[Haskell-cafe] Re: Editorial error or something meaningful?
PR Stanley [EMAIL PROTECTED] writes: Hi taken from ch.8.3 in the Hutton book: Whereas return v always succeeds, the dual parser failure always fails regardless of the contents of the input string: The dual parser failure? It's a question of how you parse the phrase dual parser failure. The name of the parser is failure and it is the dual (roughly meaning opposite) of the parser return. -- Jón Fairbairn [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Editorial error or something meaningful?
Am Samstag, 1. Dezember 2007 07:18 schrieb PR Stanley: Hi taken from ch.8.3 in the Hutton book: Whereas return v always succeeds, the dual parser failure always fails regardless of the contents of the input string: The dual parser failure? Cheers, Paul The dual parser, failure, probably. Cheers, Daniel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Categories list in French (off-topic?)
On Nov 30, 2007 9:13 PM, Maurício [EMAIL PROTECTED] wrote: Nice tip. Do you know of a free news server that allows read and post for that group? http://groups.google.com/group/fr.sci.maths/topics?lnk=gschg ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] trouble building unix-2.2.0.0 on cygwin
hi, with the large number of just chatting messages on haskell-cafe, it is all too easy to miss problem reports here. you might have a better chance asking on more specific lists, eg. for ghc use, or library issues http://www.haskell.org/mailman/listinfo/glasgow-haskell-users http://www.haskell.org/mailman/listinfo/libraries 0) All work being done on cygwin. Version 6.8.1 of ghc. the standard build of ghc uses cygwin tools to build a no-cygwin ghc. in particular, ghc is not linked with the posix-emulation libraries of cygwin, nor does it use cygwin's compiler or linker. so, unless you've made a non-standard cygwin-linked ghc, the unix package is unlikely to build with that ghc. do you really need the unix package? a lot of general functionality is available in platform-independent haskell libraries, and some of the unix-package functionality is available in unix compatibility packages. 1) I ran runhaskell Setup.lhs configure and did a tail -f config.log in order to follow the config process. 2) Next I did the build runhaskell Setup.lhs build but there were many include files referenced in HsUnix.h that couldn't be found, e.g. sys/times.h, sys/resources.h, sys/wait.h, 3) I went back through the file config.log and all of the so-called missing include files had supposedly been found during the config process. 4) Next I went to c:/cygwin/usr/include/sys and found all of the so-called missing include files. I am trying to get my confidence level up with respect to the config/build/install (and along with darcs and haddock) process up high so I can make a significant contribution to the Haskell effort. please .. any help will be appreciated. it is quite possible to work with a no-cygwin ghc in a cygwin environment. the environment supplies the build tools that some haskell packages and tools need for configuration and build, then the no-cygwin ghc produces a no-cygwin executable (which can be run from cygwin, or as any other windows-only program). that is indeed the default setup for ghc development on windows, so darcs, haddock, etc. should work in it, apart from a few rough edges. helping to smooth those edges, where things that should work don't quite work on windows, would be a significant contribution, imho. ideally, all haskell tools should work on windows entirely without non-windows tools, and while that is not likely in the near future, many of them already do, and reducing unix-dependencies helps to make haskell easier to use for windows users (just as avoiding windows-dependencies ensures that unix users are not excluded!-). claus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Sequencing Parsers: a Simple Example
Hi (=) :: Parser a - Parser b - Parser b p = f = \inp - case p inp of [] - [] [(v, out)] - parse (f v) out based on a lot of guesswork, after the mess created by the OCR, I managed to get the above example to work syntactically but is it semantically correct? Thanks, Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Sequencing Parsers: a Simple Example
Hi (=) :: Parser a - Parser b - Parser b p = f = \inp - case p inp of [] - [] [(v, out)] - parse (f v) out based on a lot of guesswork, after the mess created by the OCR, I managed to get the above example to work syntactically but is it semantically correct? Thanks, Paul You probably want: (=) :: Parser a - (a - Parser b) - Parser b p = f = \inp - case parse p inp of [] - [] [(v,out)] - parse (f v) out Assuming that you're following Graham Hutton's book. Note that this definition won't actually compile; you probably need a Monad instance and a newtype to get this to work properly (see http://www.cs.nott.ac.uk/~gmh/Parsing.lhs for a working version of the same code). Shachaf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Sequencing Parsers: a Simple Example
