Re: [Haskell-cafe] Importing more modules by default

[aditya bhargava]

Cool, BasicPrelude solves my problem perfectly!



On Thu, Aug 8, 2013 at 7:04 AM, David McBride  wrote:

> I've started using BasicPrelude with -XNoImplicitPrelude in all of my
> code.  It imports all of those and some other stuff as well (text related
> functions).  Cuts down on my imports by a little over half.  Kind of wish
> it could be made the default.
>
>
> On Wed, Aug 7, 2013 at 10:23 PM, aditya bhargava  > wrote:
>
>> Hi there,
>> It seems like every Haskell program I write imports the following modules:
>>
>> Control.Monad
>> Control.Applicative
>> Data.Maybe
>> Data.List
>>
>> Is there a good reason why these modules aren't imported by default? When
>> I write a simple script usually a 1/4th of the script is just imports, and
>> my code just looks uglier.
>>
>> Adit
>>
>> ___
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>>
>>
>


-- 
adit.io
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Re: [Haskell-cafe] Installling Leksah on ghc7.6.3 with haskell-platform 2013?

[Carlo Hamalainen]

On 09/08/13 16:35, Hamish Mackenzie wrote:

You will need Leksah 0.13 for GHC 7.6.3 and it is not in Hackage yet.

It is almost ready though.  If run

git clone https://github.com/leksah/leksah.git
cd leksah
cabal install cabal-meta cabal-src
cabal-meta install

It would be interesting to know if it works for you.


On an up to date Debian Wheezy system with ghc 7.6.3, haskell platform 
2013, git 1.7.10.4:


✓ 11:51:58 carlo@x1 (master) ~/tmp/leksah $ cabal-meta install
git fetch origin
git checkout master
Already on 'master'
git submodule foreach git pull origin master
You need to run this command from the toplevel of the working tree.
cabal-meta:
log of commands saved to: /home/carlo/tmp/leksah/.shelly/1.txt
Exception: error running: git submodule foreach git pull origin master
exit status: 1
stderr: You need to run this command from the toplevel of the working tree.

So instead I tried the initial git clone with --recursive, but there are 
some fatal errors (references that are not in the tree?).


✓ 12:01:44 carlo@x1 ~/tmp $ git clone --recursive 
https://github.com/leksah/leksah.git

Cloning into 'leksah'...
WARNING: gnome-keyring:: couldn't connect to: 
/home/carlo/.cache/keyring-yZXClI/pkcs11: No such file or directory

remote: Counting objects: 8930, done.
remote: Compressing objects: 100% (2431/2431), done.
remote: Total 8930 (delta 6145), reused 8824 (delta 6044)
Receiving objects: 100% (8930/8930), 17.53 MiB | 538 KiB/s, done.
Resolving deltas: 100% (6145/6145), done.
Submodule 'vendor/CodeMirror' (g...@github.com:ghcjs/CodeMirror.git) 
registered for path 'vendor/CodeMirror'
Submodule 'vendor/ghcjs-dom' (g...@github.com:ghcjs/ghcjs-dom.git) 
registered for path 'vendor/ghcjs-dom'
Submodule 'vendor/haskellVCSGUI' 
(g...@github.com:leksah/haskellVCSGUI.git) registered for path 
'vendor/haskellVCSGUI'
Submodule 'vendor/haskellVCSWrapper' 
(g...@github.com:leksah/haskellVCSWrapper.git) registered for path 
'vendor/haskellVCSWrapper'
Submodule 'vendor/jsc' (g...@github.com:ghcjs/jsc.git) registered for 
path 'vendor/jsc'
Submodule 'vendor/leksah-server' 
(g...@github.com:leksah/leksah-server.git) registered for path 
'vendor/leksah-server'
Submodule 'vendor/ltk' (g...@github.com:leksah/ltk.git) registered for 
path 'vendor/ltk'
Submodule 'vendor/pretty-show' (g...@github.com:leksah/pretty-show.git) 
registered for path 'vendor/pretty-show'
Submodule 'vendor/vado' (g...@github.com:hamishmack/vado.git) registered 
for path 'vendor/vado'
Submodule 'vendor/webkit-javascriptcore' 
(g...@github.com:ghcjs/webkit-javascriptcore.git) registered for path 
'vendor/webkit-javascriptcore'
Submodule 'vendor/yi' (g...@github.com:leksah/yi.git) registered for path 
'vendor/yi'

