- Haskell-Cafe - Haskell.org

Fast Paced Haskell Tutorial
by Paulo J. Matos 12 Oct '07

12 Oct '07

Hello all, I'm interested in a freely available fast paced haskell tutorial. By fast paced, I means I want something that goes through basic in a very fast pace, presents a couple of examples and then talks about more advanced features. A set of tutorials would be also good. References to these kind of tutorials would be great. Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK

3 2

Type Synonyms
by Tom Davies 11 Oct '07

11 Oct '07

Newbie question: I was wondering the other day if type synonyms might be more useful if they were more restricted, that is, with the definitions: type Foo = String type Bar = String foo :: Foo foo = "a foo" bar :: Bar bar = "a bar" x :: Foo -> ... x f b = ...only valid for Foo Strings... both 'x foo' and 'x bar' type check correctly. Wouldn't it be useful if Foo and Bar were both equivalent to String, but Foo and Bar were not equivalent themselves? For instance, if you are using Strings as properties of something and want to associate the type of the property with its value, without wrapping the String. Would this break a transitivity property of the type system? Am I just suffering from laziness?

5 5

Hugs, dotnet, C#...
by Peter Verswyvelen 11 Oct '07

11 Oct '07

In the (Win)Hugs documentation, I found "Only the ccall, stdcall and *dotnet *calling conventions are supported. All others are flagged as errors." However, I fail to find any more information on how to invoke dotnet methods. This might be really handy for me, as I'm very familiar with the dotnet framework. For example, yesterday I rewrote and extended a program that I wanted to develop in Haskell in just 3 hours using dotnet, while I spend weeks trying do this in Haskell. Of course, I'm a Haskell newbie and a dotnet expert, so this is not a fair comparison. However, I got a strange feeling, which I want to share with you :) First of all, it was a *horrible* experience to program C# again; I needed to type at least 3 times the amount of code, much of which was boilerplate code, and the code is not elegant. Haskell really changed my point of view on this; before I knew Haskell, I found C# (I'm talking C# 3.0 here) a really neat and nice language. On the other hand, the great Visual Studio IDE and Resharper addin made it at least 3 times faster to type, navigate, refactor, and debug the code... Somehow, I get things done really really really fast in C#, albeit in an "ugly" way. Once again, I just wish Haskell had such an IDE... And yes, I know of the existance of Visual Haskell, EclipseFP, Haskell Mode for Emacs (which I'm using), VIM, YI, but still, these do not compare with the experience I have when using Visual Studio/Resharper (or Eclipse or IntelliJ/IDEA for Java). But that might just be me of course... A slightly frustrated Peter ;-) BTW: I don't want to bring up the IDE discussion again, no really ;-)

4 6

symbol type?
by Michael Vanier 11 Oct '07

11 Oct '07

Is there an implementation of a symbol type in Haskell i.e. a string which has a constant-time comparison operation? Mike

8 11

Re: [Haskell] Abstract syntax representation
by Neil Mitchell 11 Oct '07

11 Oct '07

Hi In future questions like this are usually best directed to haskell-cafe, with haskell being left for annoucements. The standard "full haskell" representation is in Template Haskell (http://haskell.org/ghc/docs/latest/html/libraries/template-haskell/Language…) If you want to work on a reduced language then I recommend Yhc.Core (http://www-users.cs.york.ac.uk/~ndm/yhc/ - there is a link to the Yhc.Core paper on that page). Thanks Neil

