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Problem installing curl
by Martin Huschenbett 11 Nov '08

11 Nov '08

Hi all, when I try to install curl (needed for hxt) using "cabal install curl" I alwas get the following error message: Resolving dependencies... 'curl-1.3.2.1' is cached. Configuring curl-1.3.2.1... cabal: Error: some packages failed to install: curl-1.3.2.1 failed during the configure step. The exception was: sh: runGenProcess: does not exist (No such file or directory) I don't know what to do here. Can anybody help me please? I'm using the brand new GHC 6.10.1 on Windows Vista. Best regards, Martin.

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compilation question
by Peter Padawitz 11 Nov '08

11 Nov '08

At first a type of arithmetic expressions and its generic evaluator: data Expr = Con Int | Var String | Sum [Expr] | Prod [Expr] | Expr :- Expr | Int :* Expr | Expr :^ Int data ExprAlg a = ExprAlg {con :: Int -> a, var :: String -> a, sum_ :: [a] -> a, prod :: [a] -> a, sub :: a -> a -> a, scal :: Int -> a -> a, expo :: a -> Int -> a} eval :: ExprAlg a -> Expr -> a eval alg (Con i) = con alg i eval alg (Var x) = var alg x eval alg (Sum es) = sum_ alg (map (eval alg) es) eval alg (Prod es) = prod alg (map (eval alg) es) eval alg (e :- e') = sub alg (eval alg e) (eval alg e') eval alg (n :* e) = scal alg n (eval alg e) eval alg (e :^ n) = expo alg (eval alg e) n Secondly, a procedural version of eval (in fact based on continuations): data Id a = Id {out :: a} deriving Show instance Monad Id where (>>=) m = ($ out m); return = Id peval :: ExprAlg a -> Expr -> Id a peval alg (Con i) = return (con alg i) peval alg (Var x) = return (var alg x) peval alg (Sum es) = do as <- mapM (peval alg) es; return (sum_ alg as) peval alg (Prod es) = do as <- mapM (peval alg) es; return (prod alg as) peval alg (e :- e') = do a <- peval alg e; b <- peval alg e'; return (sub alg a b) peval alg (n :* e) = do a <- peval alg e; return (scal alg n a) peval alg (e :^ n) = do a <- peval alg e; return (expo alg a n) My question: Is peval less time- or space-consuming than eval? Or would ghc, hugs et al. optimize eval towards peval by themselves? Peter

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Re: [Haskell-cafe] Calling Haskell from other languages?
by Donn Cave 11 Nov '08

11 Nov '08

Quoth Colin Paul Adams <colin(a)colina.demon.co.uk>: | Is there a way to call Haskell code from other languages? I have looked on | the wiki, and as far as I can see, it only talks about the other way | round (when Haskell is the main program). There sure is a way to call from other languages - cf. "foreign export" - but don't know how hard it would be to make Haskell live without its "main", which performs a lot of runtime initialization. For me (with nhc98) it's a lot easier to use a Haskell "main" that's just a brief wrapper: module Main (main) where import NHC.FFI foreign import ccall "cmain" cmain :: IO () main = cmain (... where "cmain" is an external entry point in the C code, which can then call Haskell as required.) Donn

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announce: Workflow-0.1
by Alberto G. Corona 11 Nov '08

11 Nov '08

I needed to to define multiuser web workflows in the most transparent way. I wondered if a state monad could transparently bring automatic checkpointing of each action and automatic resume after failure. In this way a long living computation could be expressed in a single monadic computation. Additionally, for inter process communications, this package includes a primitive for activating a workflow whenever any action result meet certain condition. There are also primitives for start/restart processes, retrieval of intermediate results and unsafe IO actions inside the state monad... http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Workflow Cabal description: Transparent low level support (state logging, resume of the computation, wait for data condition) for long living, event driven processes. Workflow give the two first services to any monadic computation of type (a-> m a) usually m=IO f x >>=\x'-> g x' >>= \x''->... z by prefixing the user with the method "step": step f x >>= \x'-> step g x' >>= \x''->... This means that a workflow can be described with the familiar "do" notation. In principle, there is no other limitation on the syntax but the restriction (a -> m a): All computations consume and produce the same type of data. do notation is supported fully. Workflow export a few primitives that bring the following services: - transparent checkpointing of each step in permanent storage using TCache (step) - resume of the monadic computation at the last checkpoint after soft or hard interruption - use of versioning techniques for storing object changes (using RefSerialize) - retrieval of the object at any previous step - suspend the computation (waitFor) until the input object meet certain conditions. useful for inter-workflow comunications. At the end of the workflow all the intermediate data is erased. see demos and the header of Control.TCache for documentation. This is a piece of code is a loop that imput numbers (demo.hs). there is another process, that check the numbers entered and return Finish when match the desired number. that is detected by this thread and finalize. When number of tries are 9, The process finish, this is detected by the other process and finalizes also. That ilustrates the use of event handling (waitFor) and step execution. askNumbers name d = do step2 $ threadDelay 5000 -- wait for the other tread to process. r <- step (waitFor anything) d -- get the last value of the object with key "try-finish", to look for the other thread actions case r of Finish msg -> step2 $ print msg --the other thread sent a finalize response Try 9 num -> step1 $ return $ Finish "sorry, no more guesses" --send finalization to the wait thread _ -> do nd <- step (askNumber name) d askNumbers name nd where anything= \_-> True