PRS: (=) :: Parser a - Parser b - Parser b p = f = \inp - case p inp of [] - [] [(v, out)] - parse (f v) out You probably want: (=) :: Parser a - (a - Parser b) - Parser b p = f = \inp - case parse p inp of [] - [] [(v,out)] - parse (f v) out Assuming that you're following Graham Hutton's book. Note that this definition won't actually compile; you probably need a Monad instance and a newtype to get this to work properly (see http://www.cs.nott.ac.uk/~gmh/Parsing.lhs for a working version of the same code). PRS: That explains it then. [(v, out)] - parse (f v) out caused a type mismatch. Cheers, Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: Teach Yourself Gtk2Hs in 21 Hours
Hello All, The Gtk2Hs basics tutorial, based on the Tony Gale and Ian Main GTK+2.0 tutorial, is now available for review and comment. The TOC: 1. Introduction 2. Getting Started 3. Packing 3.1 Packing Widgets 3.2 Packing Demonstration Program 3.3 Packing Using Tables 4. Miscellaneous Widgets 4.1 The Button Widget 4.2 Adjustments, Scale and Range 4.3 Labels 4.4 Arrows and Tooltips 4.5 Dialogs, Stock Items and Progress Bars 4.6 Text Entries and Status Bars 4.7 Spin Buttons 5. Aggregated Widgets 5.1 Calendar 5.2 File Selection 5.3 Font and Color Selection 5.4 Notebook 6 Supporting Widgets 6.1 Scrolled Windows 6.2 Event Boxes and Button Boxes 6.3 The Layout Container 6.4 Paned Windows and Aspect Frames 7. Action Based Widgets 7.1 Menus and Toolbars 7.2 Popup Menus, Radio Actions and Toggle Actions This covers about half of Gtk2Hs (guesstimate) but (hopefully) most of what's needed for the run of the mill GUI. It's available or will be on http://darcs.haskell.org/gtk2hs/docs/tutorial/Tutorial_Port/ http://j-van-thiel.speedlinq.nl/gtk2hs/index.html Thanks to Alex Tarkovsky it's in XHTML and well structured for easy maintenance and adaptation. I hope a Gtk2Hs basics tutorial will help to popularize this large, powerful and sophisticated gui library for Haskell. Needless to say, please don't hesitate to comment and report errors. Regards, Hans van Thiel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Illegal type def
Should work with glasgow extensions (-fglasgow-exts). - Phil On Dec 1, 2007 6:43 PM, PR Stanley [EMAIL PROTECTED] wrote: Hi type assoc k v = [(k, v)] works beautifully and everything makes sense. type Assoc v = (Ord k) = [(k, v)] This doesn't work. Is there any wayof defining k as an element of type Ordinal. I could redefine k by putting Char or Int in its place. Why can't I be more general? Thanks, Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Illegal type def
On Dec 1, 2007, at 21:43 , PR Stanley wrote: Hi type assoc k v = [(k, v)] works beautifully and everything makes sense. type Assoc v = (Ord k) = [(k, v)] This doesn't work. Is there any wayof defining k as an element of type Ordinal. I could redefine k by putting Char or Int in its place. Why can't I be more general? Think of a type declaration as a macro which is expanded where it is used. With parentheses around it and any unresolved references foralled, because it has no idea what to do with them at declaration time. So, if you use -fglasgow-exts, you could make the above type declaration. But when you use it: foo :: Assoc Int - Assoc Int translates as foo :: (forall k. (Ord k) = [(k,Int)]) - (forall k. (Ord k) = [(k,Int)]) This is almost certainly *not* what you want; the two ks are independent. It could be argued that GHC should be smarter about it... but formalizing what that means is difficult (and subject to disagreements). -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Modelling a mutable variable store
I'm implementing an interpreter for the lambda calculus augmented with mutable variables. I'm having problems doing the mutable state stuff in Haskell. Here's what I have so far: type Expr= ... terms in the language ... type Value = ... values in the language ... type Ident = String type VarId = String type Env = Map Ident Target data Target = TValue Value | TVar VarId -- idents might refer to values or vars in the store. type Store = Map VarId (Maybe Value) -- Using Maybe because vars start out uninitialized. eval :: (Env, Store, Expr) - (Store, Value) -- The Store is threaded through the evaluator. One problem is that the link between an identifier and it's entry in the store is via VarIds, which are just strings. For example, if I see the identifier x, I first look it up in the Env, and if it is a TVar, I then look it up in the store. I'd like to get something stronger (in Java, I would use a pointer). Another problem is that entries in my Store never get garbage collected. Again, if I were using pointers in Java, this wouldn't be an issue. There's also the issue of finding a more elegant way of threading the Store through my evaluator, but I'm not concerned too much about that at this point. I can probably define a state-carrying monad like Parsec. My real concerns are the first two issues. Thanks. - Kannan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Modelling a mutable variable store