1 0

ANNOUNCE: metaplug
by mad.one＠gmail.com 11 Oct '07

11 Oct '07

Hi, Recently I just decided to finish up and publish my library, metaplug: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/metaplug What is it? It's basically a very tiny GHC API wrapper for programs that want eval and plugin style functionality packaged in a basic library. The need for it spawned out of my GHC API investigations, and looking at it as an easy way to get pluggable apps across GHC releases (hs-plugins is somewhat fragile as it can break basically inbetween any release,) and with the oh-so-close ghc 6.8 release, I needed something for things like my IRC bot (which does hot-code swapping) that wanted plugin style facilities without the hassle of using the API explicitly or having dependencies on soon to break packages like hs-plugins. Right now, there is no haddock documentation (I'll add it and upload a new version when I have time) but it's simple enough to figure out how to use from the source code. Here's a quickie review: Metaplug: top level module, you only need import this Metaplug.Eval: exports one function, eval, which, well, does what it sounds like Metaplug.Initialize: exports two functions, initSession and initSession' which initialize a metaplug session. initSession' is for the case where you want to provide your own very customized DynFlags to GHC.newSession Metaplug.Loader: provides two functions, loadFiles and compileCall which load files into a session and compiles a dynamic to a function you can call. Metaplug.Types: simply provides the SessionMode and MetaSession types Metaplug.Packages: provides a very simple interface to query the package database for info, please note this has NOT been tested with Cabal 1.2.0 There're some example applications in the tests/ directory which show off how to use most of this stuff in a very simple manner. Check the README. There is one limitation to this, however. compileCall expects to compile a dynamic via GHC.dynCompileExpr; what this means is your resource must be monomorphic (for Typeable to work.) As of right now, the easiest way I can see to get around this is to simply define a datatype like such: data Plugin { rsrc :: ... -- your type here } deriving Typeable And then have the symbol you want to compile could be for example, plugin = Plugin { rsrc = dynmain } The application in tests/dynst/ provides a good example of this. If anybody knows a way around this or an easier way to approach it, I appreciate all feedback (unsafeCoerce# is an option but there's not a version of compileCall to support this as of right now. I might add it if it seems needed.) Any feedback appreciated. Thanks, Austin

1 0

help!!!! install HaskellDirect
by Sulema Rocha Betancur 10 Oct '07

10 Oct '07

Hello :) Someone knows like installing HDirect 1,2 in Windows XP with cygwin? , and that version of GHC is the one that uses???.Thank you for its collaboration!!!!!!!! Sule ;) _________________________________________________________________ News, entertainment and everything you care about at Live.com. Get it now! http://www.live.com/getstarted.aspx

1 0

help!!!! install HakellDirect
by Sulema Rocha Betancur 10 Oct '07

10 Oct '07

Hello :) Someone knows like installing HDirect 1,2 in Windows XP with cygwin? , and that version of GHC is the one that uses???.Thank you for its collaboration!!!!!!!! Sule ;) _________________________________________________________________ Invite your mail contacts to join your friends list with Windows Live Spaces. It's easy! http://spaces.live.com/spacesapi.aspx?wx_action=create&wx_url=/friends.aspx…

1 0

Manual constructor specialization
by Johan Tibell 10 Oct '07

10 Oct '07

I have a rope data type with the invariant that one of its data constructors can never appear as a leaf. module Data.Rope where import Data.Word (Word8) data Rope = Empty | Leaf | Node !Rope !Rope index :: Rope -> Int -> Word8 index Empty _ = error "empty" index Leaf _ = error "leaf" index (Node l r) n = index' l n where index' Leaf _ = error "leaf" index' (Node l r) n = index' l n I removed some of the actual details (Leafs have a ByteString member and Nodes have a length and a depth field). The point is that Empty can only appear at the top by construction (i.e. it's not possible to construct a rope that breaks this invariant using the exported API). If I understand compilation of case statements correctly they will compile into some if like construct that checks the constructor tag. This means that I would like that once we have established that the constructor is not Empty we could use a specialized function to traverse the tree without checking for Empty on each iteration. The above doesn't achieve this as GHC inserts an automatic error branch for Empty in index'. Perhaps one solution is to reorder the cases and remove index'? -- Johan

6 6

Re: [Haskell-cafe] ANNOUNCE: binary 0.4: high performance, pure binary parsing and serialisation
by Don Stewart 09 Oct '07

09 Oct '07

ketil: > Don Stewart <dons(a)galois.com> writes: > > > The main thing is porting to ghc 6.8 -- which means the new (*faster*) > > lazy bytestring representation, and the smp parallel quickcheck driver > > for the testsuite (it'll use N cores, watch the jobs migrate around). > > Binary 0.4 seems to require bytestring 0.9, the library formerly known > as fps. I just want to mention it, as most network resources (as > found by Google) only have discoverd fps 0.7, which is not going to > work. > > (Oh, and yes, it's at darcs.haskell.org/bytestring/ ) > > It'd be nice - since I know you're at it anyway :-) - if hackage/cabal > would have some support for backwards compatibility. I know GHC 6.8 > is the thing to get, but some of us still install what comes with our > distribution, so I hope 6.6.1 still will be supported. > Normally this is farily easy to do, with cabal configurations. (See bytestring's .cabal file for example). However, the binary internals changed in such a way that it wasn't worth preserving backwards buildability. Instead, you should use binary 0.3 with ghc 6.6 libs A released version of bytestring 0.9 will be on hackage shortly. -- Don

2 2