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Converting image2PS function
by iliali16 18 Mar '08

18 Mar '08

Hi guys again just want to ask you I have this function ready -- Creates a Postscript file from an Image -- page shows -200 <= x <= 200, 300 <= y <= 300 -- boundaries, plus origin plotted on output image2PS:: Image -> String -> IO() image2PS (Image contents) filename = writeFile filename (header++contents++footer) where header = unlines ["%!PS-Adobe-3.1" ,"%%BoundingBox: 100 125 500 725" ,"%%PageOrder: Ascend" ,"%%Pages: 1" ,"%%BeginDocument" ,"%%Page: 1 1" ,"100 125 moveto 500 125 lineto 500 725 lineto 100 725 lineto closepath gsave stroke grestore clip" ,"275 425 moveto 50 0 rlineto stroke" ,"300 400 moveto 0 50 rlineto stroke" ] footer = unlines ["showpage" ,"%%EndDocument" ] but when I use it for example image2PS spiral iliali it tells me that the iliali is undefined. What do you thing how should I use it. Thanks in advance! PS: I need to know how this works so that I make a similar function that converts logo2PS since I have a Logo spiral and I want to see it in PostScript. Thanks again! -- View this message in context: http://www.nabble.com/Converting-image2PS-function-tp16122095p16122095.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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build recent(ish) ghc on macos 10.3.9 powerpc?
by Uwe Hollerbach 18 Mar '08

18 Mar '08

[Augh! gmail won't send! Apologies if this shows up more than once...] Hi, all, I have an old iMac G3, running OSX 10.3.9, to which I have a sentimental attachment. I'd like to get ghc running on it, but the pre-built binaries I can find are all for more-recent iMacs, so I thought I would try to build it myself. I believe I read somewhere that gcc 3.3.X didn't work quite right for recent ghc -- I'm trying for now to build ghc 6.6.1 -- so I started by upgrading gcc to 3.4.6. That's working. So, with that in place, I went to the "porting ghc to a new arch" page and started going through the steps. I'm using a laptop running linux as the "host" computer, so that's i386-unknown-linux, some Fedora core derivative. It's using gcc 3.4.4. I think I did all the initial stuff right, but in the section in the porting guide where it says to start diving into all the subdirectories and do a bunch of "make boot && make", I start getting errors, and by the time it says to do that in .../libraries, it just croaks. Did I miss something earlier? Is this a completely hopeless endeavor from the get-go? I'm not even sure what intermediate files or error messages I should post. Any hints appreciated!. If you want to tell me, "Uwe, you're a bozo", that's fine, too, and you could well be right, just tell me why... Thanks! Uwe

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Small question about something easy
by iliali16 18 Mar '08

18 Mar '08

Hi guys I am a bit new to haskell but I am doing good till now. I have to write a function that takes 2 inputs and then reutns one composite output. Now my problem is that I have to make composition of that function meaning that I have to access in some way the output of the function before it is really computed. I will show you part of my code which is working prefectly: play :: Logo -> TurtleState -> (Image, TurtleState) play DoNothing (pen, (x,y), angle) = (emptyImage, (pen, (x,y), angle)) play PenDown (pen, (x,y), angle) = (emptyImage,(pen, (x,y), angle)) play PenUp (pen, (x,y), angle) = (emptyImage,(pen, (x,y), angle)) play (Forward n) (pen, (x,y), angle) |pen == True = ((line (x,y) (x+n,y+n)), (True, (x+n,y+n), angle)) |otherwise = (emptyImage,(pen, (x+n,y+n), angle)) play (Turn n) (pen, (x,y), angle) = (emptyImage, (pen, (x,y), (angle+n))) play (DoNothing :>: p2) (pen, (x,y), angle) = play p2 (pen, (x,y), angle) play (p1 :> DoNothing) (pen, (x,y), angle) = play p1 (pen, (x,y), angle) play (PenDown :>: PenUp) (pen, (x,y), angle) = (emptyImage,(pen, (x,y), angle)) play (PenDown :>: (Forward n)) (pen, (x,y), angle) = play (Forward n) (True, (x,y), angle) play (PenDown :>: PenDown) (pen, (x,y), angle) = (emptyImage,(pen, (x,y), angle)) play (PenDown :>: (Turn n)) (pen, (x,y), angle) = play (Turn n) (pen, (x,y), angle) play (PenUp :>: PenUp) (pen, (x,y), angle) = (emptyImage,(pen, (x,y), angle)) play (PenUp :>: (Forward n)) (pen, (x,y), angle) = play (Forward n) (False, (x,y), angle) play (PenUp :>: (Turn n)) (pen, (x,y), angle) = play (Turn n) (pen, (x,y), angle) play (PenUp :>: PenDown) (pen, (x,y), angle) = (emptyImage,(pen, (x,y), angle)) Now the problem comes here: play (p1 :>: p2) state |play p1 state == (i1,state1) && play p2 state1 == (i2,state2) = (i1+++i2,state2) I know that if I manage to do that function the one above with this sign :>: do not need to be impelmented since this one will cater for all the cases. Can you please help me? Thanks in advance! -- View this message in context: http://www.nabble.com/Small-question-about-something-easy-tp16119618p161196… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Need Cabal/library building help for windows
by Ryan Ingram 18 Mar '08

