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∀ lexing in ghc and ghci
by Sean McLaughlin 18 Sep '09

18 Sep '09

Hi, I'm getting different behavior in ghci and ghc with the identifier ∀. In ghc I need to wrap it with parens, as in > (∀) :: Var -> Base -> Formula -> Formula > (∀) = All In ghci, I get an error this way Formula.lhs:112:2: Invalid type signature In ghci I can do > ∀ :: Var -> Base -> Formula -> Formula > ∀ = All fine. But then ghc complains. What's going on here? Thanks! Sean

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Thank you guys
by Cristiano Paris 18 Sep '09

18 Sep '09

I wish to thank Cafè's people for their great support in understanding Haskell. Thank you all! Cristiano

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Re: Where can I find a non-fee-based version of Hudak's paper, "Conception, evolution, and application of functional programming languages"?
by jean legrand 18 Sep '09

18 Sep '09

> Does anybody know where I can find a non-fee-based version of Paul > Hudak's paper, "Conception, evolution, and application of functional > programming languages" [1]? There used to be a version that did not seems you can get a djvu copy here http://lib.org.by/info/Cs_Computer science/CsPl_Programming languages/Hudak P. Conception, evolution, and application of functional programming languages (ACM comp.surveys 21, 1989)(T)(53s).djvu the site is in Russian and you wait 30s before a link to the file appears.

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About the parse error (possibly incorrect indentation)
by xu zhang 18 Sep '09

18 Sep '09

Hi, I am trying to get the function showMinProp to return String, but I always get an error of parse error (possibly incorrect indentation) Who can help with this? any idea? Thank u in advance! data Prop = Var String | Negation Prop | BinOp Op Prop Prop data Op = And | Or | Implies | Equiv derived Eq showOp :: Op -> String showOp And = "&" showOp Or = "|" showOp Implies = "=>" showOp Equiv = "<=>" instance Show Op where show = showOp precList = [(And,4),(Or,3),(Implies,2),(Equiv,1)] showProp :: Prop -> String showProp (Var s) = s showProp (Negation p) = "~" ++ showProp p showProp (BinOp op p q) = paren (showProp a p ++ space (showOp op) ++ showProp a q) showMinProp :: Int -> Prop -> String showMinProp preNo (BinOp op p q) = case op of And -> let a = 4 Or -> let a = 3 Implies -> let a = 2 Equiv -> let a = 1 if (a > preNo) then (showMinProp a p ++ space (showOp op) ++ showMinProp a q) else paren (showMinProp a p ++ space (showOp op) ++ showMinProp a q)) space s = " " ++ s ++ " " paren s = "(" ++ s ++ ")" instance Show Prop where show = showProp

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Where can I find a non-fee-based version of Hudak's paper, "Conception, evolution, and application of functional programming languages"?
by Benjamin L.Russell 18 Sep '09

18 Sep '09

Does anybody know where I can find a non-fee-based version of Paul Hudak's paper, "Conception, evolution, and application of functional programming languages" [1]? There used to be a version that did not require an ACM account available at http://www.cs.berkeley.edu/~jcondit/pl-prelim/hudak89functional.pdf , but when I try to download that file, the following error message appears: >The server has encountered a problem because access is restricted. > >Your request was : > http://www.cs.berkeley.edu/~jcondit/pl-prelim/hudak89functional.pdf -- Benjamin L. Russell [1] Hudak, Paul. "Conception, Evolution and Application of Functional Programming Languages." New York, NY: _ACM Computing Surveys (CSUR)_ 21(3) (September 1989): 359-411. <http://portal.acm.org/citation.cfm?id=72551.72554&coll=ACM&dl=ACM&idx=J204&…>. Also available at <http://www.cs.berkeley.edu/~jcondit/pl-prelim/hudak89functional.pdf>. -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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How to understand the 'forall' ?
by zaxis 18 Sep '09

18 Sep '09

data Branch tok st a = forall b. Branch (PermParser tok st (b -> a)) (GenParser tok st b) please shed a light on me, thanks! -- View this message in context: http://www.nabble.com/How-to-understand-the-%27forall%27---tp25250783p25250… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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help with FFI
by José Prous 17 Sep '09

17 Sep '09

Hello Lets say I have a library in C with a header like this: #include <stdio.h> /*really big structure*/ typedef struct { int *a; int *b; /*lots of stuff ... */ int *z; } foo; /*this function allocate memory and fill the structure, reading from a file*/ int create_foo(foo *f,FILE *file,int x,int y); /*some functions that use the structure*/ int use_foo(foo *f,int w); /*a funtion that releases the memory*/ int destroy_foo(foo *f); And I want to use it in haskell using FFI. I can create a .hsc file like this: {-# LANGUAGE CPP, ForeignFunctionInterface #-} import Foreign import Foreign.C.Types #include "foo.h" newtype Foo = Foo () foreign import ccall "static foo.h create_foo" c_create_foo :: Ptr (Foo) -> Ptr (CFile) -> CInt -> CInt -> IO CInt foreign import ccall "static foo.h use_foo" c_use_foo :: Ptr (Foo) -> CInt -> IO CInt foreign import ccall "static foo.h destroy_foo" c_destroy_foo :: Ptr (Foo) -> IO CInt It compiles but I have no idea how to call c_create_foo and get back Foo Any suggestions? thanks

