[Haskell-cafe] help

6 Dec 2009


      On Sun, Dec 6, 2009 at 4:53 AM,  wrote:
...
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Today's Topics:
1. Re: Low Level Audio - Writing bytes to the sound card?
     (Daniel Fischer)
  2. Re: HP + Gtk2hs? (M Xyz)
  3. Re: Low Level Audio - Writing bytes to the sound card? (M Xyz)
  4. Re: Low Level Audio - Writing bytes to the sound card?
     (Daniel Fischer)
  5. RE: Low Level Audio - Writing bytes to the sound card? (john lask)
  6. Re: New Hackage category: Error Handling (Henning Thielemann)
  7. Re: Low Level Audio - Writing bytes to the sound card? (M Xyz)
  8. RE: Low Level Audio - Writing bytes to the sound card? (M Xyz)
  9. PortAudio library successfully built on Windows (M Xyz)
 10. When are undecidables ok? (Michael Snoyman)
 11. Re: When are undecidables ok? (Luke Palmer)
 12. Re: When are undecidables ok? (Michael Snoyman)
 13. Re: ANNOUNCE:  error-message (Ariel J. Birnbaum)
 14. Re: What is the rank of a polymorphic type? (Eugene Kirpichov)
 15. Re: universal binary version of Haskell Platform?
     (Benjamin L.Russell)
 16. Re: What is the rank of a polymorphic type? (Dan Doel)
 17. Re[2]: [Haskell-cafe] Low Level Audio - Writing bytes to the
     sound     card? (Bulat Ziganshin)
 18. Re: universal binary version of Haskell Platform?
     (Heinrich Apfelmus)
 19. Re: Low Level Audio - Writing bytes to the sound card?
     (Andrew Coppin)
 20. Re: binding to C libraries on Windows was Low Level       Audio -
     Writing bytes to the sound card? (Andrew Coppin)
---------- Forwarded message ----------
From: Daniel Fischer 
To: haskell-cafe@haskell.org
Date: Sun, 6 Dec 2009 01:24:17 +0100
Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
Am Sonntag 06 Dezember 2009 00:47:38 schrieb M Xyz:
...
Daniel, Thank you for your thoughtful reply. I didn't know about those
flags. The log is fairly long, and as I'm new to Haskell and Cabal it is
mostly meaningless to me. I see very many incidences of "searching for

...
in path. Cannot find ___ on the path" so maybe this is all as simple as
me
not setting my environment correctly.
If you have cpphs, hugs, jhc, greencard etc., it is probably something
about your
environment. If you don't have them, it's clear that they aren't found.
On the other hand, that doesn't explain
Using c2hs version 0.16.0 given by user at: C:\Program
Files\Haskell\bin\c2hs.exe
-- so it finds c2hs, and can apparently run c2hs --version
("C:\\Program
Files\\Haskell\\bin\\c2hs.exe",["--include=dist\\build","--cppopts=-
D__GLASGOW_HASKELL__=610","--cppopts=-IC:
\\A\\install\\programming\\portaudio\\portaudio\\include","--output-dir=dist\\build","--
output=Sound\\PortAudio\\Base.hs",".\\Sound\\PortAudio\\Base.chs"])
c2hs.exe: does not exist
C:\Program Files\Haskell\bin\c2hs.exe returned ExitFailure 1
-- bang
To ascertain whether c2hs works at all, can you try to run it manually?
(cd to an appropriate directory,
cabal unpack portaudio
cd portaudio (or whatever, so that Base.chs is found via
.\Sound\PortAudio\Base.chs
md dist\build
c2hs.exe  --include=dist\build --cppopts=-D__GLASGOW_HASKELL__=610
--cppopts=-IC:
\A\install\programming\portaudio\portaudio\include --output-dir=dist\build
--
output=Sound\PortAudio\Base.hs .\Sound\PortAudio\Base.chs
)
If that works, the problem is somewhere in cabal, otherwise in c2hs, either
way, we'll
know more.
---------- Forwarded message ----------
From: M Xyz 
To: haskell-cafe@haskell.org, Andrew Coppin 
Date: Sat, 5 Dec 2009 16:34:52 -0800 (PST)
Subject: Re: [Haskell-cafe] HP + Gtk2hs?
--- On *Sat, 12/5/09, Andrew Coppin * wrote:
...