18 Mar '08

For reference, I'm using GHC6.8.1 on WinXP. I'm trying to package up some code into a library. But cabal fails to configure my project: >runhaskell setup.hs configure Configuring Prompt-1.0... setup.hs: ld is required but it could not be found. Prompt.cabal contains: name: Prompt version: 1.0 cabal-version: >= 1.2 build-type: Simple library exposed-modules: Control.Monad.Prompt Does GHC require additional tools in order to build libraries on Win32? If so, I hope this can be remedied; it builds executables without additional tools after all. What do I need to do next? -- ryan

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haskell.org is accepted to GSoC
by Malcolm Wallace 18 Mar '08

18 Mar '08

Google announced last night that Haskell.org has been accepted as a mentoring organisation for this year's Summer of Code (amongst 175 Open Source organisations). http://code.google.com/soc/2008/ The game is on! Student applications open at 1900 UTC on Mon 24th March, and close at 2400 UTC on Mon 31st March. In the meantime, my _strong_ suggestion is for students to search for ideas amongst the many lists available on the web: http://hackage.haskell.org/trac/summer-of-code/ http://haskell.org/haskellwiki/Hac_2007_II/Projects http://haskell.org/haskellwiki/Hac4/Projects and when crafting your proposal: * post it to an appropriate mailing list for comments e.g. haskell-cafe, libraries, wxHaskell, cabal-devel (prefix your subject line with [GSoC] to make it easy to find) * use feedback from the list to improve your proposal. Potential mentors will rank your final submitted proposal based on your ability and commitment to engage with the wider Haskell community, in addition to technical merit. Proposals that will benefit the entire Haskell world will generally be ranked more highly than niche projects with only a few potential users. So things like Cabal-hacking, darcs-hacking, compiler-hacking, are good, as are new libraries to do tasks that are in high demand. (This is not an exhaustive list.) Regards, Malcolm

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ANN: haskell-src-exts 0.3.2
by Niklas Broberg 18 Mar '08

18 Mar '08

Hi all, I'm pleased to announce a new release for the haskell-src-exts package. haskell-src-exts 0.3.2 =========================== haskell-src-exts is a package for handling and manipulating Haskell source code. It is based on the haskell-src package that is part of the standard libraries, but extends this to support a number of syntactic extensions, e.g. MPTCs, fundeps, GADTs, TH etc. It is intended as a drop-in replacement for the standard haskell-src package, and exports the same functions and data types, plus some more. Apart from the more standard extensions supported by e.g. GHC, haskell-src-exts also provides support for HaRP (Haskell Regular Patterns) and HSX (Haskell Source with XML) syntax. Note that as of 0.3, haskell-src-exts /= HSX. * cabal sdist: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts… * darcs repo: darcs get http://code.haskell.org/HSP/haskell-src-exts === Changes from 0.2: === * Added support for - Indexed type families (including associated types/datatypes) - Explicit kind signatures - Standalone deriving * haskell-src-exts is now decoupled from hsx/trhsx and harp. - Modules renamed to Language.Haskell.Exts.* - Module Transform is removed from the package (now in package hsx) * New repository (i.e. darcs pull in an old repo won't work, use darcs get), containing only the haskell-src-exts package (no hsx or harp). * Builds with 6.8.2 (thanks Duncan Coutts) === Complete list of supported extensions === * Multi-parameter type classes (MPTCs) * Functional dependencies * Associated types, indexed type families * Liberal class and instance heads * Implicit parameters * Explicit kind signatures * Pattern guards * Generalized algebraic data types (GADTs) * Template Haskell (TH) * Universal and existential quantification (forall) * Empty data type declarations * Unboxed tuples (# #) * Standalone deriving * Regular patterns * Haskell XML, HSX style === Build Requirements === * happy >= 1.17 - It might work with 1.16 though I haven't tested. In that case change the cabal file. - It would work with older versions as well, though they insert a dependency on Array (haskell98) instead of Data.Array. If that's all you have to work with, update the cabal file with a dependency on haskell98. * Cabal >= 1.2 Patches are more than welcome. :-) Cheers, /Niklas