On Sun, 2007-12-02 at 03:29 +, Robin Green wrote: On Sat, 01 Dec 2007 21:22:53 -0600 Derek Elkins [EMAIL PROTECTED] wrote: There's also the issue of finding a more elegant way of threading the Store through my evaluator, but I'm not concerned too much about that at this point. I can probably define a state-carrying monad like Parsec. My real concerns are the first two issues. Use ST. First-class state isn't too great unless you specifically want that. Or use IO - that way you can use a Hashtable for looking up identifiers. Although, better still is to convert variable references into Ints, instead of using a Hashtable. From what I hear, Data.HashTable is impressively inefficient to the extent that you're better off using Data.Map solely for performance (not to mention it being pure.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Modelling a mutable variable store
On Sat, 01 Dec 2007 21:22:53 -0600, Derek Elkins wrote: Use ST. First-class state isn't too great unless you specifically want that. I did try using ST but ran into a problem because its type variable (s) ended up invading all of my types. -- Target needs 's' because of the STRef data Target s = TValue Value | TVar (STRef s (Maybe Value)) -- Env needs 's' because Target needs 's' type Env s = Map Ident (Target s) -- Value needs 's' because closures are values and closures -- have an Env. data Value s = VUnit | VClosure (Env s) Ident Expr The main thing I didn't like was that 'Value' had a type parameter. I didn't follow the ST option much past this point. But maybe there's a better way to use ST? Will existential types help me? - Kannan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Modelling a mutable variable store
On Sun, Dec 02, 2007 at 03:54:05AM +, Kannan Goundan wrote: On Sat, 01 Dec 2007 21:22:53 -0600, Derek Elkins wrote: Use ST. First-class state isn't too great unless you specifically want that. I did try using ST but ran into a problem because its type variable (s) ended up invading all of my types. That's just ST ugliness, the price you have to pay for a pure runST. If you're doing almost everything in ST, it can be cleaner just to use IORefs. Stefan signature.asc Description: Digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell interface file (.hi) format?
On Fri, Nov 30, 2007 at 08:55:51AM +, Neil Mitchell wrote: Hi Prelude :b Control.Concurrent.MVar module 'Control.Concurrent.MVar' is not interpreted :b now defaults to :breakpoint, you want :browse That's a questionable decision, IMO: - it changes behavior - I expect :browse to be used more often, so it deserves the sort :b version (:bro is not that short) On the other hand, this change can have an (unintended?) feature advertising effect ;-) Best regards Tomasz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell interface file (.hi) format?
On Sun, Dec 02, 2007 at 05:45:48AM +0100, Tomasz Zielonka wrote: On Fri, Nov 30, 2007 at 08:55:51AM +, Neil Mitchell wrote: Hi Prelude :b Control.Concurrent.MVar module 'Control.Concurrent.MVar' is not interpreted :b now defaults to :breakpoint, you want :browse That's a questionable decision, IMO: - it changes behavior - I expect :browse to be used more often, so it deserves the sort :b version (:bro is not that short) On the other hand, this change can have an (unintended?) feature advertising effect ;-) It's not a decision at all. :b is the first command starting with b, which was browse yesterday, is breakpoint today, and tomorrow will be something you've never heard of. It's inherently fragile, and shouldn't be relied on in scripts - and if :b does anything funny, spell out the command! (There is a case to be made for explicitly defining short forms of commands - but that is not what :b is, and making this case should only be done in a new thread.) Stefan signature.asc Description: Digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell interface file (.hi) format?
On Sat, Dec 01, 2007 at 10:01:13PM -0800, Stefan O'Rear wrote: On Sun, Dec 02, 2007 at 05:45:48AM +0100, Tomasz Zielonka wrote: That's a questionable decision, IMO: - it changes behavior - I expect :browse to be used more often, so it deserves the sort :b version (:bro is not that short) On the other hand, this change can have an (unintended?) feature advertising effect ;-) It's not a decision at all. :b is the first command starting with b, which was browse yesterday, is breakpoint today, and tomorrow will be something you've never heard of. I haven't thought about it this way. OK, so _this_ is the questionable decision: allowing the ambiguous shortcut. It's inherently fragile, and shouldn't be relied on in scripts I am only relying on it in my brain's procedural memory and I guess it's going to fix itself eventually ;-) Best regards Tomasz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