...
Hell, I even followed a C++ guide to Win32 programming and
managed to translate an "open a blank window" program to Haskell, and it
worked. Maybe somebody just needs to sit down and write a nice binding
for doing native GUI stuff under Win32?
Well there's
http://haskell.org/ghc/docs/latest/html/libraries/Win32/Graphics-Win32.htmlf... opening blank windows. ;)
This relates to my question a couple days ago about a good cross platform
2d library. I wonder why there isnt a Haskell library that follows in the
footsteps of Java's Swing - by that I mean, just have a very simple low
level way of opening a window, getting mouse clicks, and an abstracted
drawing layer... and make the GUIs with that. The GUIs are drawn and not OS
widgets. That's exactly why I was looking for something like Cairo. My
interest is in composable fudgets (stealing the word from fudgets).
This way every platform can share the same GUI library and HP can ship with
the minimal tools to open a window and draw on every system. Plus OS guis
are the wrong thing for Haskell. You need to retain the power to make better
abstractions.
---------- Forwarded message ----------
From: M Xyz 
To: haskell-cafe@haskell.org, Daniel Fischer 
Date: Sat, 5 Dec 2009 16:49:49 -0800 (PST)
Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
--- On *Sat, 12/5/09, Daniel Fischer * wrote:
If you have cpphs, hugs, jhc, greencard etc., it is probably something
about your
environment. If you don't have them, it's clear that they aren't found.
I don't know what those things are. I have nothing but what came with HP
other than installing c2hs today.
If that works, the problem is somewhere in cabal, otherwise in c2hs, either
way, we'll
know more.
Alright, I followed the instructions and everything was as you said. I
still get "c2hs.exe does not exist".
C:\A\install\programming\portaudio\haskell\portaudio-0.0.1>"C:\Program
Files\Has
kell\bin\c2hs.exe" --include=dist\build --cppopts=-D__GLASGOW_HASKELL__=610
--cp
popts=-IC:\A\install\programming\portaudio\portaudio\include
--output-dir=dist\b
uild --output=Sound\PortAudio\Base.hs .\Sound\PortAudio\Base.chs
c2hs.exe: does not exist
C:\A\install\programming\portaudio\haskell\portaudio-0.0.1>pause
Press any key to continue . . .
By the way, I have posted this problem to the c2hs mailing list in case
they have some insight.
---------- Forwarded message ----------
From: Daniel Fischer 
To: M Xyz 
Date: Sun, 6 Dec 2009 02:34:17 +0100
Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz:
I just had another idea.
dafis@linux-mkk1:~> c2hs -o memyself.hs memyself.chs
c2hs: does not exist
it's not that c2hs isn't found or something, c2hs doesn't find Base.chs!
Try installing from the unpacked sources (cd portaudio; cabal install) or
the old-
fashioned way:
cd portaudio-0.0.1
ghc --make Setup
./Setup configure --help
(choose your options, prefix, profiling, ...)
./Setup configure $OPTIONS
./Setup build
if all's well,
./Setup haddock
./Setup install
(dies for me with
dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei oder
Verzeichnisnicht gefunden
c2hs: Error during preprocessing custom header file
cabal: Error: some packages failed to install:
portaudio-0.0.1 failed during the building phase. The exception was:
exit: ExitFailure 1
because I don't have portaudio installed)
---------- Forwarded message ----------
From: john lask 
To: , 
Date: Sun, 6 Dec 2009 02:03:32 +0000
Subject: RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
I don't know whether this will help you but I just downloaded an built
the haskell portaudio package ... (I had a windows msvc build of
portaudio dll already) the process I used ... ghc 6.10.4, portaudio-19
make an import lib for ghc from dll:
pexports libpa19.dll > libpa19.def
dlltool --input-def libpa19.def --output-lib libpa19.a
edit the .cabal file or use command line flags
extra-Libraries: pa19
  extra-lib-dirs: c:\portaudio19\lib
  include-dirs:   c:\portaudio19\include
runghc setup configure
make sure you have cpp i.e. the c-preprocessor on your exe path,
otherwise you will get
'cpp' is not recognized as an internal or external command,
operable program or batch file.
c2hs.exe: Error during preprocessing custom header file
runghc setup build
builds ok ...??
...
