- Haskell-Cafe - Haskell.org

haddock-2.3.0 literate comments discarded from .lhs input
by Alistair Bayley 09 Feb '09

09 Feb '09

I have this test case for Haddock (2.3.0): -------------------------------------------------- | Module : Test.Haddock Copyright : (c) 2009 Alistair Bayley License : BSD-style Maintainer : alistair(a)abayley.org Stability : stable Portability : portable Test case for Haddock. > module Test.Haddock > ( > -- $named_block > Fail(..) > ) > where > data Fail = Fail | Succeed $named_block This is some hadock documentation. -------------------------------------------------- This fails with: [1 of 1] Compiling Test.Fail ( Test\Fail.hs, Test\Fail.o ) Test\Fail.hs:11:26: Can't make a derived instance of `Typeable Fail' (You need -XDeriveDataTypeable to derive an instance for this class) In the data type declaration for `Fail' If I manually unlit, then Haddock is happy: -------------------------------------------------- -- | -- Module : Test.Haddock2 -- Copyright : (c) 2009 Alistair Bayley -- License : BSD-style -- Maintainer : alistair(a)abayley.org -- Stability : stable -- Portability : portable -- -- Test case for Haddock. module Test.Haddock2 ( -- $named_block Fail(..) ) where data Fail = Fail | Succeed -- $named_block -- -- This is some hadock documentation. -------------------------------------------------- so it looks as though it's discarding the literate comments. Is this intended? I was under the impression that because it used the ghc parser, it could now properly handle .lhs input. Ona related note, we have a nice unlitter in cabal that would preserve these comments before invoking haddock. Is this still used with haddock2, or does it now assume haddock2 will do the right thing? Alistair

4 7

ANNOUNCE: X Haskell Bindings 0.1
by Antoine Latter 08 Feb '09

08 Feb '09

I'd like to announce a version bump for the X Haskell Bindings (XHB) library, to 0.1.* from 0.0.*. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the X protocol C-language Binding (XCB). On Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb This release focuses on making the API a bit friendlier: + 'type BOOL = Word8' has been replaced in the API by Prelude.Bool + type synonyms BYTE, CARD8, CARD16 and CARD32 for the Data.Word types have been eliminated + type synonyms INT8, INT16 and INT32 for the Data.Int types have been eliminated + Previously, all protocol replies were represented by their own distinct data type. Now, if the reply to a request only includes a single field, the request returns that field directly. In more concrete terms: > internAtom :: Connection -> InternAtom -> IO (Receipt InternAtomReply) becomes: > internAtom :: Connection -> InternAtom -> IO (Receipt ATOM) Further work to make the API more "Haskelly" is ongoing. Related projects: X C Bindings: http://xcb.freedesktop.org/ -Antoine

2 2

how to link statically with a c lib ?
by minh thu 08 Feb '09

08 Feb '09

Hi, I'm writing bindings for the Tiny C Compiler. It seems that tcc provide a libtcc.a but no libtcc.so. In my cabal file, I have extra-libraries: dl, tcc but when using the generated haskell module, I have the following message : ⟨thu@jones samples⟩ ghc -e "main" Test.hs <interactive>: <command line>: can't load .so/.DLL for: tcc (libtcc.so: cannot open shared object file: No such file or directory) How can I generate a module linked statically against libtcc ? Thanks, Thu

2 4

any implementation of ACIO?
by Jianzhou Zhao 08 Feb '09

08 Feb '09

Hi, http://www.haskell.org/pipermail/haskell-cafe/2004-November/007715.html mentioned an interesting (A)ffine and (C)entral IO. Are there any packages or extensions to support ACIO in Haskell? Thanks JZ

2 1

[ANN] Working with HLint from Emacs
by Alex Ott 08 Feb '09

08 Feb '09

Hello For Emacs users it could be interesting - I wrote small module for more comfortable work with HLint from Emacs. It has same functionality as compilation-mode - navigation between errors, etc. To use it, just add following code to emacs init file: (require 'hs-lint) (defun my-haskell-mode-hook () (local-set-key "\C-cl" 'hs-lint)) (add-hook 'haskell-mode-hook 'my-haskell-mode-hook) Module is available from http://xtalk.msk.su/~ott/common/emacs/hs-lint.el -- With best wishes, Alex Ott, MBA http://alexott.blogspot.com/ http://xtalk.msk.su/~ott/ http://alexott-ru.blogspot.com/

