April 2012 - Haskell-Cafe

Cabal try to install a package I already have
by Daniel Díaz Casanueva 29 Apr '12

29 Apr '12

Hi Cafe, today I opened the command prompt and typed "cabal install ftphs". Then I read: > Resolving dependencies... > Configuring network-2.3.0.5... And I started to feel confused. Because I already have installed that package with that version! I continued reading: > cabal: The package has a './configure' script. This requires a Unix > compatibility toolchain such as MinGW+MSYS or Cygwin. Yes, I knew this would happen! (thought I don't like it with a so common-used library) But I can't understand why cabal is trying to install network-2.3.0.5. If I type "ghc-pkg list" I can see precisely network-2.3.0.5 is installed. In fact, 2.3.0.5 is the version that comes with the Haskell Platform I recently installed (2011.4.0.0) as you can see here: http://code.haskell.org/haskell-platform/haskell-platform.cabal. Could someone, please, explain me this? I will be very glad. I was working with ghc-7.4 but I needed the network package so I switched to the Haskell Platform, because install network in Windows is painful. Yes, I read the Mitchell guide (found in http://neilmitchell.blogspot.com.es/2010/12/installing-haskell-network-libr…) but once I installed the library I was having compile time error with "unknown symbol" errors. I felt very odd so I switched this machine to the Haskell Platform. I hope someone could help me. Thanks in advance, Daniel Díaz.

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Embed Haskell
by Rosario Borda 29 Apr '12

29 Apr '12

Hi All, Is there a simple method for embed haskell in other languages, like latex? An example in quasiquotation notation: \documentclass{article} \title{Hello World} \begin{document} \maketitle Hello world! and reversed: [haskell: putStrLn reverse "Hello, World!"] \end{document} Many thanks, :) Rosario

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Automatic discovery of tests
by Graham Berks 28 Apr '12

28 Apr '12

Hi, trying to learn haskell and the associated build env. I come from a java/scala world so trying to understand the how to invoke tests. Have a cabal file that invokes a main function to execute a test. But wondering if there is any automatic discovery of tests as per junit. I have seen test-framework-th but to me that implies putting a testGroupGenerator into each module. Am i correct about that and if so is there an example of calling multiple modules tests ? Or is there a better way just to invoke specific functions prefixed with case_ prop_ etc in the entire src/test directory of the cabal build ? Thanks

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Update of haskell cafe on google groups
by Graham Berks 28 Apr '12

28 Apr '12

Has this stopped working ? Seems a bit out of date ? Thanks

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Re: [Haskell-cafe] [Haskell] ANNOUNCE: planar-graph-1.0
by Ivan Lazar Miljenovic 27 Apr '12

27 Apr '12

On 28 April 2012 11:34, Christian Höner zu Siederdissen <choener(a)tbi.univie.ac.at> wrote: > Hi, > > one minor correction: >> This probably won't be of many use to people > for bioinformatics I'd disagree ;-) I'll take a look at your library. > > (for example, RNA /secondary/ structure forms a planar graph) I stand corrected! -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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ANNOUNCE: planar-graph-1.0
by Ivan Lazar Miljenovic 27 Apr '12

27 Apr '12

I uploaded this [1] yesterday, posted the blog article [2] about it... but forgot to send a message to the lists! [1]: http://hackage.haskell.org/package/planar-graph [2]: http://ivanmiljenovic.wordpress.com/2012/04/27/announcing-planar-graph/ planar-graph is an implementation of, strangely enough, planar graphs (that is, a graph that contains an embedding on a surface, can be drawn with no edge crossings and has a specific ordering of edges). It handles graphs on planes and spheres, but I'm not sure about other surfaces (and there seems to be little demand for such). This probably won't be of many use to people, but as I described in the blog post, I've been using this as a test bed for graph library design (specifically usage of abstract node/edge identifiers, using half-edges and the serialisation/encoding setup). -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Re: [Haskell-cafe] [Haskell] ANN: Portackage - a hackage portal
by Andrew Seniuk 27 Apr '12

