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Error Message when trying to solve alphametic(SEND + MORE = MONEY)
by Sok Ha Chang 27 Jan '14

27 Jan '14

Hi. I’m new to Haskell. Use Haskell Platform on MacBook Air. $ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.6.3 I’m try to solve alphametic. SEND + MORE = MONEY Here is code… ---------------------------------------------------------------------------------------------------------- import Data.List decryp :: [Int] -> String -> String decryp (s:e:n:d:o:r:y:[]) a = if send + more == money then expr:a else a where send = s * 1000 + e * 100 + n * 10 + d more = 1000 + o * 100 + r * 10 + e money = 10000 + o * 1000 + n * 100 + e * 10 + y expr = show send ++ "+" ++ show more ++ "=" show money decrypSolver :: [String] decrypSolver = foldr decryp [] (permutations 7 [0, 2, 3, 4, 5, 6, 7, 8, 9]) ---------------------------------------------------------------------------------------------------------- Error Messages is ./decrypSolver.hs: line 10, column 60: Couldn't match expected type `(a0 -> String) -> Int -> [Char]' with actual type `[Char]' The function `"="' is applied to two arguments, but its type `[Char]' has none In the second argument of `(++)', namely `"=" show money' In the second argument of `(++)', namely `show more ++ "=" show money’ ---------------------------------------------------------------------------------------------------------- How can I fix this? Thank you. Sincerely, S. Chang

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Re: [Haskell-beginners] Just started working with Haskell. Need some help
by Pyro Crane 22 Jan '14

22 Jan '14

Hello again. Thank you all for your very helpful replies (below) Here is the error I got when I tried to run my script : Could not find module `Graphics.GD' Locations searched: Graphics/GD.hs Graphics/GD.lhs As with the previous errors, I went on Google, to find out which module and/or package I needed to install. Apparently, I need something called "GD" When I tried : cabal install gd I got the following : Resolving dependencies... Configuring gd-3000.7.3... cabal-1.16.0.2: Missing dependencies on foreign libraries: * Missing (or bad) header file: gd.h * Missing C libraries: gd, expat Failed to install gd-3000.7.3 cabal-1.16.0.2: Error: some packages failed to install: gd-3000.7.3 failed during the configure step. The exception was: ExitFailure 1 Upon further inquiries via google, I found somewhere the following : This problem can usually be solved by installing the system packages that provide these libraries (you may need the "-dev" versions). If the libraries are already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are. I thought I did this already. But, apparently, I did something wrong?? -----Original Message----- From: beginners-request <beginners-request(a)haskell.org> To: beginners <beginners(a)haskell.org> Sent: Sat, Jan 18, 2014 11:35 pm Subject: Beginners Digest, Vol 67, Issue 19 Message: 1 Date: Sat, 18 Jan 2014 12:25:01 -0500 (EST) From: Pyro Crane <pyrocrane1(a)aol.com> To: beginners(a)haskell.org Subject: [Haskell-beginners] Just started working with Haskell. Need some help Message-ID: <8D0E2895A21535B-1058-8B60(a)webmail-d276.sysops.aol.com> Content-Type: text/plain; charset="us-ascii" Hi, I just started working with Haskell Running it on a RHEL linux operating system I was able to download and install it, along with libraries and packages (or, at least, what I thought were the libraries and packages) But, when I try to run a simple script, I keep getting the error : "Could not find module XXXXXX".............. I understand what this error means ---- there is a package/library missing. I tried using the "Cabal Update" command, but this did not solve the problem. So, I am now fixing this problem the primitive way, as follows : (a) I use Google to first find out what the missing module is (b) then, based on what google says, I am able to determine the name of the actual package that needs to be installed (c) I use "Cabal Install" to install the package (d) I try to run the script again (e) I get the same error, but this time, it cannot find a different module (f) I go back to Google to locate the missing module etc, etc, etc, etc Obviously, this is as slow as it is ridiculous............... especially when one considers that there are probably hundreds of these modules/packages And, now, I've come up against a module/package, which I am unable to locate in Google. It's missing from my installation, and Google does not know what it is, or where I can find it Is there any way to simply install ALL required packages??? I thought I already did this, but obviously I missed something Thanks

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Follow @HaskellTips
by Kim-Ee Yeoh 21 Jan '14

21 Jan '14

@HaskellTips is a twitter account just launched by Jon Fischoff, a member of the community. It looks to have useful tidbits of Haskell programming folklore that anyone who's done enough hacking in it acquires. Eventually. But following the twitter account should give you a leg-up in the process. If you prefer an email feed, here's one way: 1) Use StreamSpigot to get a web page like this: http://www.streamspigot.com/tweet-digest/digest?usernames=HaskellTips&outpu… 2) Use your favorite website-change-detection service to get deltas via email. For e.g. search "web page changes". If you're stumped by anything @HaskellTips, feel free to discuss it here! -- Kim-Ee

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Introduction to FFI by wrapping MurmurHash3
by Courtney Robinson 19 Jan '14

19 Jan '14

Just thought I'd share a lib I've put together and the blog post I wrote about it http://haskell.zcourts.com/ffi/2014/01/19/haskell-foerign-function-interfac… The package is available on Hackage http://hackage.haskell.org/package/Dish And API docs for MurmurHash3 at http://hackage.haskell.org/package/Dish-0.0.0.4/docs/Data-Dish-Murmur3.html It is a wrapper around MurmurHash3 at the moment but I've got some more hash related utilities I'll be adding. I'm still pretty new to Haskell so would appreciate any feedback or pointers on any gotchas I may have overlooked.