6 7

Re: [Haskell-cafe] Just how unsafe is unsafe
by Yitzchak Gale 08 Feb '09

08 Feb '09

Peter Verswyvelen wrote: >>> I do have asked myself the question whether >>> a "really random generating" >>> function could be regarded as "pure" somehow I wrote: >> Not really... Alberto G. Corona wrote: > What is pure randomness? .When the algorithmic complexity of the list of > random number is equal to the lenght of the list, that is, is incompressible > by any means. But this can not be probed. the distribution of values gives a > hint of whether if the list obey any algorithm, but even so, many > compressible series have a random distribution. in practical terms, it is > random has a random distribution, the receiver does not know the algorithm > AND the initial value. In this case it can be pure. Perhaps philosophically you can consider it pure, but it is unsafe to treat it as pure in your program. If you write x = genRandomR (1, 100) then the compiler may or may not replace the variable x by the function application genRandomR (1, 100) anywhere in your program. That is probably not what you want. -Yitz

1 0

Moggi :: CT -> Hask
by Gregg Reynolds 08 Feb '09

08 Feb '09

Hi, I had a monadic revelation at about 3 am. The answer to the question "what is an IO value, really?" is "who cares?" I just posted a blog entry discussing how CT found it's way from Moggi into Haskell at http://syntax.wikidot.com/blog (hence the title; Moggi as functor). It addresses the question of what such things are and why Moggi's insight is so brilliant. Feedback welcome, but please remember this is coming from a non-mathematician who likes to write. If you find anything there that outrages your inner Russell, please correct me, but be gentle. Thanks, gregg

2 3

Just how unsafe is unsafe
by Andrew Wagner 08 Feb '09

08 Feb '09

So we all know the age-old rule of thumb, that unsafeXXX is simply evil and anybody that uses it should be shot (except when it's ok). I understand that unsafeXXX allows impurity, which defiles our ability to reason logically about haskell programs like we would like to. My question is, to what extent is this true? Suppose we had a module, UnsafeRandoms, which had a function that would allow you to generate a different random number every time you call it. The semantics are relatively well-defined, impurity is safely sectioned off in its own impure module, which is clearly labeled as such. How much damage does this do? Can we push the lines elsewhere? Is sectioning unsafeXXX into Unsafe modules a useful idiom that we can use for other things as well?

12 14

ANN: HLint 1.2
by Neil Mitchell 08 Feb '09

08 Feb '09

Hi, I am pleased to announce HLint version 1.2. HLint is a lint-like tool for Haskell that detects and suggests improvements for your code. HLint is compatible with most GHC extensions, and supports a wide variety of suggestions, and can be extended with additional user suggestions. To install: cabal update && cabal install hlint Web page: http://www-users.cs.york.ac.uk/~ndm/hlint/ Biggest new feature: List recursion suggestions. For example, running HLint over the GHC compiler now suggests things such as: Example.hs:3:1: Warning: Use foldr Found: seqList [] b = b seqList (x : xs) b = x `seq` seqList xs b Why not: seqList xs b = foldr seq b xs Example.hs:6:1: Warning: Use foldr Found: seqIds [] = () seqIds (id : ids) = seqId id `seq` seqIds ids Why not: seqIds ids = foldr (seq . seqId) () ids Example.hs:13:1: Warning: Use foldl Found: rev_app [] xs = xs rev_app (y : ys) xs = rev_app ys (y : xs) Why not: rev_app ys xs = foldl (flip (:)) xs ys HLint will automatically detect if you should have used a map, a foldr or a foldl and suggest how to change your code. In the GHC, darcs and Hoogle code bases there are no obvious map-like functions, which is a good sign :-) Changes from last time: * More GHC extensions supported - including record wild cards and fixes to a number of existing extensions. These changes are thanks to Niklas and the haskell-src-exts package. * Many infix operators are now correctly associated with the right priority. * All hints are now ignored, warnings or errors. Hopefully this should make it clearer what hints are most important. As part of this, the format for defining ignore files has changed completely - see the manual for the new format. * Lots of new hints have been added - many from users of HLint. * Many bugs have been fixed. Can any follow-up discussions please be directed to haskell-cafe@. All comments, questions, bug reports are welcome! Neil

13 33

Function const (Binding)
by TKM 07 Feb '09

07 Feb '09

Hello, I've a small question about the function const. I'm a bit of confused about how it binds. Let me take the following expression as example: const id 1 2 If I execute this expression, I will get as answer 2 with Helium. Now is my question, why doesn't it give me 1 as the answer? Because the type of id would be: a -> a. So first it would execute id 1 in my opinion. That gives us 1. And after executing const 1 2 it should give us 1. Can somebody explain to me why it does not bind as I expect? (I know I can do: const (id 1) 2 to get what I want) Thank you for your answers. Greetz TKM

3 2