27 Apr '12

Hi Derek, Thanks for your comments. Yes, I am probably going to focus on making it work as a web service and stay away from platform-specific mobile apps. Not been thinking mobile much at all, since the quantities of data are taxing even to my laptop, and also I'm inclined to believe people are mostly at a laptop or desktop when coding Haskell. However, I'm planning to try server-side sorting and filtering, and compare performance. No DB is used on the server yet, but it would be simple enough I suppose -- all this is quite new territory for me. Also my shared hosting resource limits may become a problem if this gets a lot of use. On the other hand, was planning to use persistence (cookies i guess?) to save the data on the client, so that patches based on Hackage RSS could be applied incrementally. Also, I think the sorting could be faster by sending per-column lists of indices. But maybe it is just the browser rendering which is taking all the time? I'll take this opportunity to announce a few improvements: - shift-click a row to see the Hackage page (bare click does nothing) - per-column filtering widgets Presently working on getting the "last updated" column, this information is not in a .cabal file but I'm hoping it is in the TAR metadata... The link again: http://www.fremissant.net/portackage A.

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Uploading a new hsc2hs
by Thomas DuBuisson 27 Apr '12

27 Apr '12

Warning: I, not the maintainer of hsc2hs, will be uploading a trivial fix for hsc2hs to hackage (new build deps). Even after public attempts to contact anyone in charge of hsc2hs (last January) there still has been no word. Speak now or forever hold your peace. Cheers, Thomas P.S. I still think c2hs is the right philosophy even if it's too verbose.

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Annotations in abstract syntax tree
by j.romildo＠gmail.com 27 Apr '12

27 Apr '12

Hello. I need to annotate abstract syntax tree with additional information in a compiler. Using the Annotations package[1] I have written the following small program: import Annotations.F.Annotated import Annotations.F.Fixpoints data ExprF r = Num Double | Var String | Add r r | Sub r r | Mul r r | Div r r deriving (Eq,Show) type BareExpr = Fix ExprF e :: BareExpr e = In (Mul (In (Num 5)) (In (Add (In (Var "x")) (In (Num 8))))) type ValExpr = Fix (Ann Double ExprF) type Memory = [(String,Double)] eval :: Memory -> BareExpr -> ValExpr eval _ (In (Num x)) = In (Ann x (Num x)) eval m (In (Var x)) = let y = case lookup x m of Just k -> k Nothing -> 0 in In (Ann y (Var x)) eval m (In (Add x y)) = op m (+) Add x y eval m (In (Sub x y)) = op m (-) Sub x y eval m (In (Mul x y)) = op m (*) Mul x y eval m (In (Div x y)) = op m (/) Div x y op m f k x y = let x'@(In (Ann v1 _)) = eval m x y'@(In (Ann v2 _)) = eval m y in In (Ann (f v1 v2) (k x' y')) With these definitions we can represent simple arithmetic expressions and we can also evaluate them, annotating each node in the abstract syntax tree with its corresponding value. Now I want to add statements to this toy language. One statement may be a print statement containing an expression whose value is to be printed, an assign statement containing an identifier and an expression, or a compound statement containing two statements to be executed in sequence. How the data types for statements can be defined? How a function to execute an statement anotating its node with the corresponding state (memory plus output) after its execution can be defined? Without annotations the type of statements could be: data Stm = PrintStm Expr | AssignStm String Expr | CompoundStm Stm Stm How to enable annotations in this case? Note that Stm uses both Expr and Stm. [1] http://hackage.haskell.org/package/Annotations Romildo

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Automatic discovery of tests
by G 27 Apr '12

27 Apr '12

Hi, trying to learn haskell and the associated build env. I come from a java/scala world so trying to understand the how to invoke tests. Have a cabal file that invokes a main function to execute a test. But wondering if there is any automatic discovery of tests as per junit. I have seen test-framework-th but to me that implies putting a testGroupGenerator into each module. Am i correct about that and if so is there an example of calling multiple modules tests ? Or is there a better way just to invoke specific functions prefixed with case_ prop_ etc in the entire src/test directory of the cabal build ? Thanks

1 0