From: daniel.is.fischer@web.de
To: functionallyharmonious@yahoo.com
Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
Date: Sun, 6 Dec 2009 02:34:17 +0100
CC: haskell-cafe@haskell.org
Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz:
I just had another idea.
dafis@linux-mkk1:~> c2hs -o memyself.hs memyself.chs
c2hs: does not exist
it's not that c2hs isn't found or something, c2hs doesn't find Base.chs!
Try installing from the unpacked sources (cd portaudio; cabal install) or
the old-
fashioned way:
cd portaudio-0.0.1
ghc --make Setup
./Setup configure --help
(choose your options, prefix, profiling, ...)
./Setup configure $OPTIONS
./Setup build
if all's well,
./Setup haddock
./Setup install
(dies for me with
dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei
oder
Verzeichnisnicht gefunden
c2hs: Error during preprocessing custom header file
cabal: Error: some packages failed to install:
portaudio-0.0.1 failed during the building phase. The exception was:
exit: ExitFailure 1
because I don't have portaudio installed)
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---------- Forwarded message ----------
From: Henning Thielemann 
To: Michael Snoyman 
Date: Sun, 06 Dec 2009 03:05:30 +0100 (CET)
Subject: Re: [Haskell-cafe] New Hackage category: Error Handling
On Sat, 5 Dec 2009, Henning Thielemann wrote:
On Sun, 6 Dec 2009, Michael Snoyman wrote:
...
I think there are plenty of examples like web servers. A text editor with
...
plugins? I
don't want to lose three hours worth of work just because some plugin
wasn't written
correctly. For many classes of programs, the distinction between error
and exception is
not only blurred, it's fully irrelevant. Harping on people every time
they use error in
the "wrong" sense seems unhelpful.
Hope my commenting on this subject doesn't become my own form of
*pedantry*.
In an earlier thread I have explained that one can consider a software
architecture as divided into levels. What is an error in one level (text
editor plugin, web server thread, operating system process) is an exception
in the next higher level (text editor, web server, shell respectively). This
doesn't reduce the importance to distinguish between errors and exceptions
within one level. All approaches so far that I have seen in Haskell just mix
exceptions and errors in an arbitrary way.
I have just written more details on this topic:
  http://www.haskell.org/haskellwiki/Error_vs._Exception
---------- Forwarded message ----------
From: M Xyz 
To: Daniel Fischer 
Date: Sat, 5 Dec 2009 18:08:07 -0800 (PST)
Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
--- On *Sat, 12/5/09, Daniel Fischer * wrote:
cd portaudio-0.0.1
ghc --make Setup
./Setup configure --help
(choose your options, prefix, profiling, ...)
./Setup configure $OPTIONS
./Setup build
Everything went well until "Setup build" which yielded our friend "c2hs.exe
does not exist".
C:\A\install\programming\portaudio\haskell\portaudio-0.0.1>ghc --make Setup
[1 of 1] Compiling Main             ( Setup.hs, Setup.o )
Linking Setup.exe ...
C:\A\install\programming\portaudio\haskell\portaudio-0.0.1>Setup configure
--hel
p
Usage: Setup configure [FLAGS]
Flags for configure: .......(edited out).................
C:\A\install\programming\portaudio\haskell\portaudio-0..0.1>Setup configure
--ext
ra-include-dirs="C:\A\install\programming\portaudio\portaudio\include"
--extra-l
ib-dirs="C:\A\install\programming\portaudio\portaudio\build\msvc\Win32\Release"
Configuring portaudio-0.0.1...
C:\A\install\programming\portaudio\haskell\portaudio-0.0.1>Setup build
Preprocessing library portaudio-0.0.1...
c2hs.exe: does not exist
---------- Forwarded message ----------
From: M Xyz 
To: daniel.is.fischer@web.de, john lask 
Date: Sat, 5 Dec 2009 18:17:29 -0800 (PST)
Subject: RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
I am going to give this a try. Thanks.
Where can I get the pexports and dlltool utilities?
Google yields:
http://www.emmestech.com/software/pexports-0.43/download_pexports.html
http://sourceware.org/binutils/
Are those correct?
