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Build failure for PortMidi on mac: incorrect Block.h
by Brian Victor 13 Aug '10

13 Aug '10

I'm trying to build PortMidi on the mac, and get the error shown below. It appears that an OSX header is trying to include a Block.h file and getting the GHC Block.h instead of the one it expects. I'm new to Haskell and even newer to cabal, so I'm not sure how to go about solving this. Incidentally, cabal, cabal-install, and the system PortMidi libraries are all up-to-date. %cabal install PortMidi Resolving dependencies... Configuring PortMidi-0.1.3... Preprocessing library PortMidi-0.1.3... Building PortMidi-0.1.3... [1 of 1] Compiling Sound.PortMidi ( Sound/PortMidi.hs, dist/build/Sound/PortMidi.o ) In file included from /System/Library/Frameworks/CoreServices.framework/Frameworks/CarbonCore.framework/Headers/FSEvents.h:28, from /System/Library/Frameworks/CoreServices.framework/Frameworks/CarbonCore.framework/Headers/CarbonCore.h:218, from /System/Library/Frameworks/CoreServices.framework/Frameworks/AE.framework/Headers/AE.h:20, from /System/Library/Frameworks/CoreServices.framework/Headers/CoreServices.h:21, from portmidi/pm_mac/pmmacosxcm.c:38:0: /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/include/Block.h:51:0: error: expected specifier-qualifier-list before ‘StgPtr’ /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/include/Block.h:108:0: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘bdescr’ /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/include/Block.h:163:0: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘void’ /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/include/Block.h:174:0: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘void’ /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/include/Block.h:187:0: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘void’ /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/include/Block.h:198:0: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘void’ /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/include/Block.h:219:0: error: expected ‘)’ before ‘n’ /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/include/Block.h:223:0: error: expected ‘)’ before ‘n’ /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/include/Block.h:235:0: error: expected declaration specifiers or ‘...’ before ‘nat’ /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/include/Block.h:241:0: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘StgWord’ cabal: Error: some packages failed to install: PortMidi-0.1.3 failed during the building phase. The exception was: exit: ExitFailure 1 -- Brian

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ANN: hswip-0.3 embedding swi-prolog in haskell
by Evgeny Tarasov 13 Aug '10

13 Aug '10

I would like to announce a small library hswip. It is an analogue of pyswip [1] python library in haskell. Hswip allows to embed swi-prolog [2] interpreter into your haskell applications in a convenient way. Let't look at an example: main = do prologInit ["-q","-nosignals"] prologCall "asserta(a(b,c))." prologCall "asserta(parent(pam, bob))." prologCall "asserta(parent(tom, bob))." prologCall "asserta(parent(tom, liz))." prologCall "asserta(parent(bob, ann))." prologCall "asserta(parent(bob, pat))." prologCall "asserta(parent(pat, jim))." res <- prologCall "parent(X,Y)." print res Output: [[("X","pat"),("Y","jim")],[("X","bob"),("Y","pat")],[("X","bob"),("Y","ann")],[("X","tom"),("Y","liz")],[("X","tom"),("Y","bob")],[("X","pam"),("Y","bob")]] The library still has alpha quality and there are many things missing including exception handling and BSD license. Any feedback is welcome! -Evgeny Tarasov [1] http://code.google.com/p/pyswip/ [2] http://www.swi-prolog.org/ [3] http://hackage.haskell.org/package/hswip-0.3

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Twidge Short URL not working...
by arn-arn fernch 13 Aug '10

13 Aug '10

Hello, It's my first time using this mailing list thing so forgive me if I made any mistakes. I was using Twidge (http://wiki.github.com/jgoerzen/twidge/) and it's mentioned there is an available support in the Haskell Cafe. I only have a slight problem with Twidge. It's currently not shortening URLs by default though I can see in my .twidgerc this line "shortenurls: yes". Any things I should consider? Thanks!

