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Today's Topics:
1. Re: foldl by foldr (Matt Andrew)
2. diagrams installation trouble (Scott N. Walck)
----------------------------------------------------------------------
Message: 1
Date: Mon, 17 May 2010 12:14:01 +1000
From: Matt Andrew <[email protected]>
Subject: Re: [Haskell-beginners] foldl by foldr
To: [email protected]
Message-ID: <m2y6fjp95i.wl%[email protected]>
Content-Type: text/plain; charset=US-ASCII
Thanks everyone for all the help: I've now been able to understand the function
and have a better understanding of partial application to boot.
Appreciate it,
Matt Andrew
At Fri, 14 May 2010 11:43:03 -0700,
John Bender wrote:
>
> [1 <multipart/alternative (7bit)>]
> [1.1 <text/plain; ISO-8859-1 (7bit)>]
> Matt,
>
> I was having issues with the very same problem not too long ago and I wrote
> a blog post about how it illustrates the power of partial application.
>
> http://nickelcode.com/2009/04/12/haskell-learnings/
>
> Sorry for the blog plug, I just didn't see any reason to copy and paste the
> content. I make no claims about the quality of my writing but it does
> include some basic expansions of the execution/thunks for understanding.
>
> Best
>
> On Fri, May 14, 2010 at 6:58 AM, Brent Yorgey <[email protected]>wrote:
>
> > On Fri, May 14, 2010 at 12:29:01PM +1000, Matt Andrew wrote:
> > >
> > > The thing I am having trouble understanding is what the 'id'
> > > function is doing in a function that expects 3 arguments and is
> > > given 4 (foldr).
> >
> > "Number of arguments" in Haskell is a red herring. In fact, every
> > Haskell function takes exactly *one* argument. Functions which appear
> > to "take more than one argument" are really functions which take one
> > argument and return another function (which takes the next argument,
> > and so on). That's why the type of a "multi-argument" function is written
> > like
> >
> > X -> Y -> Z -> ...
> >
> > which can also be written more explicitly as
> >
> > X -> (Y -> (Z -> ...))
> >
> > Polymorphic functions (like foldr) can also be deceiving as far as
> > "number of arguments" goes. For example, consider id:
> >
> > id :: a -> a
> >
> > Looks like this takes only one argument, right? Well, what if a = (Int ->
> > Int):
> >
> > id :: (Int -> Int) -> (Int -> Int)
> >
> > which can also be written
> >
> > id :: (Int -> Int) -> Int -> Int
> >
> > so now it looks like id "takes two arguments" -- an (Int -> Int)
> > function, and an Int. Of course, the real answer is that id always
> > takes exactly one argument, just like any other function; but
> > sometimes that argument may itself be a function, in which case
> > the result can be applied to additional argument(s).
> >
> > -Brent
> > _______________________________________________
> > Beginners mailing list
> > [email protected]
> > http://www.haskell.org/mailman/listinfo/beginners
> >
> [1.2 <text/html; ISO-8859-1 (quoted-printable)>]
>
> [2 <text/plain; us-ascii (7bit)>]
> _______________________________________________
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------------------------------
Message: 2
Date: Mon, 17 May 2010 12:06:29 -0400
From: "Scott N. Walck" <[email protected]>
Subject: [Haskell-beginners] diagrams installation trouble
To: [email protected]
Message-ID: <20100517160629.gb19...@walck-nsf>
Content-Type: text/plain; charset=us-ascii
Hi folks,
I'm trying to install Brent Yorgey's diagrams library. I'm having
trouble getting the Haskell bindings to the Cairo library installed
correctly and/or visible.
As you can see below, I have the Haskell Cairo stuff installed at
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1
I did this with something like
$ sudo aptitude install libghc6-cairo-dev
In other words, I used the ubuntu package system to install this.
You can also see that ghc-pkg does not see this installation.
I thought I might be able to fix the problem by registering
these packages with 'ghc-pkg register', but I can't get that
to work.
Finally (and this is not shown below) I tried to compile gtk2hs from
source. I seem to have had a successful './configure' step, but then
I fail at the 'make' step, for a similar reason. The system can't
find the cairo and similar files at /usr/lib/haskell-packages
One more point about my system might be important.
I installed GHC 6.10 using the ubuntu installer, then
compiled 6.12 from source, then installed the most recent
haskell-platform.
I would greatly appreciate any help you all could provide.
Thanks,
Scott
wa...@walck-nsf:~/computer/haskell/Yorgey$ cd diagrams-new/
wa...@walck-nsf:~/computer/haskell/Yorgey/diagrams-new$ runhaskell Setup.lhs
configure
Configuring diagrams-0.2.9...
Setup.lhs: At least the following dependencies are missing:
cairo >=0.9 && <0.11, colour >=2.2.1 && <2.4, containers ==0.2.*
wa...@walck-nsf:~/computer/haskell/Yorgey/diagrams-new$ runhaskell Setup.lhs
configure --user
Configuring diagrams-0.2.9...
