- Haskell-Cafe - Haskell.org

more haskeem: it's just scheme in haskell now, no more "almost"
by Uwe Hollerbach 03 Feb '08

03 Feb '08

Hello, haskellers, my mud pies are getting bigger: I have added an exception-handling mechanism to haskeem (ie, for handling exceptions at the scheme level, not the haskell level; that was already working), and also hooked up the REPL to gnu readline: the example code for the readline command was practically tailor-made for me! :-) Also, I must apologize: I screwed up the URL earlier: I had said http://www.korgwal.com/software/haskeem/ and then promptly went and stuck it into http://www.korgwal.com/haskeem/ ... you may attribute that to rapidly-advancing senility, if you like, I won't contradict you. Anyway, I've fixed it by simply putting copies into both places. regards, Uwe Hollerbach

2 1

hdbc, Oracle, and Solaris
by Daniil Elovkov 03 Feb '08

03 Feb '08

Hello folks. I don't understand whether hdbc has a specific Oracle backend or not (not via odbc). It is listed in the description of hdbc, but not really found elsewhere, it seems. I'd like to have a non-odbc support because it is very desirable to have it working on Solaris, and I'm not sure if it will be easy to set it up with odbc there. So, the question might go: has somebody had success with native Oracle support on Solaris with hdbc? Well, or hsql?

1 0

Yi, or Gtk2hs or fedora rpm problem?
by Jon Fairbairn 03 Feb '08

03 Feb '08

This was mentioned on the yi-devel list <http://groups.google.com/group/yi-devel/browse_frm/thread/392c3cd612490b1a/…> but didn't cause much excitement as it's not clear whose problem it is, so I'll ask here as well: I recently downloaded yi-0.3 and tried to build it, but get Loading package base ... linking ... done. Loading package array-0.1.0.0 ... linking ... done. Loading package bytestring-0.9.0.1 ... linking ... done. Loading package regex-base-0.72.0.1 ... linking ... done. Loading package regex-posix-0.72.0.2 ... linking ... done. Loading package regex-compat-0.71.0.1 ... linking ... done. Loading package fingertree-0.0 ... linking ... done. Loading package mtl-1.1.0.0 ... linking ... done. Loading package glib-0.9.12.1 ... linking ... done. Loading package cairo-0.9.12.1 ... linking ... done. yi: /usr/lib/ghc/6.8.2/gtk2hs/HSgtk.o: unknown symbol `containerszm0zi1zi0zi1_DataziSequence_length_info' Loading package gtk-0.9.12.1 ... linking ... yi: exception :: GhcException for any attempted invocation of yi. I don't know whether this problem is specific to yi, to gtk2hs or to the fedora 8 rpm of gtk2hs or something else (ghc 6.8.2). I tried to rpm --rebuild the gtk2hs source rpm, but the build failed, complaining of missing documentation files (the spec file can't be right, or I'd have seen an unsatisfied build-dependency message instead). What's the next step? -- Jón Fairbairn Jon.Fairbairn(a)cl.cam.ac.uk

1 0

SPJ on the radio (at .NET Rocks :)
by Don Stewart 03 Feb '08

03 Feb '08

Simon talks about laziness, purity and other FP concepts to some .NET guys. Simon starts 7minutes 20seconds in. http://www.dotnetrocks.com/default.aspx?ShowNum=310 Good work Simon! -- Don

3 2

ANN: Hlist 0.1 on Hackage
by gwern0＠gmail.com 03 Feb '08

03 Feb '08

Hey everyone: I'd like to make a short announcement that with the permission of its maintainer, I've uploaded HList v0.1 to Hackage. You can find the Hackage page here: <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HList-0.1>. 'cabal install HList' should also work. HList for those who don't know is a sort of OO Haskell package which permits heterogeneous lists; you can find out more at <http://homepages.cwi.nl/~ralf/HList/>. (The Darcs repository is at <http://darcs.haskell.org/HList>.) What changes have been made to the darcs repo? Well, they are mostly updates and cleanups - I've updated build-depends for GHC 6.8.x; largely moved from -fglasgow-exts to LANGUAGE pragmas; put the modules in a proper module namespace; fixed up Haddock generation; removed some unused files, and other things of that nature. -- gwern Covert data bank Armani Larson Missiles Dick CTP SO13 AUTODIN