--- On *Sat, 12/5/09, john lask * wrote:
From: john lask 
Subject: RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
To: daniel.is.fischer@web.de, functionallyharmonious@yahoo.com
Cc: haskell-cafe@haskell.org
Date: Saturday, December 5, 2009, 9:03 PM
I don't know whether this will help you but I just downloaded an built
the haskell portaudio package ... (I had a windows msvc build of
portaudio dll already) the process I used ... ghc 6.10.4, portaudio-19
make an import lib for ghc from dll:
pexports libpa19.dll > libpa19.def
dlltool --input-def libpa19.def --output-lib libpa19.a
edit the .cabal file or use command line flags
extra-Libraries: pa19
  extra-lib-dirs: c:\portaudio19\lib
  include-dirs:   c:\portaudio19\include
runghc setup configure
make sure you have cpp i.e. the c-preprocessor on your exe path,
otherwise you will get
'cpp' is not recognized as an internal or external command,
operable program or batch file.
c2hs.exe: Error during preprocessing custom header file
runghc setup build
builds ok ...??
...
From: daniel.is.fischer@web.de
To: functionallyharmonious@yahoo.com
Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
Date: Sun, 6 Dec 2009 02:34:17 +0100
CC: haskell-cafe@haskell.org
Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz:
I just had another idea.
dafis@linux-mkk1:~> c2hs -o memyself.hs memyself.chs
c2hs: does not exist
it's not that c2hs isn't found or something, c2hs doesn't find Base.chs!
Try installing from the unpacked sources (cd portaudio; cabal install) or
the old-
fashioned way:
cd portaudio-0.0.1
ghc --make Setup
./Setup configure --help
(choose your options, prefix, profiling, ...)
./Setup configure $OPTIONS
./Setup build
if all's well,
./Setup haddock
./Setup install
(dies for me with
dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei
oder
Verzeichnisnicht gefunden
c2hs: Error during preprocessing custom header file
cabal: Error: some packages failed to install:
portaudio-0.0.1 failed during the building phase. The exception was:
exit: ExitFailure 1
because I don't have portaudio installed)
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Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
------------------------------
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---------- Forwarded message ----------
From: M Xyz 
To: john lask , vanenkj@gmail.com
Date: Sat, 5 Dec 2009 19:47:04 -0800 (PST)
Subject: [Haskell-cafe] PortAudio library successfully built on Windows
John Lask,
The steps you enumerated below successfully built portaudio for me! Thank
you!
I wonder though, you said to rename the dll to libpa19.dll from
portaudio_x86.dll
and to change the .cabal entry from "extra-Libraries: portaudio" to
"extra-Libraries: pa19".
Since my .dll name and .cabal file entry were mismatched, was that what
could have been wrong all along? Was the creation of a .a file necessary?
I would delete the .a file and retry with libportaudio.dll but I won't push
my luck.
Now if I could just get Gtk2hs working now, I could be happy *and*
productive. :)
--- On *Sat, 12/5/09, john lask * wrote:
From: john lask 
Subject: RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
To: daniel.is.fischer@web.de, functionallyharmonious@yahoo.com
Cc: haskell-cafe@haskell.org
Date: Saturday, December 5, 2009, 9:03 PM
I don't know whether this will help you but I just downloaded an built
the haskell portaudio package ... (I had a windows msvc build of
portaudio dll already) the process I used ... ghc 6.10.4, portaudio-19
make an import lib for ghc from dll:
pexports libpa19.dll > libpa19.def
dlltool --input-def libpa19.def --output-lib libpa19.a
edit the .cabal file or use command line flags
extra-Libraries: pa19
  extra-lib-dirs: c:\portaudio19\lib
  include-dirs:   c:\portaudio19\include
runghc setup configure
make sure you have cpp i.e. the c-preprocessor on your exe path,
otherwise you will get
'cpp' is not recognized as an internal or external command,
operable program or batch file.
c2hs.exe: Error during preprocessing custom header file
runghc setup build
builds ok ...??
...
From: daniel.is.fischer@web.de
To: functionallyharmonious@yahoo.com
Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
Date: Sun, 6 Dec 2009 02:34:17 +0100
CC: haskell-cafe@haskell.org
Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz:
I just had another idea.
dafis@linux-mkk1:~> c2hs -o memyself.hs memyself.chs
c2hs: does not exist
it's not that c2hs isn't found or something, c2hs doesn't find Base.chs!
Try installing from the unpacked sources (cd portaudio; cabal install) or
the old-
fashioned way:
cd portaudio-0.0.1
ghc --make Setup
./Setup configure --help
(choose your options, prefix, profiling, ...)