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Haskell board game, anyone?
by Benjamin L. Russell 18 Mar '08

18 Mar '08

Maybe off topic, but when I saw this, I thought, "Why isn't there a Haskell version of this game?" (Or is there?) C-jump is a neat idea, mapping something fun (downhill skiing) with programming. I look at this game and wonder what it would look like in the wonderful world of higher-order functions. Begin forwarded message from "Geoff Knauth" (with subject "[plt-scheme] Scheme board game, anyone?" on "PLT-list Mailing List" <plt-scheme(a)list.cs.brown.edu>, dated "Mon, 17 Mar 2008 12:38:32 -0400"): > Maybe off topic, but when I saw this, I thought, "Why > isn't there a > Scheme version of this game?" (Or is there?) > > C-jump is a neat idea, mapping something fun (downhill > skiing) with programming. I look at this game and > wonder what it would look like > in the wonderful world of continuations. > > Begin forwarded message from Chase Turner: > > > Subject: Is there a Scheme version of this game? > > > > http://www.c-jump.com Benjamin L. Russell

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problem with type equality constraints
by Ganesh Sittampalam 18 Mar '08

18 Mar '08

Hi, When I try to compile this code with ghc-6.9.20080310: module Test2 where type family Id a type instance Id Int = Int type instance Id (a, b) = (Id a, Id b) class Id a ~ ida => Foo a ida instance Foo Int Int instance (Foo a ida, Foo b idb) => Foo (a, b) (ida, idb) I get these errors: Test2.hs:12:0: Couldn't match expected type `ida' against inferred type `Id a' `ida' is a rigid type variable bound by the instance declaration at Test2.hs:12:16 When checking the super-classes of an instance declaration In the instance declaration for `Foo (a, b) (ida, idb)' Test2.hs:12:0: Couldn't match expected type `idb' against inferred type `Id b' `idb' is a rigid type variable bound by the instance declaration at Test2.hs:12:27 When checking the super-classes of an instance declaration In the instance declaration for `Foo (a, b) (ida, idb)' It seems to me that since Foo a ida and Foo b idb are superclassess, Id a ~ ida and Id b ~ idb should be known and so this should have worked - am I missing something? Cheers, Ganesh

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Network.Browser and getCookies
by Adam Smyczek 18 Mar '08

18 Mar '08

Somehow I cannot get cookies from the Response using Network.Browser module (HTTP 3001.0.4). The cookie header part seams to be empty and getCookies returns empty list as well. Any idea how to debug this or does someone have a working example? Thanks, Adam

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2-level type analysis of introducing naming into data types
by Greg Meredith 17 Mar '08