1 0

Refactoring from State monad to ST monad, for STUArray
by Denis Bueno 03 Feb '08

03 Feb '08

Is it possible to use the ST monad as a (drop-in) replacement for the State monad in the following situation? If not, is there a "best practice" for refactoring? I have a bunch of functions that return state actions: type MyState = ... foo1 :: T1 -> State MyState a foo2 :: T2 -> State MyState a ... foon :: Tn -> State MyState a And I'd like to refactor this to use the ST monad, mechanically, if possible. All uses of the MyState inside State are single-threaded. In my application, MyState is a record with 5 or so fields. One of those fields uses a list to keep track of some information, and I'd like to change that to STUArray, because it changes my bottleneck operations from O(n) to O(1). This, of course, requires having the ST monad around, in order to achieve the proper time complexity. Is there an easy way to do this? In the future, should I *start out* with the ST monad if I suspect I'll need to use an imperative data structure for efficiency reasons? I started out with State because I'm modeling a transition system, so it seemed natural. Any advice is appreciated. -- Denis

4 6

strange GHC assembler failure
by Tim Newsham 03 Feb '08

03 Feb '08

I'm getting a weird build error: [ 9 of 95] Compiling Plugin.Pl.Common ( Plugin/Pl/Common.hs, dist/build/lambdabot/lambdabot-tmp/Plugin/Pl/Common.o ) /tmp/ghc52608_0/ghc52608_0.s: Assembler messages: /tmp/ghc52608_0/ghc52608_0.s:36:0: Error: unassigned file number 1 [... more of these ...] I narrowed this down -- this happens when I add my new library "silc-client" to the "Build-depends:" line in the cabal file even if none of its code is referenced. Removing the dependency makes the error go away. The module I'm referencing is a new one I'm still working on and it makes use of FFI and references external headers and libraries. (I put a copy at http://www.thenewsh.com/~newsham/silc-client.tgz if it helps anyone debug.. this is not release-quality code though). Any idea what is going on here? Tim Newsham http://www.thenewsh.com/~newsham/

1 0

Re: [Haskell-cafe] Circular enums
by Ben Butler-Cole 03 Feb '08

03 Feb '08

On Feb 2, 2008, at 18:41 , I wrote: > No instance for (Bounded a) > arising from use of `maxBound' at Hbot.hs:6:34-41 > (...) > My (clearly flawed) understanding of the signature I've specified > for 'turn' means *exactly* that a is Bounded. Brandon Allbery replied: > The problem is that the scope of a is the type signature; it does > *not* extend to the definition. > > You can try omitting the type on maxBound and minBound, or you > can enable the scoped type variables extension Thank you. This compiles fine with the Glasgow extensions turned on as long as the type in the function signature is universally quantified: turn :: forall a. (Enum a, Bounded a) => Int -> a -> a turn n e = toEnum (add (fromEnum (maxBound::a) + 1) (fromEnum e) n) where add mod x y = (x + y + mod) `rem` mod

1 0

Circular enums
by Ben Butler-Cole 02 Feb '08

02 Feb '08

Hello I'm trying to define functions that allow you to traverse a bounded enumeration, "wrapping" at the start and the end. My implementation looks like this: next, prev :: (Enum a, Bounded a) => a -> a next = turn 1 prev = turn (-1) turn :: (Enum a, Bounded a) => Int -> a -> a turn n e = toEnum (add (fromEnum (maxBound::a) + 1) (fromEnum e) n) where add mod x y = (x + y + mod) `rem` mod Which fails to type check under GHC with this error: No instance for (Bounded a) arising from use of `maxBound' at Hbot.hs:6:34-41 Probable fix: add (Bounded a) to the expected type of an expression In the expression: maxBound :: a In the first argument of `fromEnum', namely `(maxBound :: a)' In the first argument of `(+)', namely `fromEnum (maxBound :: a)' My (clearly flawed) understanding of the signature I've specified for 'turn' means *exactly* that a is Bounded. Can anyone enlighten me as to where my understanding is going awry and how (whether) I can achieve what I'm trying to do. Thank you Ben

2 1

Circular enums - resend
by Ben Butler-Cole 02 Feb '08

02 Feb '08

[Resending with formatting fixed.] Hello I'm trying to define functions that allow you to traverse a bounded enumeration, "wrapping" at the start and the end. My implementation looks like this: next, prev :: (Enum a, Bounded a) => a -> a next = turn 1 prev = turn (-1) turn :: (Enum a, Bounded a) => Int -> a -> a turn n e = toEnum (add (fromEnum (maxBound::a) + 1) (fromEnum e) n) where add mod x y = (x + y + mod) `rem` mod Which fails to type check under GHC with this error: No instance for (Bounded a) arising from use of `maxBound' at Hbot.hs:6:34-41 Probable fix: add (Bounded a) to the expected type of an expression In the expression: maxBound :: a In the first argument of `fromEnum', namely `(maxBound :: a)' In the first argument of `(+)', namely `fromEnum (maxBound :: a)' My (clearly flawed) understanding of the signature I've specified for 'turn' means *exactly* that a is Bounded. Can anyone enlighten me as to where my understanding is going awry and how (whether) I can achieve what I'm trying to do. Thank you Ben

1 0