./Setup configure $OPTIONS
./Setup build
if all's well,
./Setup haddock
./Setup install
(dies for me with
dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei
oder
Verzeichnisnicht gefunden
c2hs: Error during preprocessing custom header file
cabal: Error: some packages failed to install:
portaudio-0.0.1 failed during the building phase. The exception was:
exit: ExitFailure 1
because I don't have portaudio installed)
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
------------------------------
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---------- Forwarded message ----------
From: Michael Snoyman 
To: Haskell Cafe 
Date: Sun, 6 Dec 2009 07:04:46 +0200
Subject: [Haskell-cafe] When are undecidables ok?
I know this is basically a rewording of a previous e-mail, but I realized
this is the question I *really* wanted to ask.
We have this language extension UndecidableInstances (not to mention
OverlappingInstances), which seem to divide the Haskell camp into two
factions:
* Hey, GHC said to turn on this flag. Ok!
* Undecidables are the devil!
I get the feeling the truth lies in the middle. As I understand it (please
correct me if I am wrong), the problem with undecidables is that they can
create non-terminating instances. However, for certain cases the programmer
should be able to prove to him/herself that the instances will terminate. My
question is: how can you make such a proof?
I've had to cases in particular that made me want undecidables. Both of
them, IMO, could be solved by creating new extensions to GHC which would not
require undecidables. Nonetheless, for now we only have undecidables at our
disposal. The examples are:
* Context synonyms (eg, MonadFailure = Monad + Failure).
* Subclass function defaulting
For an example of the second, a nifty definition of Monad would be:
...
...
= ...
  return ...
class Applicative m => Monad m where
  pure = return
  (<*>) = ap
  fmap = liftM
Of course, neither of these is possible in Haskell, so we can use
undecidables. How can a programmer prove that a set of instances is, in
fact, safe? And if they make a mistake and right a bad set of
undecidable/overlapping instances, what's the worst case scenario? Is it a
compile-time or run-time error*?
Michael
* Yes, I mean error.
...
I know this is basically a rewording of a previous e-mail, but I realized
this is the question I *really* wanted to ask.
We have this language extension UndecidableInstances (not to mention
OverlappingInstances), which seem to divide the Haskell camp into two
factions:
* Hey, GHC said to turn on this flag. Ok!
* Undecidables are the devil!
I get the feeling the truth lies in the middle. As I understand it
(please
correct me if I am wrong), the problem with undecidables is that they can
create non-terminating instances. However, for certain cases the
---------- Forwarded message ----------
From: Luke Palmer 
To: Michael Snoyman 
Date: Sat, 5 Dec 2009 22:36:43 -0700
Subject: Re: [Haskell-cafe] When are undecidables ok?
On Sat, Dec 5, 2009 at 10:04 PM, Michael Snoyman 
wrote:
programmer
...
should be able to prove to him/herself that the instances will terminate.
My
question is: how can you make such a proof?
Well, the reasoning for the "devil" camp (which I admit to being
firmly in[1]) is that such proofs must rely on the algorithm the
compiler uses to resolve instances.  You might be able to prove it,
but the proof is necessarily only valid for (possibly current versions
of) GHC.  The typeclass resolution algorithm is not in the report, and
there are several conceivable ways of of going about it.
So it is fine to use them if you are okay with making your code
unportable and future-brittle. I am typically against the mere
existence of code that that is future-brittle, because it encourages
compiler authors not to innovate  (and by that token, unportable too,
because it discourages compiler competition).
Luke
[1]
http://lukepalmer.wordpress.com/2008/04/08/stop-using-undecidable-instances/
---------- Forwarded message ----------
From: Michael Snoyman 
To: Luke Palmer 
Date: Sun, 6 Dec 2009 08:20:09 +0200
Subject: Re: [Haskell-cafe] When are undecidables ok?
On Sun, Dec 6, 2009 at 7:36 AM, Luke Palmer  wrote:
...
...
I know this is basically a rewording of a previous e-mail, but I
realized
this is the question I *really* wanted to ask.
We have this language extension UndecidableInstances (not to mention
OverlappingInstances), which seem to divide the Haskell camp into two
factions:
* Hey, GHC said to turn on this flag. Ok!
* Undecidables are the devil!