Cloning into 'vendor/CodeMirror'...
X11 forwarding request failed on channel 0
remote: Counting objects: 14210, done.
remote: Compressing objects: 100% (6388/6388), done.
remote: Total 14210 (delta 8658), reused 13125 (delta 7792)
Receiving objects: 100% (14210/14210), 2.95 MiB | 543 KiB/s, done.
Resolving deltas: 100% (8658/8658), done.
Submodule path 'vendor/CodeMirror': checked out 
'107612c9e854c61ed3aa94bee29a136438085557'

Cloning into 'vendor/ghcjs-dom'...
X11 forwarding request failed on channel 0
remote: Counting objects: 813, done.
remote: Compressing objects: 100% (483/483), done.
remote: Total 813 (delta 578), reused 546 (delta 313)
Receiving objects: 100% (813/813), 363.52 KiB | 173 KiB/s, done.
Resolving deltas: 100% (578/578), done.
Submodule path 'vendor/ghcjs-dom': checked out 
'c347df82e86136851b9d132d1c71d18ecb3f9f2a'

Cloning into 'vendor/haskellVCSGUI'...
X11 forwarding request failed on channel 0
remote: Counting objects: 1239, done.
remote: Compressing objects: 100% (533/533), done.
remote: Total 1239 (delta 688), reused 1227 (delta 677)
Receiving objects: 100% (1239/1239), 13.05 MiB | 537 KiB/s, done.
Resolving deltas: 100% (688/688), done.
Submodule path 'vendor/haskellVCSGUI': checked out 
'5aaf804587c9e8b34dd669390666cdbcba564e4c'

Cloning into 'vendor/haskellVCSWrapper'...
X11 forwarding request failed on channel 0
remote: Counting objects: 1019, done.
remote: Compressing objects: 100% (432/432), done.
remote: Total 1019 (delta 569), reused 1008 (delta 558)
Receiving objects: 100% (1019/1019), 2.66 MiB | 525 KiB/s, done.
Resolving deltas: 100% (569/569), done.
Submodule path 'vendor/haskellVCSWrapper': checked out 
'00e0ed2f007a8ca68d1b8a4ebf66a86b572b9647'

Cloning into 'vendor/jsc'...
X11 forwarding request failed on channel 0
remote: Counting objects: 221, done.
remote: Compressing objects: 100% (146/146), done.
remote: Total 221 (delta 95), reused 149 (delta 27)
Receiving objects: 100% (221/221), 48.26 KiB, done.
Resolving deltas: 100% (95/95), done.
Submodule path 'vendor/jsc': checked out 
'99047d74b7036a4bf9172af548b9c80498f7a3c9'

Cloning into 'vendor/leksah-server'...
X11 forwarding request failed on channel 0
remote: Counting objects: 950, done.
remote: Compressing objects: 100% (437/437), done.
remote:

Re: [Haskell-cafe] Some philosophy (Was: Alternative name for return)

[Kim-Ee Yeoh]

On Fri, Aug 9, 2013 at 10:44 PM, Jerzy Karczmarczuk <
jerzy.karczmarc...@unicaen.fr> wrote:

> I decided to reread some philosophical texts, and I suggest one for your
> evening reading.
>
> "Indiscrete Thoughts" by Gian-Carlo Rota, published by Birkhäuser in 1997.
> Available on the Web.
>

I'm rather fond of Rota's two volumes of musings. For the purpose of
furthering the quality of philosophizing, would it not be better served
citing the relevant chapters, if not the actual page numbers?

As you took note, the book covers a swathe of topics.