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ANN: Unification in a Commutative Monoid (cmu 1.1) and a new release of Abelian group unification and matching (agum 2.2)
by John D. Ramsdell 17 Sep '09

17 Sep '09

Package cmu 1.1 provides unification in a commutative monoid, also know as ACU-unification. The core computation finds the minimal non-zero solutions to homogeneous linear Diaphantine equations. The linear equation solver has been place in a separate module so it can be used for other applications Package agum 2.2 provides unification and matching in an Abelian group, also know as AG-unification and matching. The core computation finds the integer solutions to inhomogeneous linear equations. The linear equation solver has been place in a separate module so it can be used for other applications John

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matching types in Haskell
by pat browne 17 Sep '09

17 Sep '09

Hi, I wish to align or match some Haskell types in order to represent a set of ontologies and their embedded concpts [1]. I am not sure wheather modules or classes could be used. I have done this task in a language called Maude[2]. The code is below. I appreciate that Maude is not very popular so there is a brief description below. This diagram below represents the semantics of what I am trying to achive. I want to construct MERGEDONTOLOGY from ONTOLOGY1 and ONTOLOGY2 both of which are based on COMMON. MERGEDONTOLOGY { Woman, RiverBank, FinancialBank, HumanBeing} /\ /\ / \ / \ / \ / \ / \ / \ ONTOLOGY1 ONTOLOGY2 {Woman, Bank, Person} {Woman, Bank, Human} /\ /\ \ / \ / \ / \ / \ / \ / \ / {Woman , Person} COMMMON Each Maude module represents (below) a distinct ontology, each sort (or type in Haskell) represents a concept. This example includes both synonyms and homonyms. I want to align ONTOLOGY1 and ONTOLOGY2 w.r.t COMMON to produce MERGEDONTOLOGY. The details of the concepts are as follows. The Woman concept should be the same in all ontologies, there is only one Woman concept and it is named as such in each ontology. Hence there should be only one Woman.MERGEDONTOLOGY There is only one concept HumanBeing.MERGEDONTOLOGY, but there are 3 synonyms Human.ONTOLOGY2, Person.ONTOLOGY1, and Person.COMMON It would seem that Person.COMMON should be mapped (or renamed?) to Human.ONTOLOGY2 which in turn is renamed (or mapped) to HumanBeing.MERGEDONTOLOGY. The homonyms are Bank.ONTOLOGY1 and Bank.ONTOLOGY2 which should become distinct entities in RiverBank.MERGEDONTOLOGY and FinancialBank.MERGEDONTOLOGY My question is how should this be done in Haskell. Is there a classes only solution? Is ther a module only solution? Or do I need both? Regards, Pat ============================================= Brief description of Maude code In the Maude Language the module is the basic conceptual unit. Sorts are declared in modules Every line ends with a space dot. In this case each module is bracketed by fth .. endfth There are various types of mappings between modules. In this case I used renamings where the syntax is *( name_in_source_module to name_in_target_module....) The keyword protecting is a type of inport. The + symbol between the modules forms a new module that includes all the information in each of its arguments ============================== fth COMMON is sorts Woman Person . endfth fth ONTOLOGY1 is protecting COMMON . sorts Bank . endfth fth ONTOLOGY2 is protecting COMMON *( sort Person to Human) . sorts Bank . endfth fth MERGEDONTOLOGY is including (ONTOLOGY1 * (sort Bank to RiverBank,sort Person to HumanBeing)) + (ONTOLOGY2 * (sort Human to HumanBeing, sort Bank to FinancialBank)) . endfth with the command show all MERGEDONTOLOGY the system will produce the following module fth MERGEDONTOLOGY0 is sorts Woman HumanBeing FinancialBank RiverBank . endfth ================================ Reference [1]Shapes of Alignments Construction, Combination, and Computation by Oliver Kutz, Till Mossakowsk, and Mihai Codescu http://www.informatik.uni-bremen.de/~okutz/shapes.pdf [2] Informa tiom on Maude at: http://maude.cs.uiuc.edu/

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algebra/grammar/language for expressing time intervals
by Jeremy Shaw 17 Sep '09

17 Sep '09

Hello, I need some cron-like functionality for long running daemon written in Haskell. I want to be able to schedule an event to be run: 1. once, at a specific time 2. some regularly scheduled time I don't see an existing library to do this, so I am starting work on my own. The first issue I am looking at is how to specify time intervals. The primary example I have looked at is cron. Cron is pretty good, but I don't see a way to do something like, run a job every other Wednesday. I also want to be able to display the interval schedule to the user, allow them to modify it, and also save the schedule to disk and reload it. So this essentially means that the type for describing the intervals can not contain any functions. Does anyone know of a good language for describing intervals? I want to be able to express things like: - run every other wednesday - run at 15 minutes past the hour - run at 15 minutes past the hour every wednesday - run at 15 and 25 minutes past the hour between the hours of 2 and 6 AM. - run every weekday at 8AM unless it is a holiday (the list of holidays would be supplied). Basically, everything you can express with cron, and a bit more. Is there any existing languages/grammars/algebras for this that I should look at? thanks! - jeremy

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