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Eg.
by willie ekaputra 19 Jan '14

19 Jan '14

Eg. how to make the translation formula ? u take a coordinate and multiply it with p Element R, so that it is translated , like 1, 3 to 2, 6 , I use a 2 as multiplicator , which is from real numbers.How to express this real number ?That is why " any number will just do ! " Regards , Wili.

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"any real numbers will just do"
by willie ekaputra 19 Jan '14

19 Jan '14

how to express that Expression in Hasski ? Tq. regards, Willie. "Sanctus Dominus ."

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Just started working with Haskell. Need some help
by Pyro Crane 18 Jan '14

18 Jan '14

Hi, I just started working with Haskell Running it on a RHEL linux operating system I was able to download and install it, along with libraries and packages (or, at least, what I thought were the libraries and packages) But, when I try to run a simple script, I keep getting the error : "Could not find module XXXXXX".............. I understand what this error means ---- there is a package/library missing. I tried using the "Cabal Update" command, but this did not solve the problem. So, I am now fixing this problem the primitive way, as follows : (a) I use Google to first find out what the missing module is (b) then, based on what google says, I am able to determine the name of the actual package that needs to be installed (c) I use "Cabal Install" to install the package (d) I try to run the script again (e) I get the same error, but this time, it cannot find a different module (f) I go back to Google to locate the missing module etc, etc, etc, etc Obviously, this is as slow as it is ridiculous............... especially when one considers that there are probably hundreds of these modules/packages And, now, I've come up against a module/package, which I am unable to locate in Google. It's missing from my installation, and Google does not know what it is, or where I can find it Is there any way to simply install ALL required packages??? I thought I already did this, but obviously I missed something Thanks

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Designing complex Haskell programs
by Courtney Robinson 14 Jan '14

14 Jan '14

I'm trying to take the training wheels of and moving more of my code base to Haskell from C++ but finding it increasingly tricky. I have a subset of a gossip protocol written in C++. When a server comes online it connects to 1 or more nodes already in the cluster and get data from them about other nodes they know of. The new node merges the information and keeps a copy of the merged view. Every so often it contacts the nodes it knows about and refreshes the merged view. It also must have the up to date view ready to be sent in response to a new node joining. I currently can't wrap my head around how to maintain this state. How would a more experienced Haskeller approach this problem? Code is OK if it demonstrates a particular point but I'm more interested in the line of thought that would go into designing a solution as I suspect that'll be more useful as I get further into the migration. As a gauge to you for my current level in Haskell. I read and understand most Haskell programs fine. I write some but currently heavily rely on hackage/hoogle docs for APIs, even some common ones. Thanks

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Initialize a data type in (Writer (Endo a)) monoid
by Dmitriy Matrosov 13 Jan '14

13 Jan '14

Hi. I have the following data type > import Data.Monoid > import Control.Monad.Writer > data Graph = Graph {graphTitle :: String, graphPoints :: [Int]} > deriving (Show) > emptyGraph :: Graph > emptyGraph = Graph {graphTitle = "", graphPoints = []} Then i want to initialize it in Writer monad using (Dual (Endo Graph)) as monoid: > type GraphM t = WriterT (Dual (Endo Graph)) t > > myGraph :: Monad t => GraphM t [Int] > myGraph = do > tell (setTitle "ab") > tell (setTitle "ABCD") > tell (modifyPoints (1 :)) > tell (modifyPoints (2 :)) > return [1, 2] and then i can use it e.g. like > getGraph :: Monad t => (GraphM t a) -> t Graph > getGraph m = do > g <- execWriterT m > return (appEndo (getDual g) emptyGraph) > > printGraph :: IO () > printGraph = getGraph myGraph >>= print And to make this work i need two functions implemented for each record of Graph: get :: Graph -> a set :: a -> Graph -> Graph I can define per-record instances of them, like > setTitle :: String -> Dual (Endo Graph) > setTitle x = Dual . Endo $ \g -> g{graphTitle = x} > > modifyPoints :: ([Int] -> [Int]) -> Dual (Endo Graph) > modifyPoints f = Dual . Endo $ \g -> let xs = graphPoints g > in g{graphPoints = f xs} but if Graph has many records, for most of them these 'set' functions ('get' functions i'll have from records) will look very similar. Is there a way how i can define all of them "in one row", i.e. using some generic 'set' implementation to which i should only pass e.g. record name or smth else? I.e. so, that above myGraph will look like .. tell(set r x) .. where r is record name (or smth else referencing particulat record) and x is value.

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Getting a variables type as a string at runtime
by Gareth Morgan 12 Jan '14

12 Jan '14

Bit of a simple question but I'm struggling to find information on this via Google. I have a sum type, when the input is type A I want to process it, when it is type B I want to return MyError "Expected type A but actually got type B". However I also have C,D,E,F, etc which should also return similar errors so don't want to hardcode this string. Is there a function I can call on a variable to get the name of the data constructor that created it? I could create a typeName function but I want to avoid boiler plate if I can. For reference what I'm actually doing is parsing Java class files. The constant pool I've represented as a map of a sum ConstantPoolEntry type (the Java constant pool for some reason skips an index on some types so can't be a simple list). Certain Java class file entries have a reference to the constant pool that must be of a specific constant type so I want to report badly formed entries to the user. Thanks, Gareth

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