-- Kim-Ee
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Re: [Haskell-cafe] Some philosophy (Was: Alternative name for return)

[man]

On Fri, Aug 9, 2013 at 5:44 PM, Jerzy Karczmarczuk <
jerzy.karczmarc...@unicaen.fr> wrote:

> I have the impression that a nice part of our dispute comes from the fact
> that despite our ambitions, and a decent /technical/ level of understanding
> of what we are talking about, most of us are (and I am one of the worst...)
> --
>
> -- pitiful philosophers...
>


I just leave this here,

Analytic Philosophy: An Anthology

http://www.amazon.com/gp/product/0631216472

-- 
happy hacking... man
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[Haskell-cafe] Some philosophy (Was: Alternative name for return)

[Jerzy Karczmarczuk]

I have the impression that a nice part of our dispute comes from the 
fact that despite our ambitions, and a decent /technical/ level of 
understanding of what we are talking about, most of us are (and I am one 
of the worst...) --


-- pitiful philosophers...

Really bad...
Confusing the contents and the function/role of the entities,
using ambiguous definitions (and confounding objects with their 
definitions),

et j'en passe.

Sigh.

I decided to reread some philosophical texts, and I suggest one for your 
evening reading.


"Indiscrete Thoughts" by Gian-Carlo Rota, published by Birkhäuser in 
1997. Available on the Web.


Rota was an active *mathematician* and teacher, and the sense of 
mathematical constructs was very important for him. It is a very 
refreshing book, you won't be disappointed.
(It contains also some personal views of Rota on his fellows 
mathematicians. And the analysis of the difference between characters 
who are "problem solvers", as contrasted with "theoreticians"... Rota 
was a strong personality, full of "obsessions", and his ideas on the 
soundness of formal thinking may not convince you, but you should find 
them interesting. And you will find inside that for Rota the term 
"should" is very important, even if it impossible to define...)


Many thanks to Olivier Danvy, who recommended me this book!

Jerzy Karczmarczuk
Caen, France.


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Re: [Haskell-cafe] Diagrams and GTK

[Claude Heiland-Allen]

Hi Michael,

On 09/08/13 08:21, Michael Oswald wrote:
> Hello,
> 
> I am currently writing an application which draws the structure of some
> packets with help of the diagrams library directly to a GTK GUI.
> 
> Now the packets can have several hundreds of parameters which have to be
> drawn so it takes some seconds to calculate the diagram itself. Of
> course this now blocks the GUI thread, so the basic idea was to put the
> calculation in a separate thread. Unfortunately this doesn't work as
> lazyness kicks in and the final diagram is calculated when it is
> rendered and not evaluated before. Using seq didn't help (because of
> WHNF) and there seems to be no deepseq instance for the diagrams.
> 
> Does somebody has an idea on how to speed this up / get the diagram
> evaluated strictly as especially scrolling the DrawingArea is now really
> a pain?

Cairo is thread safe* so you could render the whole thing (if it isn't
super huge dimensions) to an image surface in the background thread,
then displaying could be a matter of copying the correct part (for
scrolling) of the surface to the DrawingArea.

Something like this perhaps (untested, incomplete):

8<
import qualified Diagrams.(...) as D
import qualified Graphics.Rendering.Cairo as C

renderDiaToSurface width height diagram = do
  let w' = fromIntegral width
  h' = fromIntegral height
  opts = D.CairoOptions "" (D.Dims w' h') D.RenderOnly False
  (_, render) = D.renderDia D.Cairo opts diagram
  surface <- C.createImageSurface C.FormatARGB32 width height
  C.renderWith surface render
  return surface

...
8<


Hope this is useful,


Claude

* I had some very rare crashes in heavily threaded code, still not found
the root cause...

-- 
http://mathr.co.uk


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Re: [Haskell-cafe] translate imperative pseudo code into haskell

[Frerich Raabe]

On 2013-08-09 17:28, Frerich Raabe wrote:

On 2013-08-09 17:04, Joerg Fritsch wrote:

for 0 <= i < row dimension of A
 for 0 <= j < column dimension of B
   for 0 <= k < column dimension of A = row dimension of B
 sum += (read A (i,k))* (read B(k,j))


[..]


-- This is one way to write your pseudo code in Haskell
products :: Matrix -> Matrix -> Int
products a b = sum $ do
  i <- [1..rows a]
  j <- [1..columns b]
  k <- [1..columns a]
  return $ readValue a (i, k) * readValue b (k, j)


It just occurred to me that the ranges of i, j and k are not quite
correct, e.g. [1..rows a] should be [0..rows a - 1] to match your
pseudo code. That aside, 'products' is probably not a very
appropriate name.