I get the feeling the truth lies in the middle. As I understand it
(please
correct me if I am wrong), the problem with undecidables is that they
can
create non-terminating instances. However, for certain cases the
On Sat, Dec 5, 2009 at 10:04 PM, Michael Snoyman 
wrote:
programmer
...
should be able to prove to him/herself that the instances will
terminate. My
question is: how can you make such a proof?
Well, the reasoning for the "devil" camp (which I admit to being
firmly in[1]) is that such proofs must rely on the algorithm the
compiler uses to resolve instances.  You might be able to prove it,
but the proof is necessarily only valid for (possibly current versions
of) GHC.  The typeclass resolution algorithm is not in the report, and
there are several conceivable ways of of going about it.
So it is fine to use them if you are okay with making your code
unportable and future-brittle. I am typically against the mere
existence of code that that is future-brittle, because it encourages
compiler authors not to innovate  (and by that token, unportable too,
because it discourages compiler competition).
Luke
[1]
http://lukepalmer.wordpress.com/2008/04/08/stop-using-undecidable-instances/
So in that case, perhaps the compiler authors can give us some ideas as to
when it's safe to use undecidables? Seems like we should go straight to the
horse's mouth.
Michael
---------- Forwarded message ----------
From: "Ariel J. Birnbaum" 
To: Gregory Crosswhite 
Date: Sun, 06 Dec 2009 08:34:16 +0200
Subject: Re: [Haskell-cafe] ANNOUNCE: error-message
...
In particular, the motivation for this package was that I have written
a build system, and I wanted to collect as many errors in the build as
possible and show them all to the user at once.
YMMV, but at least for me a deluge of errors is less helpful than a
short list I can fix quickly, then try again. Often by fixing one error
from the list a sizeable portion of the rest just vanish (I forget the
English term for that kind of error).
(In before "you can use sth like quickfix to go through the first few
errors and compile again whenever you feel like it".)
--
Ariel J. Birnbaum
---------- Forwarded message ----------
From: Eugene Kirpichov 
To: Stefan Holdermans 
Date: Sun, 6 Dec 2009 09:42:34 +0300
Subject: Re: [Haskell-cafe] What is the rank of a polymorphic type?
2009/12/6 Stefan Holdermans :
...
Eugene,
...
1) Does there exist an authoritative source saying the same? Not that
I'm doubting, just supposing that the source would have other
interesting information, too :)
You may want to have a look at the already mentioned JFP-article by
Peyton
Jones et al. and perhaps the work of Kfoury and Wells.
...
2) Is it true that rank (forall a . a, forall a . a) == 0 ?
No, for pairs one takes the maximum of the constituent types. So, here
you'd
get rank 1.
Note that this is an impredicative type, which is yet another extension
of
the standard Hindley-Milner typing discipline.
OK, thanks.
However, isn't the type (forall a . a) -> String impredicative because
it instantiates a type variable of the type constructor (->) p q with
p = forall a . a?
...
Cheers,
Stefan
...
...
--
Eugene Kirpichov
Web IR developer, market.yandex.ru
---------- Forwarded message ----------
From: Benjamin L.Russell 
To: haskell-cafe@haskell.org
Date: Sun, 06 Dec 2009 16:14:06 +0900
Subject: [Haskell-cafe] Re: universal binary version of Haskell Platform?
On Thu, 03 Dec 2009 10:52:35 +0000, Duncan Coutts
 wrote:
...
[...]
There no binary platform installer for OSX PPC. You'll have to grab
ghc-6.10.4 for PPC from the ghc download page and then install the
platform from the generic source tarball.
Ah, that's too bad.  That means that I won't be able to invoke GHC
outside of the Terminal application by default, and that even if I
create a Darwin shell script and alias to invoke it from Aqua, the
icon for that shell script will only be generic by default.  I'd
rather click on an application icon in the Dock.
...
If you'd like to help us next time to make a platform binary for PPC
then that'd be great. I don't think we have the setup to make universal
binaries but it should be possible to make a PPC build if we have a
volunteer.
Sure, barring job-related time constraints, I'd be happy to volunteer.
My Mac just went out of service because of a hardware problem with the
memory, so I'm order new replacement RAM this weekend.  As soon as
that arrives and I install it, the problem should be resolved.
What should I do?
