Re: [Haskell-cafe] ghc panic when compiling blaze-builder

[kyra]

On 11/21/2010 3:20 AM, JosИ Romildo Malaquias wrote:

When compiling blaze-builder-0.2.0.1 with ghc-7.0.1 on my ~amd64 gentoo
system, I am getting the shown below.

Any clues?

Romildo


[...]
Building blaze-builder-0.2.0.1...
[1 of 8] Compiling Blaze.ByteString.Builder.Internal ( 
Blaze/ByteString/Builder/Internal.hs, 
dist/build/Blaze/ByteString/Builder/Internal.o )
ghc: panic! (the 'impossible' happened)
   (GHC version 7.0.1 for x86_64-unknown-linux):
dsLet: unlifted


Look here: http://hackage.haskell.org/trac/ghc/ticket/4498
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[Haskell-cafe] Same compiled program behaving differently when called from ghci and shell

[Bruno Damour]

Hello,
I have a very strange (for me) problem that I manage to reduce to this :
I have a small program that reads a file with 1 only character (è = e8)
The program is ftest2.hs :

import IO

import Data.Maybe

tfind s = lookup (head s) $ zip ['\xe8', '\xde'] "12"

main= do

h<- readFile "g:\\CODE\\rlib\\test.txt"

putStrLn h

print $ tfind h

I compile it from command line :

ghc --make ftest2.hs

Now the weird results :
1/ cmd line:

ftest2.exe

è

Just '2'

2/ ghci

Prelude>  :!ftest2.exe

è

Just '2'


3/WinGHci

Prelude>  :! ftest2.exe

è

Just '1'


I tested different variants, there is always a difference.
Any idea to help me trace this behaviour ?
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Re: [Haskell-cafe] Interactive OpenGL-based graphics and ghci?

[Lyndon Maydwell]

I've always had issues with GLUT under ghci. If GHC 7 fixes this it
will make me happy :)

On Sun, Nov 21, 2010 at 7:54 AM, Luke Palmer  wrote:
> On Sat, Nov 20, 2010 at 4:46 PM, Conal Elliott  wrote:
>> I'm trying to find some way to do interactive, OpenGL-based graphics in
>> Haskell on Mac OS X.
>> Does anyone here use GLUT or SDL on Mac OS X with ghci, or maybe an
>> alternative library?
>
> I was reading the GHC 7 release notes and saw this:
>
> * There is a new -fno-ghci-sandbox flag, which stops GHCi running
> computations in a separate thread; in particular, this works around an
> issue running GLUT from GHCi on OS X
>
> So that seems to indicate that GLUT would fulfill your needs.
>
> Luke
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Re: [Haskell-cafe] Downloading web page in Haskell

[Albert Y. C. Lai]

Most likely you also have the zlib package (cabal-install needs it), so 
let's use it. Attached therefore.hs


import qualified Data.ByteString.Lazy as LB
import Codec.Compression.GZip(decompress)
import Network.URI(parseURI)
import Network.HTTP

url = "http://www.adorocinema.com/common/search/search_by_film/?criteria=Bourne";

-- steal from getRequest but change type
-- it's lazy bytestring because the GZip library specifies it
myGetRequest :: String -> Request LB.ByteString
myGetRequest s = case parseURI s of
  Nothing -> error "url syntax error"
  Just uri -> mkRequest GET uri

main = do
  result <- simpleHTTP (insertHeader HdrAcceptEncoding "gzip" (myGetRequest url))
  case result of
Left e -> print e
Right rsp -> do
  let src = case findHeader HdrContentEncoding rsp of
Nothing -> rspBody rsp
Just "gzip" -> decompress (rspBody rsp)
Just _ -> error "TODO: other decompressions"
  LB.writeFile "test.html" src
  LB.putStrLn src
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Re: [Haskell-cafe] Downloading web page in Haskell

[Yitzchak Gale]

Albert Y. C. Lai wrote:
> ...truncates when the web server chooses the identity encoding
> The server chooses identity when
> your request's Accept-Encoding field specifies identity or simply your
> request has no Accept-Encoding field

Excellent work!

> My methodology of discovering and confirming this is a great lesson in the
> triumph of the scientific methodology (over the prevailing opinionative
> methodology, for example).

Haha, indeed!