In any case, you could also keep your approach of building all
3-tuples and then map a function which turns the tuples into
products over the list, like:

  products :: [(Int, Int, Int)] -> [Int]
  products = map (\i j k -> readA (i, j) * readB (k, j))

...and then call 'sum' on that. This function actually deserves
the name. :-)

--
Frerich Raabe - ra...@froglogic.com
www.froglogic.com - Multi-Platform GUI Testing

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Re: [Haskell-cafe] translate imperative pseudo code into haskell

[Frerich Raabe]

On 2013-08-09 17:04, Joerg Fritsch wrote:

I would need some help to get to a reasonable function involving the
DB read, addition and multiplication.

for 0 <= i < row dimension of A

 for 0 <= j < column dimension of B

   for 0 <= k < column dimension of A = row dimension of B

 sum += (read A (i,k))* (read B(k,j))

I started like this but then somehow lost the compass:

main = do

 map my.read (map ((x,y) -> "matrixA:" ++ show row ++ ":" ++ show 
column) [ (i, j, k) | i <- [1..50], j <- [1..20], k <- [1..30] ])


You could treat lists as monads and write code which looks very much 
like your pseudo code, something like this


-- A few dummy definitions to make 'products' typecheck.
data Matrix = Matrix

rows :: Matrix -> Int
rows = undefined

columns :: Matrix -> Int
columns = undefined

readValue :: Matrix -> (Int, Int) -> Int
readValue = undefined

-- This is one way to write your pseudo code in Haskell
products :: Matrix -> Matrix -> Int
products a b = sum $ do
  i <- [1..rows a]
  j <- [1..columns b]
  k <- [1..columns a]
  return $ readValue a (i, k) * readValue b (k, j)

--
Frerich Raabe - ra...@froglogic.com
www.froglogic.com - Multi-Platform GUI Testing

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[Haskell-cafe] ANN: hi-0.0.2, a Haskell project generator

[Daisuke Fujimura]

Hello cafe,

I'm very happy to announce the release of hi, a Haskell project generator.

http://hackage.haskell.org/package/hi

This application will generate a scaffold for new Haskell project with
given command line argument(or value in configuration file), using git
repository as a template.

If you frequently create new project which has test suite in hspec,
generating new project by hi will be a good alternative to cabal-init. It
comes with test suite in hspec and already buildable.

A project made by the default configuration is here.
https://github.com/fujimura/hi-example

More details is in the README:
https://github.com/fujimura/hi

Hope you enjoy it :-)

--
Fujimura Daisuke
http://fujimuradaisuke.com/
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[Haskell-cafe] translate imperative pseudo code into haskell

[Joerg Fritsch]

I would need some help to get to a reasonable function involving the DB
read, addition and multiplication.

 

for 0 <= i < row dimension of A

 for 0 <= j < column dimension of B

for 0 <= k < column dimension of A = row dimension of B

   sum += (read A (i,k))* (read B(k,j))

 

 

I started like this but then somehow lost the compass:

 

main = do

   map my.read (map (\(x,y) -> "matrixA:" ++ show row ++ ":" ++ show
column) [ (i, j, k) | i <- [1..50], j <- [1..20], k <- [1..30] ]) 

 

Can you pls help?

 

--Joerg

 

 

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Re: [Haskell-cafe] Alternative name for return

[Kim-Ee Yeoh]

On Thu, Aug 8, 2013 at 7:40 AM, Timon Gehr  wrote:

>  You make the distinction between "evaluate",
>>
>
> Which essentially means applying reduction rules to an expression until
> the result is a value.
>
>  and  "execute" or "run", etc. This is not functional.
>>
>
> How would you know?
>

I think Jerzy is alluding to the fact that we don't have a denotational
semantics for IO. So I'm not sure I understand your response. Are you
pointing out that some subspace of IO programs admit such a semantics via
an easy inspection?

'putStr "c"' is a pure value.


This is the crux of the matter: "pure value" means different things to
different people.