-- Benjamin L. Russell
---------- Forwarded message ----------
From: Dan Doel 
To: haskell-cafe@haskell.org
Date: Sun, 6 Dec 2009 02:48:09 -0500
Subject: Re: [Haskell-cafe] What is the rank of a polymorphic type?
On Sunday 06 December 2009 1:42:34 am Eugene Kirpichov wrote:
...
OK, thanks.
However, isn't the type (forall a . a) -> String impredicative because
it instantiates a type variable of the type constructor (->) p q with
p = forall a . a?
There's probably no clear cut answer to this independent of how you think
of
(->). For instance, if we explain the Haskell type system by way of a pure
type system, (->) is a special case of a pi type, which looks like:
pi x : k. t
where any xs in t are bound by the pi. We then have:
p -> q          = pi _ : p. q
 forall a : k. b = pi a : k. b
pi types are given types by sets of rules, which look like triples. If
(s,t,u)
is a rule, then:
G |- k : s    G, a : k |- b : t
 -------------------------------
     G |- (pi a : k. b) : u
is the corresponding typing rule. Type systems like Haskell's are commonly
thought of in terms of the lambda cube, which has constant sorts * and [],
with * : []. The rule (*,*,*) gives you ordinary functions. (*,[],[]) gives
you dependent types, so that's out.
([],*,*) is an impredicative rule for polymorphism. This says that, for
instance:
forall a. a -> a = (pi a : *. pi _ : a. a) : *
because (pi _ : a. a) : * if a : *, by the (*,*,*) rule, and then we apply
the
impredicative rule for the universal quantification. One could also use the
predicative rule ([],*,[]), which would result in forall a. a -> a having
type
[].
However, Haskell also has arbitrarily higher-order types. This is given by
the
rule ([],[],[]), which allows expressions like:
(* -> *) -> * = pi _ : (pi _ : *. *). *
This type system is called F_omega, while just the ([],*,?) rule is known
as
F_2.
However, the F_omega rule also allows for arbitrary rank polymorphism even
with the predicative universal quantifier rule above (predicative F_2
allows a
little, but it's very limited*). For instance, the higher rank type:
forall a. (forall b. b) -> a
checks thusly:
(forall b. b)                  : [] via ([],*,[])
 ((forall b. b) -> a)           : [] via ([],*,[])
 (forall a. (forall b. b) -> a) : [] via ([],[],[])
Data types, by contrast, have kinds like * -> *, so using say,
Maybe (forall a. a -> a)
genuinely relies on the impredicative rule. GHC's type system isn't exactly
set up in this way, but (->) is similarly special in that it somehow isn't
quite just another type constructor with kind * -> * -> * (or even whatever
special kinds GHC uses to support unboxed values and such).
Hope that wasn't too confusing. :)
-- Dan
* Predicative F_2 will essentially allow one universal quantifier somewhere
in
the type. This can be:
forall a. a -> a
or it can be:
(((forall a. a) -> T) -> U) -> V
for T, U and V of kind * (the only kind in F_2), which is a rank-4 type. It
doesn't allow:
forall a b. a -> b
even, because the inner (forall b. a -> b) : [], so adding the forall a
requires the F_omega rule.
Predicative F_2 and F_w also blow up with quantification on the right of an
arrow, because it looks like the rule for dependent types:
T -> (forall a. a)
T : *, (forall a. a) : []
so the rule (*,[],[]) would be invoked.
GHC doesn't have this sort of hierarchy, and so doesn't have these sorts of
weird cases, despite being predicative of a sort. Instead it distinguishes
somehow between monotypes ([Float], String -> Int, a -> b) and polytypes
(forall a. a, ...), although it doesn't really display the difference.
Quantifiers are only supposed to range over kinds that classify monotypes
(or
monotype constructors), which keeps the predicativity (although, even this
gets fudged some: If I have forall a. a -> a, I can instantiate a to the
polytype forall a. a -> a with rank-n polymorphism, because it only seems
to
worry about the validity of the resulting type, and (->) is special; by
contrast, the same cannot be said for forall a. Maybe a, because Maybe
genuinely only accepts monotypes without -XImpredicativeTypes).
---------- Forwarded message ----------
From: Bulat Ziganshin 
To: Andrew Coppin 
Date: Sun, 6 Dec 2009 11:13:21 +0300
Subject: Re[2]: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
Hello Andrew,
Sunday, December 6, 2009, 1:09:18 AM, you wrote:
...