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GHC 6.10 / Mac OS X / Library problem
by Pieter Laeremans 11 Nov '08

11 Nov '08

Hello, I've got a problem when I want to install pcre-light on OS X, with the latest version of GHC (binary package from haskell.org) It is not clear to me which flags to pass to ghc, to tell it to look at /opt/local/include for the pcre-light.h header. Any suggestions ? thanks, Pieter :cabal-install-0.6.0 pieter$ sudo cabal install pcre-light Password: Resolving dependencies... 'pcre-light-0.3.1' is cached. Configuring pcre-light-0.3.1... Preprocessing library pcre-light-0.3.1... Base.hsc:103:18: error: pcre.h: No such file or directory Base.hsc: In function 'main': Base.hsc:401: error: 'PCRE_ANCHORED' undeclared (first use in this function) Base.hsc:401: error: (Each undeclared identifier is reported only once Base.hsc:401: error: for each function it appears in.) Base.hsc:404: error: 'PCRE_AUTO_CALLOUT' undeclared (first use in this function) Base.hsc:407: error: 'PCRE_CASELESS' undeclared (first use in this function) Base.hsc:410: error: 'PCRE_DOLLAR_ENDONLY' undeclared (first use in this function) Base.hsc:413: error: 'PCRE_DOTALL' undeclared (first use in this function) Base.hsc:416: error: 'PCRE_DUPNAMES' undeclared (first use in this function) Base.hsc:419: error: 'PCRE_EXTENDED' undeclared (first use in this function) Base.hsc:422: error: 'PCRE_EXTRA' undeclared (first use in this function) Base.hsc:425: error: 'PCRE_FIRSTLINE' undeclared (first use in this function) Base.hsc:428: error: 'PCRE_MULTILINE' undeclared (first use in this function) Base.hsc:431: error: 'PCRE_NEWLINE_CR' undeclared (first use in this function) Base.hsc:434: error: 'PCRE_NEWLINE_CRLF' undeclared (first use in this function) Base.hsc:437: error: 'PCRE_NEWLINE_LF' undeclared (first use in this function) Base.hsc:440: error: 'PCRE_NO_AUTO_CAPTURE' undeclared (first use in this function) Base.hsc:443: error: 'PCRE_UNGREEDY' undeclared (first use in this function) Base.hsc:446: error: 'PCRE_UTF8' undeclared (first use in this function) Base.hsc:449: error: 'PCRE_NO_UTF8_CHECK' undeclared (first use in this function) Base.hsc:621: error: 'PCRE_NOTBOL' undeclared (first use in this function) Base.hsc:624: error: 'PCRE_NOTEOL' undeclared (first use in this function) Base.hsc:627: error: 'PCRE_NOTEMPTY' undeclared (first use in this function) Base.hsc:633: error: 'PCRE_PARTIAL' undeclared (first use in this function) Base.hsc:631: error: 'PCRE_ERROR_NOMATCH' undeclared (first use in this function) Base.hsc:634: error: 'PCRE_ERROR_NULL' undeclared (first use in this function) Base.hsc:637: error: 'PCRE_ERROR_BADOPTION' undeclared (first use in this function) Base.hsc:640: error: 'PCRE_ERROR_BADMAGIC' undeclared (first use in this function) Base.hsc:643: error: 'PCRE_ERROR_UNKNOWN_NODE' undeclared (first use in this function) Base.hsc:646: error: 'PCRE_ERROR_NOMEMORY' undeclared (first use in this function) Base.hsc:649: error: 'PCRE_ERROR_NOSUBSTRING' undeclared (first use in this function) Base.hsc:652: error: 'PCRE_ERROR_MATCHLIMIT' undeclared (first use in this function) Base.hsc:655: error: 'PCRE_ERROR_CALLOUT' undeclared (first use in this function) Base.hsc:658: error: 'PCRE_ERROR_BADUTF8' undeclared (first use in this function) Base.hsc:661: error: 'PCRE_ERROR_BADUTF8_OFFSET' undeclared (first use in this function) Base.hsc:664: error: 'PCRE_ERROR_PARTIAL' undeclared (first use in this function) Base.hsc:667: error: 'PCRE_ERROR_BADPARTIAL' undeclared (first use in this function) Base.hsc:670: error: 'PCRE_ERROR_INTERNAL' undeclared (first use in this function) Base.hsc:673: error: 'PCRE_ERROR_BADCOUNT' undeclared (first use in this function) Base.hsc:676: error: 'PCRE_ERROR_DFA_UITEM' undeclared (first use in this function) Base.hsc:679: error: 'PCRE_ERROR_DFA_UCOND' undeclared (first use in this function) Base.hsc:682: error: 'PCRE_ERROR_DFA_UMLIMIT' undeclared (first use in this function) Base.hsc:685: error: 'PCRE_ERROR_DFA_WSSIZE' undeclared (first use in this function) Base.hsc:688: error: 'PCRE_ERROR_DFA_RECURSE' undeclared (first use in this function) Base.hsc:691: error: 'PCRE_ERROR_RECURSIONLIMIT' undeclared (first use in this function) Base.hsc:665: error: 'PCRE_INFO_OPTIONS' undeclared (first use in this function) Base.hsc:668: error: 'PCRE_INFO_SIZE' undeclared (first use in this function) Base.hsc:671: error: 'PCRE_INFO_CAPTURECOUNT' undeclared (first use in this function) Base.hsc:674: error: 'PCRE_INFO_BACKREFMAX' undeclared (first use in this function) Base.hsc:677: error: 'PCRE_INFO_FIRSTBYTE' undeclared (first use in this function) Base.hsc:680: error: 'PCRE_INFO_FIRSTCHAR' undeclared (first use in this function) Base.hsc:683: error: 'PCRE_INFO_FIRSTTABLE' undeclared (first use in this function) Base.hsc:686: error: 'PCRE_INFO_LASTLITERAL' undeclared (first use in this function) Base.hsc:689: error: 'PCRE_INFO_NAMEENTRYSIZE' undeclared (first use in this function) Base.hsc:692: error: 'PCRE_INFO_NAMECOUNT' undeclared (first use in this function) Base.hsc:695: error: 'PCRE_INFO_NAMETABLE' undeclared (first use in this function) Base.hsc:698: error: 'PCRE_INFO_STUDYSIZE' undeclared (first use in this function) Base.hsc:701: error: 'PCRE_INFO_DEFAULT_TABLES' undeclared (first use in this function) Base.hsc:690: error: 'PCRE_CONFIG_UTF8' undeclared (first use in this function) Base.hsc:693: error: 'PCRE_CONFIG_NEWLINE' undeclared (first use in this function) Base.hsc:696: error: 'PCRE_CONFIG_LINK_SIZE' undeclared (first use in this function) Base.hsc:699: error: 'PCRE_CONFIG_POSIX_MALLOC_THRESHOLD' undeclared (first use in this function) Base.hsc:702: error: 'PCRE_CONFIG_MATCH_LIMIT' undeclared (first use in this function) Base.hsc:705: error: 'PCRE_CONFIG_STACKRECURSE' undeclared (first use in this function) Base.hsc:708: error: 'PCRE_CONFIG_UNICODE_PROPERTIES' undeclared (first use in this function) Base.hsc:711: error: 'PCRE_CONFIG_MATCH_LIMIT_RECURSION' undeclared (first use in this function) Base.hsc:724: error: 'PCRE_EXTRA_STUDY_DATA' undeclared (first use in this function) Base.hsc:727: error: 'PCRE_EXTRA_MATCH_LIMIT' undeclared (first use in this function) Base.hsc:730: error: 'PCRE_EXTRA_CALLOUT_DATA' undeclared (first use in this function) Base.hsc:733: error: 'PCRE_EXTRA_TABLES' undeclared (first use in this function) Base.hsc:736: error: 'PCRE_EXTRA_MATCH_LIMIT_RECURSION' undeclared (first use in this function) compiling dist/build/Text/Regex/PCRE/Light/Base_hsc_make.c failed command was: /usr/bin/gcc -c -D__GLASGOW_HASKELL__=610 -I/Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.1/bytestring-0.9.1.4/include -I/Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.1/base-4.0.0.0/include -I/Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.1/include -IPAPI_INCLUDE_DIR dist/build/Text/Regex/PCRE/Light/Base_hsc_make.c -o dist/build/Text/Regex/PCRE/Light/Base_hsc_make.o cabal: Error: some packages failed to install: pcre-light-0.3.1 failed during the building phase. The exception was: exit: ExitFailure 1 -- Pieter Laeremans <pieter(a)laeremans.org> "The future is here. It's just not evenly distributed yet." W. Gibson