Some employ it to mean an effectful monadic expression to distinguish
between getLine and (return "Hello"), both of type IO String.

Others use it to distinguish between an ordinary Haskell expression and,
say, C.

So when you write:

> 'unsafePerformIO (putStr "c")' is not a pure value.

I infer you're in the latter camp.

Would you then speak of 'effectful' values vs 'null-effectful' ones? What
oral syntax would you actually use?

-- Kim-Ee


On Thu, Aug 8, 2013 at 7:40 AM, Timon Gehr  wrote:

> On 08/08/2013 01:19 AM, Jerzy Karczmarczuk wrote:
>
>> Bardur Arantsson comments the comment of Joe Quinn:
>>
>>> >On 8/7/2013 11:00 AM, David Thomas wrote:

> >>twice :: IO () -> IO ()
> >>twice x = x >> x
> >>
> >>I would call that evaluating x twice (incidentally creating two
> >>separate evaluations of one pure action description), but I'd like to
> >>better see your perspective here.
>
 >
 >x is only evaluated once, but/executed/  twice. For IO, that means

 >magic. For other types, it means different things. For Identity, twice
 =
 >id!
 >

>>> Your point being? x is the same thing regardless of how many times you
>>> run it.
>>>
>>
>> What do you mean by "the same thing"? You cannot compare 'them' in any
>> reasonable sense.
>> ...
>>
>
> http://en.wikipedia.org/wiki/**Identity_of_indiscernibles
>
> (He is reasoning _about_ the language and not _within_ the language
> because Haskell does not support very powerful reasoning internally.)
>
>  ...
>>
>> You make the distinction between "evaluate",
>>
>
> Which essentially means applying reduction rules to an expression until
> the result is a value.
>
>
>  and  "execute" or "run", etc. This is not functional.
>>
>
> How would you know?
>
>  Your program doesn't "run" anything, it
>> applies (>>=) (or equivalent) to an IO (...) object. This is the only
>> "practical evaluation" of it, otherwise it can  be passed (or duplicated
>> as above). But you cannot apply "bind" twice to the same instance of it
>> (in fact, as I said above, "the same instance"  is a bit suspicious
>> concept...).
>> ...
>>
>
> Indeed, but you didn't say that above.
>
>
>  The "running" or "execution" takes place outside of your program. In
>> such a way Richard O'Keefe and I converge... That's why I say that the
>> concept of purity is meaningless in the discussed context.
>>
>
> Not meaningless, but redundant. The point of having a purely functional
> programming language is to have reasoning based on purity be universally
> applicable.
>
>  It is a kind of counterfeit notion, inherited from "pure functions" to
>> something
>> which belongs to two different worlds.
>> ...
>>
>
> 'putStr "c"' is a pure value.
>
> On the other hand:
>
> 'unsafePerformIO (putStr "c")' is not a pure value.
>
> (But this expression does not exist in standard Haskell. unsafePerformIO
> "unquotes" the action. You may be confusing the "quoted" and "unquoted"
> versions.)
>
>
>
> __**_
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/**mailman/listinfo/haskell-cafe
>
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Re: [Haskell-cafe] Why are field selectors functions?

[David Banas]

Wouldn't the implementation hiding feature of the *newtype *idiom be
broken, if field selectors were not first class functions? For instance,
the following code (taken shamelessly from Ch. 10 of *Real World Haskell*):

module Parse (
runParser
) where

data ParseState = ParseState {
string :: String
} deriving (Show)

newtype Parser a = Parser {
runParser :: ParseState -> Either String (a, ParseState)
}


has the attractive feature of hiding the internal implementation of
the *ParseState
*and *Parser *types from the user, preventing him from, for instance,
pattern matching on either and thus writing code, which may break when we
change the implementation. I believe this is only possible, because
the *runParser
*accessor is exportable as a first class function.
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Re: [Haskell-cafe] ANN: hi2 -- a better indentation mode for Emacs' haskell-mode

[Tom Ellis]

On Fri, Aug 09, 2013 at 12:53:56PM +0200, Gergely Risko wrote:
> In the last 2-3 weeks I've been working on Haskell indentation inside
> Emacs.  I had some annoyances for a long time and fixed some of them.
> 
> The new mode is called hi2, it's heavily based on the current
> haskell-indentation (part of haskell-mode).  The changes are mainly to
> the UI, although, I plan to have a look on the parser too.
> 
> The code can be found on github: https://github.com/errge/hi2.  Feel
> free to send me feedback, bug reports, pull requests, etc.