17 Mar '08

All, The following Haskell code gives a 2-level type analysis of a functorial approach to introducing naming and name management into a given (recursive) data type. The analysis is performed by means of an example (the type of Conway games). The type is naturally motivated because through the application of one functor we arrive at a lambda calculus with an embedded type for Conway games (giving access to field operations for arithmetic on virtually every type of number ever considered) -- while another functor provides a process calculi with a similarly embedded data type. Moreover, the technique extends to a wide variety of algebra(ic data type)s. The recipe is simple. 1. Provide a recursive specification of the algebra. Example. data Game = Game [Game] [Game] 2. Abstract the specification using parametric polymorphism. Example. data PolyGame g = PolyGame [g] [g] 2.a. Identify the 2-Level knot-tying version of the recursive type Example. data RGame = RGame (PolyGame RGame) 3. Insert name management type into the knot-tying step of the 2-Level version Example. data DefRefGame var = DefRefGame (PolyDefRef var (PolyGame (DefRefGame var))) given the basic form data PolyDefRef var val = Def var (PolyDefRef var val) (PolyDefRef var val) | Ref var | Val val is the name management technology We illustrate the idea with two other forms of name management technology: the lambda calculus and the pi-calculus. Then we show that names themselves can be provided as the codes of the terms of the new type. At the root of this work is the proposal that communication begins from the concrete -- a "closed" recursive type -- representing some observation or proposal of how something works in the universe (of discourse). As said proposal develops or is explored, calculations need to rely more and more on naming (i.e. "let x stand for ... in ..."). Thus, this capability is "injected" into the data type -- moving from the concrete to the general. The analysis above provides a concrete, disciplined procedure for achieving this in both a sequential and concurrent computational setting. Best wishes, --greg -- This code summarizes the previous post. It shows that for any -- "closed" recursive type we can devise a closed extension of this -- type embedding the type as a value in the lambda calculus module Grho( Game, PolyGame, PolyDefRef, DefRefGame, QDefRefGame ,Term, GTerm, QGTerm ,Sum, Agent, Process, GProcess, QGProcess ) where -- Conway's original data type data Game = Game [Game] [Game] deriving (Eq,Show) -- Abstracting Conway's data type data PolyGame g = PolyGame [g] [g] deriving (Eq,Show) -- Recovering Conway's data type in terms of the abstraction newtype RGame = RGame (PolyGame RGame) deriving (Eq,Show) -- RGame ~ Game -- Expressions with references and values data PolyDefRef var val = Def var (PolyDefRef var val) (PolyDefRef var val) | Ref var | Val val deriving (Eq,Show) -- Games with references and values data DefRefGame var = DefRefGame (PolyDefRef var (PolyGame (DefRefGame var))) deriving (Eq,Show) -- Games with references and values in which variables are quoted games newtype QDefRefGame = QDefRefGame (DefRefGame QDefRefGame) deriving (Eq,Show) -- Lambda terms with values data Term var val = Var var | Abs [var] (Term var val) | App (Term var val) [Term var val] | Value val deriving (Eq,Show) -- Lambda terms with games as values data GTerm var = Term var (PolyGame (GTerm var)) deriving (Eq,Show) -- Lambda terms with games as values and variables that are quoted lambda terms data QGTerm = GTerm QGTerm -- And the following defn's/eqns take it one step further by providing a notion of process with -- Conway games as embedded values -- Process terms with values -- Sums data Sum var val agent = PValue val | Locate var agent | Sum [Sum var val agent] deriving (Eq,Show) -- One of the recent observations i've had about the process calculi -- is that '0' is Ground, and as such is another place to introduce -- new Ground. Thus, we can remove the production for '0' and replace -- it with the types of values we would like processes to 'produce'; -- hence the PValue arm of the type, Sum, above. Note that this -- design choice means that we can have expressions of the form -- v1 + v2 + ... + vk + x1A1 + ... xnAn -- i am inclined to treat this as structurally equivalent to -- x1A1 + ... xnAn -- but there is another alternative: to allow -- sums of values to represent superpositions -- Agents data Agent var proc = Input [var] proc | Output [proc] deriving (Eq,Show) -- Processes data Process var sum = Case sum | Deref var | Compose [Process var sum] deriving (Eq,Show) -- Processes over games data GProcess var = Process var (Sum var (PolyGame (GProcess var)) (Agent var (GProcess var))) deriving (Eq,Show) -- Processes over games with quoted process for variables newtype QGProcess = QGProcess (GProcess QGProcess) deriving (Eq,Show) -- L.G. Meredith Managing Partner Biosimilarity LLC 806 55th St NE Seattle, WA 98105 +1 206.650.3740 http://biosimilarity.blogspot.com

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