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Exporting a Type Class for Type Signatures
by Dominic Steinitz 11 Nov '08

11 Nov '08

In the crypto package, I have two functions > encrypt :: AESKey a => a -> Word128 -> Word128 > decrypt :: AESKey a => a -> Word128 -> Word128 which are exported. I also have > class (Bits a, Integral a) => AESKey a > > instance AESKey Word128 > instance AESKey Word192 > instance AESKey Word256 unexported which stops you using invalid keys. Someone has asked me to export AESKey as they want to write an explicit type signature for a function they are creating e.g. foo :: AESKey a => a -> Word128 -> Word128 foo x y = encrypt x y but this generates an error. Is there a way of allowing someone to use AESKey in a type signature but not allow them to declare new instances? Thanks, Dominic.

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download haskell?
by Johannes Waldmann 11 Nov '08

11 Nov '08

This is nit-picking, but ... when I go to haskell.org, there is a link (top in the left menu) "Download Haskell". Is this for readers who don't know the meaning of the word "implementation" (a few lines below)? Ah, it must be modelled after the perl.org start page... - J.W.

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Histogram creation
by Alexey Khudyakov 11 Nov '08

11 Nov '08

Hello! I'm tryig to write efficient code for creating histograms. I have following requirements for it: 1. O(1) element insertion 2. No reallocations. Thus in place updates are needed. accumArray won't go because I need to fill a lot of histograms (hundrends) from vely long list of data (possibly millions of elements) and it will traverse input data for each histogram. It seems that I need to use mutable array and/or ST monad or something else. Sadly both of them are tricky and difficult to understand. So good examples or any other ideas greatly appreciated. -- Alexey Khudyakov

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Closed type classes [was: Exporting a Type Class for Type Signatures]
by oleg＠okmij.org 11 Nov '08

11 Nov '08

Dominic Steinitz wrote: > In the crypto package, I have two functions > > encrypt :: AESKey a => a -> Word128 -> Word128 > > decrypt :: AESKey a => a -> Word128 -> Word128 but the class AESKey is not exported, to prevent the user from adding more instances to it. Since AESKey is not exported, the users cannot write signatures that mention that class constraint. The question is, how to export a _closed_ class -- a class the user cannot extend. Chung-chieh Shan and I had a similar problem in our TFP2007 paper: the classes that implement type-level arithmetic must be closed, to prevent the user from declaring that 1+1=1. It seems the best method is to use class aliases: In the implementation of AES, introduce class AESKey a => AESKeyExport a instance AESKey a => AESKeyExport a -- the only instance and now export AESKeyExport (but leave AESKey hidden). If the user needs to write the signature for their function: foo :: AESKeyExport a => a -> Word128 -> Word128 foo x y = encrypt x y they should use the constraint AESKeyExport a. That constraint entails AESKey a, which they cannot mention. The users can try to extend the class ESKeyExport a, but that would do them no good: the library uses the instances of AESKey rather than AESKeyExport. The TFP2007 paper explains that in a bit more detail: http://okmij.org/ftp/Computation/resource-aware-prog/tfp.pdf (Section 2.1). It also mentions a different method, relying on partial type signatures.

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A video of Frag
by Korcan Hussein 11 Nov '08

11 Nov '08

I don't understand why there is no video of Frag online so I made one here: http://uk.youtube.com/watch?v=0jYdu2u8gAU _________________________________________________________________ BigSnapSearch.com - 24 prizes a day, every day - Search Now! http://clk.atdmt.com/UKM/go/117442309/direct/01/

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