Just tried it and I already like it!  Thanks.

Tom

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[Haskell-cafe] ANN: hi2 -- a better indentation mode for Emacs' haskell-mode

[Gergely Risko]

Hi,

In the last 2-3 weeks I've been working on Haskell indentation inside
Emacs.  I had some annoyances for a long time and fixed some of them.

The new mode is called hi2, it's heavily based on the current
haskell-indentation (part of haskell-mode).  The changes are mainly to
the UI, although, I plan to have a look on the parser too.

The code can be found on github: https://github.com/errge/hi2.  Feel
free to send me feedback, bug reports, pull requests, etc.

It's also hosted on MELPA.

The most notable changes so far are the following:

  - DEL and C-d is not mapped: if you want to indent backwards, you can
use S-TAB.  This means no random jumping on backspace anymore.

  - TAB steps to the right as before, but when the end is reached, it
starts going to the left instead of wrapping around.

  - TAB stays inside the code, instead of going to the beginning of the
line.  As in pyhton-mode and perl-mode.

  - Region indentation common case is supported: TAB and S-TAB is simply
moving the whole region to the left/right by 1-column.  Can be
pressed repeatedly.

  - The current indentations are shown as underscores in the current
line.  So you have some visual indication on what's gonna happen.
Also useful while hacking on the parser and want to see the results.
Can be turned off by setting hi2-show-indentations to nil in your
init file or calling hi2-disable-show-indentations from the buffer.
If there are collisions with other overlay hacking modes
(e.g. fill-column-indicator), try to turn off
hi2-show-indentations-after-eol.

  - The buffer is not changed when indentation is not changed (so there
are no undo points created and no dirty flag in the buffer if
pressing TAB had no effect).

  - The code for all this is somewhat commented and cleaned.

I'm not trying to fork haskell-mode, it's maintained very actively on
github and the maintainers were always friendly through code reviews.
But the current haskell-indentation-mode required so many fixes that it
became unpleasant to contribute patch-by-patch, I wanted to move fast.
When (and if) hi2 gets stable and better in every respect than
haskell-indentation-mode, I'm happy to merge and contribute it back.

Gergely


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Re: [Haskell-cafe] starting GHC development -- two questions

[Richard Eisenberg]

You may also want to check out this freshly-minted page on the wiki:
http://ghc.haskell.org/trac/ghc/wiki/Newcomers

Every now and again, someone asks exactly the same question that you 
did, so I've created that page to help answer it. I hope you find it 
useful.


Happy hacking!

Richard

On 2013-08-09 00:25, Ömer Sinan Ağacan wrote:

Hello Edward,


First off, welcome to the wonderful world of GHC development!  I
recommend that you subscribe to the ghc-devs mailing list and
direct GHC specific questions there:

http://www.haskell.org/mailman/listinfo/ghc-devs


Thanks, I didn't know that. I subscribed and I will ask further
questions to that list.

GHC has a 'make tags' command but I've never gotten it to work.  I 
have

always just run 'hasktags .' in the compiler/ directory, which works
pretty well for me.  (If you're in the RTS, run ctags, etc instead)


Great! It worked at the first try and I already started using it.


We've been discussing putting together an easy bugs list.  As a proxy,
you can search on the 'Difficulty' keyword:
http://ghc.haskell.org/trac/ghc/query?status=infoneeded&status=merge&status=new&status=patch&difficulty=Easy+(less+than+1+hour)&col=id&col=summary&col=status&col=type&col=priority&col=milestone&col=component&order=priority

For example, this bug seems like a good beginner bug to get your feet
wet with the RTS: http://ghc.haskell.org/trac/ghc/ticket/750

This one will give you some experience wrangling the test suite:
http://ghc.haskell.org/trac/ghc/ticket/8079

Moving up to the moderate category, here is a nontrivial bug involving
profiling and the optimizer: 
http://ghc.haskell.org/trac/ghc/ticket/609


As with all open source projects, there is always lots of
infrastructural work to be done, so if that's your sort of thing, 
there

are plenty of bugs in that category.


