April 2011 - Beginners

how to make something Typeable, for Data.Dynamic?
by Rob Nikander 04 Apr '11

04 Apr '11

Hi, Can someone show me a code snippet that would make a simple record type Typeable so I can wrap one in a Data.Dynamic? I'm looking at the haddock docs and I don't see how to do it. I know to define "typeOf :: MyRecord -> TypeRep". But how to make a TypeRep? thanks, Rob

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Warnings from ghc
by Manfred Lotz 03 Apr '11

03 Apr '11

Hi there, From my experiences in programming it is usually a good thing when a compiler issues warnings because this shows me where in my code there might be future problems hidden. I found the following warnings especially important to be turned on: -fwarn-incomplete-patterns -fwarn-overlapping-patterns -fwarn-name-shadowing -fwarn-unused-matches -fwarn-unused-do-bind I see that I could turn on all warnings with -Wall but that is a bit too much. My question: what other options do people recommend to be turned on. -- Manfred

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haskell on the jvm?
by Mike Meyer 02 Apr '11

02 Apr '11

Google didn't turn up anything, so... Is there any way to compile haskell to JVM bytecodes? Dalvik, even? A gcc front end, maybe? Thanks, <mike -- Mike Meyer <mwm(a)mired.org> http://www.mired.org/consulting.html Independent Software developer/SCM consultant, email for more information. O< ascii ribbon campaign - stop html mail - www.asciiribbon.org

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Haskell Platform and GHC 7.0.3
by Alba Marchisio 02 Apr '11

02 Apr '11

Sorry I'm new and probably this post is out of topic, but my question is: when a Haskell Platform integrated with GHC 7.0.3? Thanks Alba.

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Question about functors (or maybe not...)
by Patrick LeBoutillier 02 Apr '11

02 Apr '11

Hi, I'm writing a music library and have the following types and functions: data Note = C | D | E | F | G | A | B | Sharp Note | Flat Note raise C = Sharp C data Quality = Major | Minor data Chord = Chord Quality Note -- Note is the root data Scale = Scale Quality Note -- Note is the tonic What I would like to do is to be able to lift the raise function and apply it to Chords and Scales. Something like this: fmap raise (Chord Major C) = Chord Major (Sharp C) But these are not functors as it doesn't seem to make sense for them to be polymorphic. A chord can't really made of anything except Notes. Does anybody have any ideas? Patrick -- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

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how to modify show for a list of certain types
by Manfred Lotz 02 Apr '11

02 Apr '11

Hi there, I have a list of say type Record which I write to a file and read back from the file if required. The list's content is a single line in the file it doesn't matter how many records the list contains. I would like to modify show for type Record in a way that show does work like the normal show but additionally adds a newline at the end of the string. I'm a bit lost how to do that. Any idea? -- Manfred

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Re: [Haskell-beginners] Network.HTTP basics
by Barbara Shirtcliff 01 Apr '11

01 Apr '11

Yay! Thank you! > ----- Original Message ----- > From: Daniel Fischer > Sent: 04/01/11 02:04 PM > To: beginners(a)haskell.org > Subject: Re: [Haskell-beginners] Network.HTTP basics > > On Friday 01 April 2011 21:42:19, Barbara Shirtcliff wrote: > > Hi, this is small, but this is the beginners list, so here goes: > > > > I can see how to use HTTP to request a page. for example, this works: > > > > > > Prelude Network.HTTP> let respgoogle = simpleHTTP $ getRequest > > "http://google.com" Prelude Network.HTTP> respgoogle > > Right HTTP/1.1 301 Moved Permanently > > Location: http://www.google.com/ > > Content-Type: text/html; charset=UTF-8 > > Date: Fri, 01 Apr 2011 17:31:25 GMT > > Expires: Sun, 01 May 2011 17:31:25 GMT > > Cache-Control: public, max-age=2592000 > > Server: gws > > Content-Length: 219 > > X-XSS-Protection: 1; mode=block > > Connection: close > > > > that looks really nice, but hey, what if I want to see what's in the > > content? It isn't immediately clear to me from the documentation at > > http://hackage.haskell.org/packages/archive/HTTP/4000.1.1/doc/html/Netw > > ork-HTTP.html . > > stuff = do > answer <- respgoogle > case answer of > Left connErr -> putStrLn "Got a connection error:" >> print connErr > Right result -> do > let goodies = rspBody result > putStrLn goodies -- or do something sensible > > > > > In the end, I'll be working with JSON, here, but I need to know how to > > get to it, and the examples in the documentation don't work (i.e. don't > > appear to be up to date). I'm not very experienced with Haskell, so, > > it's pretty opaque. > > > > Thanks, > > Bar > >

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Network.HTTP basics
by Barbara Shirtcliff 01 Apr '11

01 Apr '11

Hi, this is small, but this is the beginners list, so here goes: I can see how to use HTTP to request a page. for example, this works: Prelude Network.HTTP> let respgoogle = simpleHTTP $ getRequest "http://google.com" Prelude Network.HTTP> respgoogle Right HTTP/1.1 301 Moved Permanently Location: http://www.google.com/ Content-Type: text/html; charset=UTF-8 Date: Fri, 01 Apr 2011 17:31:25 GMT Expires: Sun, 01 May 2011 17:31:25 GMT Cache-Control: public, max-age=2592000 Server: gws Content-Length: 219 X-XSS-Protection: 1; mode=block Connection: close that looks really nice, but hey, what if I want to see what's in the content? It isn't immediately clear to me from the documentation at http://hackage.haskell.org/packages/archive/HTTP/4000.1.1/doc/html/Network-… . In the end, I'll be working with JSON, here, but I need to know how to get to it, and the examples in the documentation don't work (i.e. don't appear to be up to date). I'm not very experienced with Haskell, so, it's pretty opaque. Thanks, Bar

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Critique my Code!
by blackcat＠pro-ns.net 01 Apr '11

01 Apr '11

Hi, I was hoping to get a code critique from some experienced Haskell people. I put my code up in this blog post: http://learnmeahaskell.blogspot.com/2011/03/playing-around-with-quickcheck.… . thanks Lee

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Another request for code critique...
by Mike Meyer 01 Apr '11

01 Apr '11

Shorter, but thing I've done that wasn't just an exercise from a haskell book. The problem statement can be found at http://kernelbob.wordpress.com/2011/03/20/same-five-digits/. My solution can be seen at http://pastebin.com/iW95q2ex. Thanks, <mike -- Mike Meyer <mwm(a)mired.org> http://www.mired.org/consulting.html Independent Software developer/SCM consultant, email for more information. O< ascii ribbon campaign - stop html mail - www.asciiribbon.org

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