> Actually the
> truncation strongly suggests that javascript is not involved: the truncation
> ends with an incomplete end-tag " javascript-heavy web pages.

Well, no, the theory was that the server sends some random
number of bytes from the body to ensure that the browser
starts loading the scripts in the head. So it could stop anywhere.

In the end, I think you didn't really need the W3C validator.
You also could have triangulated on the headers sent by your
own browser.

So, there you have it, folks. The Haskell community debugs
a broken web server, without being asked, and without access
to the server.
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Re: [Haskell-cafe] doesDirectoryExist is always returning False

[Judah Jacobson]

On Sat, Nov 20, 2010 at 6:55 AM, Marcelo Sousa  wrote:
> Hi,
> I'm having currently a problem with System.Directory in my mac os.
>   System Version: Mac OS X 10.6.5
>   Kernel Version: Darwin 10.5.0
> Prelude System.Directory> let dirTest = do {dir <- getCurrentDirectory;
> doesDirectoryExist dir}
> Prelude System.Directory> dirTest
> False

What's the output of getCurrentDirectory?  I just tried that on OS X
10.6.4 and dirTest returned True for me.

-Judah
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[Haskell-cafe] ghc panic when compiling blaze-builder

[José Romildo Malaquias]

When compiling blaze-builder-0.2.0.1 with ghc-7.0.1 on my ~amd64 gentoo
system, I am getting the shown below.

Any clues?

Romildo


[...]
Building blaze-builder-0.2.0.1...
[1 of 8] Compiling Blaze.ByteString.Builder.Internal ( 
Blaze/ByteString/Builder/Internal.hs, 
dist/build/Blaze/ByteString/Builder/Internal.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.0.1 for x86_64-unknown-linux):
dsLet: unlifted
AbsBinds
[b{tv aUH} [sk]]
[]
[pe{v axd} [lid] <= [b{tv aUH} [sk]] pe{v aUG} [lid]]
  pe{v axd} [lid]
:: forall b{tv aUH} [sk]. base:GHC.Ptr.Ptr{tc 33A} b{tv aUH} [sk]
  [LclId]
  { {273:19-54}
{273:19-54}
!((pe{v aUG} [lid] :: base:GHC.Ptr.Ptr{tc 33A} b{tv aUH} [sk]))
  = {273:30-54}
{273:33-41}
(base:GHC.Ptr.plusPtr{v r4X} [gid]) @ base:GHC.Word.Word8{tc 32U}
@ b{tv aUH} [sk]
  pf{v axc} [lid] firstBufSize{v arR} [lid] }
EvBinds{{}}
base:GHC.Base.>>={v 01P} [gid[ClassOp]]
  @ ghc-prim:GHC.Types.IO{tc 32I}
  $dMonad{v aUI} [lid]
  @ blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildSignal{tc 
rre}
  @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}
  (step0{v arY} [lid]
 pf{v axc} [lid] (pe{v axd} [lid] @ base:GHC.Word.Word8{tc 32U}))
  (\ (next{v axT} [lid]
:: 
blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildSignal{tc rre}) ->
 let {
   ds_d15b{v} [lid]
 :: 
blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildSignal{tc rre}
   [LclId]
   ds_d15b{v} [lid] = next{v axT} [lid] } in
 case ds_d15b{v} [lid] {ghc-prim:GHC.Types.IO{tc 32I}
  
bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}}
 of (wild_B1{v} [lid]
   :: 
blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildSignal{tc rre}) {
   blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.Done{d rrk} 
(rb_d15l{v} [lid]

  :: ghc-prim:GHC.Prim.Addr#{(w) tc 33}) ->
 let {
   pf'{v axU} [lid]
 :: base:GHC.Ptr.Ptr{tc 33A} base:GHC.Word.Word8{tc 32U}
   [LclId]
   pf'{v axU} [lid] =
 base:GHC.Ptr.Ptr{v rcP} [gid[DataCon]]
   @ base:GHC.Word.Word8{tc 32U} rb_d15l{v} [lid] } in
 let {
   fail_d15c{v} [lid]
 :: ghc-prim:GHC.Prim.State#{(w) tc 32q}
  ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}
-> ghc-prim:GHC.Types.IO{tc 32I}
 
bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}
   [LclId]
   fail_d15c{v} [lid] =
 \ (ds_d15d{v} [lid]
  :: ghc-prim:GHC.Prim.State#{(w) tc 32q}
   ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}) ->
   base:GHC.Base.${v 019} [gid]
 @ 
bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}
 @ (ghc-prim:GHC.Types.IO{tc 32I}
  
bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5})
 (base:GHC.Base.return{v 01T} [gid[ClassOp]]
@ ghc-prim:GHC.Types.IO{tc 32I}
$dMonad{v aUN} [lid]
@ 
bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5})
 
(bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.$WChunk{v reF} 
[gid[DataConWrapper]]
(mkbs{v axe} [lid] @ base:GHC.Word.Word8{tc 32U} pf'{v 
axU} [lid])
k{v arT} [lid]) } in
 case base:GHC.Classes.=={v 01L} [gid[ClassOp]]
@ (base:GHC.Ptr.Ptr{tc 33A} base:GHC.Word.Word8{tc 32U})
$dEq{v aUK} [lid]
pf'{v axU} [lid]
pf{v axc} [lid] {ghc-prim:GHC.Types.IO{tc 32I}
   
bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}}
 of (wild_B1{v} [lid] :: ghc-prim:GHC.Bool.Bool{(w) tc 3c}) {
   ghc-prim:GHC.Bool.False{(w) d 68} ->
 fail_d15c{v} [lid] ghc-prim:GHC.Prim.realWorld#{(w) v 0o} 
[gid];
   ghc-prim:GHC.Bool.True{(w) d 6u} ->
 base:GHC.Base.return{v 01T} [gid[ClassOp]]
   @ ghc-prim:GHC.Types.IO{tc 32I}
   $dMonad{v aUL} [lid]
   @ 
bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}
   k{v arT} [lid]
 };
   blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BufferFull{d 
rri} (rb_d15n{v} [lid]

:: ghc-prim:GH

Re: [Haskell-cafe] Downloading web page in Haskell

[Albert Y. C. Lai]

On 10-11-20 02:54 PM, José Romildo Malaquias wrote:

In order to download a given web page, I wrote the attached program. The
problem is that the page is not being full downloaded. It is being
somehow intettupted.


The specific website and url
http://www.adorocinema.com/common/search/search_by_film/?criteria=Bourne

truncates when the web server chooses the identity encoding (i.e., as 
opposed to compressed ones such as gzip). The server chooses identity 
when your request's Accept-Encoding field specifies identity or simply 
your request has no Accept-Encoding field, such as when you use 
simpleHTTP (getRequest url), curl, wget, elinks.


When the server chooses gzip (its favourite), which is when your 
Accept-Encoding field includes gzip, the received data is complete (but 
then you have to gunzip it yourself). This happens with mainstream 
browsers and W3C's validator at validator.w3.org (which destroys the 
"you need javascript" hypothesis). I haven't tested other compressed 
encodings.


Methodology

My methodology of discovering and confirming this is a great lesson in 
the triumph of the scientific methodology (over the prevailing 
opinionative methodology, for example).


The first step is to confirm or deny a Network.HTTP problem. For a 
maximally controlled experiment, I enter HTTP by hand using nc:


$ nc www.adorocinema.com 80
GET /common/search/search_by_film/?criteria=Bourne HTTP/1.1
Host: www.adorocinema.com


It still truncates, so at least Network.HTTP is not alone. I also try 
elinks. Other people try curl and wget for the same reason and the same 
result.


The second step is to confirm or deny javascript magic. Actually the 
truncation strongly suggests that javascript is not involved: the 
truncation ends with an incomplete end-tag "for very buggy javascript-heavy web pages. To certainly deny javascript 
magic, I first try Firefox with javascript off (also java off, flash 
off, even css off), and then I also ask validator.w3.org to validate the 
page. Both receive complete data. Of course the validator is going to 
say "many errors", but the point is that if the validator reports errors 
at locations way beyond our truncation point, then the validator sees 
data we don't see, and the validator doesn't even care about javascript.


The validator may be very sophisticated in parsing html, but in sending 
an HTTP request it ought to be very simple-minded. The third step is to 
find out what extra thing the validator does to deserve complete data. 
So I try diagonalization: I give this CGI script to the validator:


#! /bin/sh

echo 'Content-Type: text/html'
echo ''
e=`env`
cat