Maybe once I get hired by some financial modelling consultants and get
paid shedloads of money to write Haskell all day, I'll be able to afford
a Mac. But until then...
with such attitude you will never be hired by financial sector. try
instead:
mac? great! windows? i love it! unix? i've used it since 60's
--
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com
---------- Forwarded message ----------
From: Heinrich Apfelmus 
To: haskell-cafe@haskell.org
Date: Sun, 06 Dec 2009 11:28:25 +0100
Subject: [Haskell-cafe] Re: universal binary version of Haskell Platform?
Benjamin L.Russell wrote:
...
Ah, that's too bad.  That means that I won't be able to invoke GHC
outside of the Terminal application by default, and that even if I
create a Darwin shell script and alias to invoke it from Aqua, the
icon for that shell script will only be generic by default.  I'd
rather click on an application icon in the Dock.
You can write an applescript similar to
Open Terminal Here
   from http://www.entropy.ch/software/applescript/
and endow it with a custom icon.
Regards,
Heinrich Apfelmus
--
http://apfelmus.nfshost.com
---------- Forwarded message ----------
From: Andrew Coppin 
To: haskell-cafe@haskell.org
Date: Sun, 06 Dec 2009 13:05:19 +0000
Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound
card?
Bulat Ziganshin wrote:
...
Hello Andrew,
Sunday, December 6, 2009, 1:09:18 AM, you wrote:
...
Maybe once I get hired by some financial modelling consultants and get
paid shedloads of money to write Haskell all day, I'll be able to afford
a Mac. But until then...
with such attitude you will never be hired by financial sector. try
instead:
mac? great! windows? i love it! unix? i've used it since 60's
That's OK. I'm reasonably sure I will never get hired by the financial
sector /anyway/. :-(
---------- Forwarded message ----------
From: Andrew Coppin 
To: haskell-cafe@haskell.org
Date: Sun, 06 Dec 2009 13:18:59 +0000
Subject: Re: [Haskell-cafe] binding to C libraries on Windows was Low Level
Audio - Writing bytes to the sound card?
john lask wrote:
...
I think there are some misapprehensions here:-
Many haskell packages binding to c libraries will compile with ghc
without problems on windows - without cygwin, without mingw/msys system.
OK, well I haven't tried building every C binding on all of Hackage, just a
few of them. So far none of them have worked. (Including wxHaskell, SDL, one
of the database packages, etc.) It's got to the point where I've simply
given up trying. Most such packages just don't seem to work on Windows, and
nobody on the mailing lists or on IRC has any clue why. (I guess because few
people in the Haskell community use Windows and understand how it's supposed
to work.)
Some such packages build "out of the box" on windows, like the zlib
...
package which contains the c source for the c zlib library. GHC is able
to compile and build this packages without any other c
compiler/libraries/unix emulators etc because ghc itself contains part
of the gcc c compiler tool chain and comes with all c standard headers,
c++ headers and c/c++ runtime libraries.
Yes, I realised long ago that GHC uses GCC and other GNU build tools.
(Presumably this makes porting to Windows far easier.) More recently I
realised that it also includes a surprisingly large set of header files,
seemingly including the entire Win32 API, which is interesting.
There
...
is only one gotch-ya - you need to have a import library for the gcc
tool chain (thats what ghc uses) i.e. a ".a" library and not the native
windows ".LIB" import library.
They're different?? o_O
Oh. Suddenly several things seem clearer...
If you don't have ".a" import library
...
but have the dll then the '.a' import library be built for any dll
relativley easily.
Any idea how?
the bigest problem hamperring cleaner builds of haskell packages on
...
windows is the lack of any standardised scheme for the installation of
c-libraries and header files (and of course the availability of a
suitable build of the library).
Isn't one of Cabal's jobs to figure out where stuff is? Can't we get Cabal
on Windows to say "hey, I need to find foo.h, you know where that is?" Or
something like that?
Another problem hampering the install of haskell packages on windows is
...
the use of the unix autoconf build system (./configure)   - package
writters note!
Heh. I found one Wiki page once describing how to set up a Cabal package.
When it started talking about how to integrate Automake, I hung my head is
dispair. (I believe the page in question is fixed now. But a lot of package
authors seem to assume that everybody just uses Unix of some kind...)
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