Thanks, I'll start looking for issues with easy difficulty for now and
ask further questions to ghc-devs mailing list.

---
Ömer Sinan Ağacan
http://osa1.net

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Re: [Haskell-cafe] Errors with Template Haskell

[Jose A. Lopes]

Thank you!

-- 
Jose Antonio Lopes
Ganeti Engineering
Google Germany GmbH
Dienerstr. 12, 80331, München

Registergericht und -nummer: Hamburg, HRB 86891
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Re: [Haskell-cafe] Errors with Template Haskell

[Edsko de Vries]

The Template Haskell quotation monad (Q) has proper support for fail:

module A where

import Language.Haskell.TH

foo :: Q Exp
foo = fail "Custom compile error!"

and

module B where

import A

main :: IO ()
main = print $foo

gives

B.hs:6:14:
Custom compile error!
In the first argument of `print', namely `$foo'
In the expression: print ($foo)
In an equation for `main': main = print ($foo)

-E

On Fri, Aug 9, 2013 at 9:48 AM, Jose A. Lopes  wrote:
> Hi,
>
> In Template Haskell, what is the proper way of signalling an error ?
>
> For example, you are generating code and you detect that a given
> parameter does not fulfill a precondition (e.g., String is empty), and
> you want to abort compilation with a descriptive error message.
>
> Thanks,
> Jose
>
> --
> Jose Antonio Lopes
> Ganeti Engineering
> Google Germany GmbH
> Dienerstr. 12, 80331, München
>
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg
> Geschäftsführer: Graham Law, Christine Elizabeth Flores
> Steuernummer: 48/725/00206
> Umsatzsteueridentifikationsnummer: DE813741370
>
> ___
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[Haskell-cafe] Errors with Template Haskell

[Jose A. Lopes]

Hi,

In Template Haskell, what is the proper way of signalling an error ?

For example, you are generating code and you detect that a given
parameter does not fulfill a precondition (e.g., String is empty), and
you want to abort compilation with a descriptive error message.

Thanks,
Jose

-- 
Jose Antonio Lopes
Ganeti Engineering
Google Germany GmbH
Dienerstr. 12, 80331, München

Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
Geschäftsführer: Graham Law, Christine Elizabeth Flores
Steuernummer: 48/725/00206
Umsatzsteueridentifikationsnummer: DE813741370

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Re: [Haskell-cafe] Haskell Platform and Leksah on Windows

[Alberto G. Corona]

For those who want to be productive rather than  talkative masoquists (thus
said with all my love ;)), there are windows installers for Leksah and they
work perfectly well.


