | Os: Unknown -------------------------------+-------------------------------------------- {{{ instance Applicative STM where { pure = return; (<*>) = ap } instance Monoid (STM a) where { mempty = retry; mappend = orElse } }}} I don't know where these instances would go. Nor whether this is a libraries or GHC proposal. -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1960> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Documentation and HAppS
by Chris Smith 08 Dec '07

08 Dec '07

I'm making an offer. I need to learn HAppS extremely well over the next couple months. I am willing to document the process by attempting to write detailed documentation on developing applications with HAppS. Something on the order that could be eventually combined into a book, or at least an extensive searchable web site. My current thoughts are to either: 1. Find a free wiki site to do it. 2. Use HaskellWiki 3. Coordinate with Alex regarding the HAppS web site I'm not sure which would be most appropriate. My hope would be to make this public early, since I'm bound to make some mistakes or leave some things out. So I'm sort of counting on getting comments from people who know more than me. Finally, I'm not sure whether code currently in a sufficiently good state that it would be reasonable to write something like this. Perhaps I should hold off and wait for things to stabilize. So: - Is this something people would find helpful? - Should I do it now, or wait? - Which of the choices (1), (2), or (3) above do you think best of? Thanks, -- Chris Smith

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mtl documentation - external link broken
by apfelmus 07 Dec '07

07 Dec '07

Hello, In the documentation for the monad transformer library, the hyperlink http://www.cse.ogi.edu/~mpj/ to Mark P. Jones' homepage is broken. It's used to reference his paper Functional Programming with Overloading and Higher-Order Polymorphism The new location is http://web.cecs.pdx.edu/~mpj/ Regards, apfelmus

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Cabal, System.Filepath
by Peter Gammie 07 Dec '07

07 Dec '07

To my surprise, if you type ^C at the right moment you can trash GHC's (system-wide) package list. I figured it was easier to reinstall than fix, but forgot Debian installs GHC 6.6 if I don't ask for "unstable". So, let's get Cabal on its feet again: $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.6 $ darcs pull Pulling from "http://darcs.haskell.org/cabal"... No remote changes to pull in! $ ghc -i. --make Setup.lhs -o setup Distribution/Simple.hs:114:7: Could not find module `System.FilePath': Use -v to see a list of the files searched for. Can I humbly suggest that Cabal rely on very few external libraries? (I'm switching to 6.6.1 as I type this.) cheers peter

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who are the contributors to the Unix package?
by Galchin Vasili 07 Dec '07

07 Dec '07

Hello, Who started this effort? Who is currently doing work on the Unix package? Kind regards, Vasya

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Re: Bounded and floating types
by Conal Elliott 06 Dec '07

06 Dec '07

Oops -- I'd incorrectly assumed that Haskell guarantees Float & Double to have infinities. Thanks, - Conal On Dec 2, 2007 9:50 AM, Lennart Augustsson <lennart(a)augustsson.net> wrote: > But that only makes sense for floating point types that have -Infinity and > +Infinity. > > On Dec 2, 2007 5:39 PM, Conal Elliott <conal(a)conal.net> wrote: > > > Currently Float & Double do not have standard Bounded instances. Is > > there any reason not to use the following? > > > > instance Bounded Float where { minBound = -1/0; maxBound = 1/0 } > > instance Bounded Double where { minBound = -1/0; maxBound = 1/0 } > > > > If I don't hear objections, I'll submit a ticket and re-send a proposal > > note. > > > > - Conal > > > > > > _______________________________________________ > > Libraries mailing list > > Libraries(a)haskell.org > > http://www.haskell.org/mailman/listinfo/libraries > > > > >

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System.Random: enumRandomR, boundedEnumRandom
by Henning Thielemann 05 Dec '07

05 Dec '07

Did you also already need Random instances of enumerations? Wouldn't it be nice to have some helper functions in System.Random: enumRandomR :: (Enum a, RandomGen g) => (a,a) -> g -> (a,g) enumRandomR (l,r) = mapFst toEnum . randomR (fromEnum l, fromEnum r) boundedEnumRandom :: (Enum a, Bounded a, RandomGen g) => g -> (a,g) boundedEnumRandom = enumRandomR (minBound, maxBound) mapFst :: (a -> c) -> (a,b) -> (c,b) mapFst f ~(x,y) = (f x, y) Example application: instance Random Day where random = boundedEnumRandom randomR = enumRandomR

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Proposal: Bounded instance for IntSet (ticket #1953)
by David Benbennick 05 Dec '07

05 Dec '07

>From http://hackage.haskell.org/trac/ghc/ticket/1953 : I propose to add a Bounded instance to IntSet.hs. IntSet is in Ord, and there are only finitely many instances of IntSet. Therefore there is a min IntSet and a max IntSet. It turns out these bounds are very simple: instance Bounded IntSet where minBound = empty maxBound = singleton maxBound Suggested deadline: December 16, 2007.

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GHC's CPP and Cabal's unlit
by Alistair Bayley 05 Dec '07

05 Dec '07

I'm doing some testing with GHC 6.6.1 and Cabal 1.3, and I'm trying to figure out what happens with CPP and Cabal's unlit. I start with file Test.lhs: > {-# OPTIONS -fglasgow-exts #-} > module Test where > main = putStrLn "hello CPP" and run command: ghc -E -x hs -cpp Test.lhs -o Test2.lhs which gives me Test2.lhs: {-# LINE 1 "Test.lhs" #-} # 1 "Test.lhs" # 1 "<built-in>" # 1 "<command line>" # 1 "Test.lhs" > {-# OPTIONS -fglasgow-exts #-} > module Test where > main = putStrLn "hello CPP" So I'm wondering: where does the {-# LINE #-} comment come from, and also the # 1 lines? AFAICT the # 1 lines are ignored by GHC; I can compile Test2.lhs without errors. Is there anything in GHC's docs about this? More puzzling is that the files that Cabal runs through ghc's CPP don't get the # n lines, so we end up with something like this: {-# LINE 1 "Test.lhs" #-} > {-# OPTIONS -fglasgow-exts #-} > module Test where > main = putStrLn "hello CPP" which is not a valid .lhs file, because we have a code line next to a comment. I also note in Cabal the haddock command runs CPP before unlit. GHC does it the other way around i.e. run unlit first then CPP, and I'm wondering if Cabal shouldn't do the same thing? Thanks, Alistair

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Maybe Monoid spilt milk
by Conor McBride 04 Dec '07

04 Dec '07

Hi folks I realise I should have been paying more attention last March, and as such have no reason to expect any sympathy, let alone action. I would, however, like to comment on the fact that the Data.Monoid instance for (Maybe x) prioritises monoidal structure from x over monoidal structure from Maybe. This makes it hard to use generic monoidal operations to support choice in the Maybe monad. I don't know if this breaks anybody else's code, but it certainly breaks mine. I guess I'll just have to stop using Data.Monoid and roll my own. That's not a serious hardship, I suppose. I have only myself to blame, and I'm not proposing that the Maybe behaviour is changed. I suppose people are busy enjoying the instance as it now stands, and that it would be damaging to change. What a pity Conor http://www.cs.nott.ac.uk/~ctm This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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