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universal quantification is to type instantiations as existential quantification is to what
by Joshua Ball 13 Aug '10

13 Aug '10

Hi, If I have a universally quantified type mapInt :: forall a. (Int -> a) -> [Int] -> [a] I can instantiate that function over a type and get a beta-reduced version of the type mapInt [String] :: (Int -> String) -> [Int] -> [String] (I'm borrowing syntax from Pierce here since I don't think Haskell allows me to explicitly pass in a type to a function.) This makes sense to me. The universal quantifier is basically a lambda, but it works at the type level instead of the value level. My question is... what is the analog to an existential type? mapInt :: exists a. (Int -> a) -> [Int] -> [a] (I don't think this is valid syntax either. I understand that I can rewrite this using foralls and a new type variable, doing something that looks like double negation, but the point of my question is to get an intuition for what exactly the universal quantifier means in the context of function application... if this even makes sense.) In particular: 1. If I can "instantiate" variables in a universal quantifier, what is the corresponding word for variables in an existential quantifier? 2. If type instantiation of a universally quantified variable is beta-reduction, what happens when existentially quantified variables are [insert answer to question 1]? 3. Is there any analogue to existential quantifiers in the value world? "Forall" is to "lambda" as "exists" is to what? Also (separate question), is the following statement true? forall T :: * -> *. (forall a. T a) -> (exists a. T a) If so, what does the implementation look like? (What function inhabits it, if it is interpreted as a type?) Josh "Ua" Ball

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Re: Documentation for OpenGL?
by Eitan Goldshtrom 13 Aug '10

13 Aug '10

Woops, nevermind. I WAS looking in the wrong place. I should've known =P. Sorry for the unnecessary request. -Eitan PS. For anyone interested all of the documentation is in Graphics.Rendering.OpenGL.GL.PerFragment on hackage

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Documentation for OpenGL?
by Eitan Goldshtrom 13 Aug '10

13 Aug '10

Hi everyone. I'm looking for something specific. I'm trying to figure out how to use the depthFunc StateVar and I can't find any official documentation for it. I did a ":t depthFunc" in ghci and got "depthFunc :: StateVar (Maybe ComparisonFunction)" so I looked up ComparisonFunction and couldn't find anything official on that either. Is there any documentation for it? Maybe I wasn't looking in the right places? Thanks in advance. -Eitan

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How do you change the mouse position?
by Eitan Goldshtrom 13 Aug '10

13 Aug '10

In C++, maybe Java, I remember using a Robot to change the location of the mouse on the screen. My intention is to do something like in an FPS game where the mouse is always centered to make sure it doesn't run into the edges of the screen. How can I do that in Haskell? I'm using OpenGL, so if there is a utility that specifically works with OpenGL then I believe that would be the most helpful. -Eitan

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ghc in macports
by Ozgur Akgun 12 Aug '10

12 Aug '10

Dear Cafe, I wonder who is maintaining the ghc package in macports, and what the current stategy of doing things is? http://www.macports.org/ports.php?by=name&substr=ghc (ghc 6.10.4) Personally, I'd like to use the macports version, if the ghc version there was resonably recent (having 2 versions, a stable and an edge could be a good idea?) Thanks, Ozgur

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ADT patch/update
by Sergey Mironov 12 Aug '10

12 Aug '10

Hi Cafe. I am searching for materials on one data type-related problem. Suppose we have version control system storing values of user-defined algebraic data type. 'User' (actually, programmer) wants to store his/her data and later update it by applying patches. By patch I mean value of some (another) type representing one simplest update of stored value. Say, for tree type > data Tree a = Node (Tree a) (Tree a) | Leaf a one may write > {-# LANGUAGE TypeFamilies #-} > {-# LANGUAGE UndecidableInstances #-} > > class Storable a where > type Patch a :: * > update :: Patch a -> a -> a > > data TreeStep = Left | Right -- Like in zippers ? > type family Location a :: * > type instance Location (Tree a) = [TreeStep] > > instance (Storable a) => Storable (Tree a) where > type Patch (Tree a) = (Location (Tree a), Patch a) > update = ... -- Move to specific location and call node's update Patch here is coded explicitly but I guess there may be some generic way of it to calculate. Whether any similar work has been carried out? Will be glad to read comments! -- Thanks, Sergey

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hackage.haskell.org cannot be accessed?
by Magicloud Magiclouds 12 Aug '10

12 Aug '10

Hi, Today I found out that I cannot access hackage.haskell.org. I have tried vpn/proxy to see if my network has something wrong. No luck. -- 竹密岂妨流水过山高哪阻野云飞

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