2013/8/9 David Virebayre 

> Hi,
>
> If you go the EclipseFP approach, you may have installations troubles
> too. In my case, it was due to having a version of GHC and libraries
> that EclipseFP doesn't like.
>
> Once I got it to work,  I loved it.
>
> David.
>
>
> 2013/8/8 Dorin Lazar :
> > Hi,
> > I understood what's wrong about my approach - and since I want to use
> > an IDE to assist me, I will try both EclipseFP and Sublime Text, to
> > see how that works. My feeling was that since the leksah website
> > suggested that cabal is the way to do it and since when I search for a
> > Haskell IDE that is it, then it was obvious that the recommended way
> > doesn't work as it should. In my mind the platform was broken, I
> > understand now that it's not the platform, just this special way of
> > using it.
> >
> > I was also in awe of the fact that nobody really says anything about
> > these difficulties, and felt like an estranged child that messed
> > things up badly; however, it seems that the real issue is that nobody
> > really does it that way, and I was wrong to actually try it like that.
> > As I said (or haven't, but will) once I will get the hang of it I will
> > recount my experience for others to follow, hopefully in better terms
> > than this frustrating first experience.
> >
> > Many thanks for everyone's advice on the list,
> >   Dorin
> >
> > On Thu, Aug 8, 2013 at 9:48 PM, Carter Schonwald
> >  wrote:
> >> Hey Dorin,
> >> I don't understand your claims.
> >>
> >> 1) haskell has worked perfectly well on windows for quite some time. I
> used
> >> HUGs nearly a decade ago, and in more recent time (2-3 years ago) I
> helped
> >> teach an introductory first computer science class using GHC where many
> >> students were doing great work using notepad++ and ghci.
> >>
> >>  I don't understand your focus on emacs and make files.
> >>
> >> 2)  if you want an "IDE" experience, Sublime Text with the right
> plugins, or
> >> perhaps EclipseFP are worth checking out.
> >>
> >> 3) likewise, if you're finding tooling on windows unsatisfactory, help
> fix
> >> it! Bug reports, patches, or new tools and libraries are always welcome.
> >> Haskell is a relatively small community, and thusly limited manpower
> (we're
> >> all volunteers), so way to fix any problem is help out!
> >>
> >> cheers
> >>
> >>
> >> On Thu, Aug 8, 2013 at 3:30 AM, Dorin Lazar 
> wrote:
> >>>
> >>>  Hello,
> >>>  I am the original author of the post, and I finally received the
> >>> emails from the mailman (probably there was an issue with the
> >>> automated requests).
> >>>   My answers are inlined.
> >>>
> >>> > 1) Leksah should not be considered an "official haskell ide", but
> merely
> >>> > one of
> >>> > many community supported editing tools. And frankly one of the less
> >>> > widely
> >>> > used ones at that! Leksah is not used much at all by anyone, though
> >>> > theres
> >>> > probably a handful of folks who do use it.
> >>> >  Many folks use editors like Sublime Tex (2/3), Emacs, Vi(m),
> textmate,
> >>> > and
> >>> > many more.  Its worth noting that the sublime-haskell plugin for
> sublime
> >>> > text, and analogous packages for many other editors, provide haskell
> >>> > IDE-like powers, or at least a nice subset thereof.
> >>>   Unfortunately, I think the problem with this is that we have a
> >>> different vision on how development should be done. I have extensive
> >>> experience of working from console, with a simple text editor and
> >>> hand-made Makefiles or anything similar. However, an IDE should be a
> >>> productivity tool, that can help you improve your understanding of the
> >>> language, and can assist you in following the proper syntax for a new
> >>> language. While learning by doing 'write, save, compile, examine error
> >>> message' is ok with me, it is slow, and it limits the time I can
> >>> dedicate to learning the language itself. A better cycle is the
> >>> current 'write, examine error message' of most IDEs, since it's faster
> >>> and requires no context switch. Sure, editors can help there. IDEs do
> >>> this by default.
> >>>   So it's normal of me to search for an IDE to better learn the
> >>> language, I'll leave the emacs + console version for when I am
> >>> productive in the language.
> >>>
> >>> > 2) There are people working on building better easily portable native
> >>> > gui
> >>> > toolkits, but in many respects, a nice haskelly gui toolkit is still
> >>> > something people are experimetning with how to do well. theres lots
> of
> >>> > great
> >>> > tools out as of the past year or two, many more in progress on
> various
> >>> > time
> >>> > scales, and gtk2hs is great for linux (and thats fine).
> >>>   Unfortunately, this is not what's advertised. In fact, on the leksah
> >>> site, the recommended method is to

[Haskell-cafe] Diagrams and GTK

[Michael Oswald]

Hello,

I am currently writing an application which draws the structure of some 
packets with help of the diagrams library directly to a GTK GUI.


Now the packets can have several hundreds of parameters which have to be 
drawn so it takes some seconds to calculate the diagram itself. Of 
course this now blocks the GUI thread, so the basic idea was to put the 
calculation in a separate thread. Unfortunately this doesn't work as 
lazyness kicks in and the final diagram is calculated when it is 
rendered and not evaluated before. Using seq didn't help (because of 
WHNF) and there seems to be no deepseq instance for the diagrams.


Does somebody has an idea on how to speed this up / get the diagram 
evaluated strictly as especially scrolling the DrawingArea is now really 
a pain?


lg,
Michael


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