Setup.lhs: At least the following dependencies are missing:
cairo >=0.9 && <0.11, containers ==0.2.*
wa...@walck-nsf:~/computer/haskell/Yorgey/diagrams-new$ ghc-pkg list
/usr/local/lib/ghc-6.12.1/package.conf.d:
Cabal-1.8.0.2
GLUT-2.1.2.1
HTTP-4000.0.9
HUnit-1.2.2.1
OpenGL-2.2.3.0
QuickCheck-2.1.0.3
array-0.3.0.0
base-3.0.3.2
base-4.2.0.0
bin-package-db-0.0.0.0
bytestring-0.9.1.5
cgi-3001.1.7.2
containers-0.3.0.0
deepseq-1.1.0.0
directory-1.0.1.0
(dph-base-0.4.0)
(dph-par-0.4.0)
(dph-prim-interface-0.4.0)
(dph-prim-par-0.4.0)
(dph-prim-seq-0.4.0)
(dph-seq-0.4.0)
extensible-exceptions-0.1.1.1
ffi-1.0
fgl-5.4.2.2
filepath-1.1.0.3
(ghc-6.12.1)
(ghc-binary-0.5.0.2)
ghc-prim-0.2.0.0
haskell-platform-2010.1.0.0
haskell-src-1.0.1.3
haskell98-1.0.1.1
hpc-0.5.0.4
html-1.0.1.2
integer-gmp-0.2.0.0
mtl-1.1.0.2
network-2.2.1.7
old-locale-1.0.0.2
old-time-1.0.0.3
parallel-2.2.0.1
parsec-2.1.0.1
pretty-1.0.1.1
process-1.0.1.2
random-1.0.0.2
regex-base-0.93.1
regex-compat-0.92
regex-posix-0.94.1
rts-1.0
stm-2.1.1.2
syb-0.1.0.2
template-haskell-2.4.0.0
time-1.1.4
unix-2.4.0.0
utf8-string-0.3.4
xhtml-3000.2.0.1
zlib-0.5.2.0
/home/walck/.ghc/x86_64-linux-6.12.1/package.conf.d:
GLFW-0.4.2
binary-0.5.0.2
colour-2.3.1
darcs-2.4.1
dataenc-0.13.0.2
dimensional-0.8
gnuplot-0.3.4
hashed-storage-0.4.11
haskeline-0.6.2.2
mmap-0.4.1
monoid-transformer-0.0.2
non-negative-0.0.5.1
numeric-prelude-0.1.3.4
numtype-1.0
storable-record-0.0.2.2
terminfo-0.3.1.2
transformers-0.2.1.0
utf8-string-0.3.6
utility-ht-0.0.5.1
wa...@walck-nsf:~/computer/haskell/Yorgey/diagrams-new$ dpkg -L
libghc6-cairo-dev
/.
/usr
/usr/share
/usr/share/doc
/usr/share/doc/libghc6-cairo-dev
/usr/share/doc/libghc6-cairo-dev/changelog.gz
/usr/share/doc/libghc6-cairo-dev/copyright
/usr/share/doc/libghc6-cairo-dev/changelog.Debian.gz
/usr/lib
/usr/lib/haskell-packages
/usr/lib/haskell-packages/ghc6
/usr/lib/haskell-packages/ghc6/lib
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/cairo.package.conf
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/libHScairo.a
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/HScairo.o
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Drawing
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Drawing/Cairo.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Drawing/Paths.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Drawing/Patterns.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Drawing/Text.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Drawing/Transformations.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Fonts
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Fonts/FontOptions.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Surfaces
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Surfaces/Image.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Surfaces/PDF.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Surfaces/PNG.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Surfaces/PS.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Surfaces/SVG.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Surfaces/Surface.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal/Utilities.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Matrix.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Types.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo/Internal.hi
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/imports/Graphics/Rendering/Cairo.hi
wa...@walck-nsf:~/computer/haskell/Yorgey/diagrams-new$ ls -l
/usr/lib/haskell-packages/ghc6/lib/
total 20
drwxr-xr-x 3 root root 4096 2010-05-04 08:25 cairo-0.10.1
drwxr-xr-x 3 root root 4096 2010-05-04 16:48 curl-1.3.5
drwxr-xr-x 4 root root 4096 2010-05-04 08:25 glib-0.10.1
drwxr-xr-x 3 root root 4096 2010-05-04 16:00 gtk-0.10.1
drwxr-xr-x 3 root root 4096 2010-05-04 08:25 mtl-1.1.0.2
wa...@walck-nsf:~/computer/haskell/Yorgey/diagrams-new$ ghc-pkg register
/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/cairo.package.conf
Reading package info from
"/usr/lib/haskell-packages/ghc6/lib/cairo-0.10.1/cairo.package.conf" ... done.
cairo-0.10.1: missing id field
cairo-0.10.1: dependency "base-4.1.0.0" doesn't exist (use --force to override)
cairo-0.10.1: dependency "mtl-1.1.0.2" doesn't exist (use --force to override)
cairo-0.10.1: dependency "glib-0.10.1" doesn't exist (use --force to override)
cairo-0.10.1: dependency "bytestring-0.9.1.4" doesn't exist (use --force to
override)
wa...@walck-nsf:~/computer/haskell/Yorgey/diagrams-new$ ghc-pkg register
/usr/lib/haskell-packages/ghc6/lib/glib-0.10.1/glib.package.conf
Reading package info from
"/usr/lib/haskell-packages/ghc6/lib/glib-0.10.1/glib.package.conf" ... done.
glib-0.10.1: missing id field
glib-0.10.1: dependency "base-4.1.0.0" doesn't exist (use --force to override)
wa...@walck-nsf:~/computer/haskell/Yorgey/diagrams-new$
--
Scott N. Walck
Associate Professor of Physics
Lebanon Valley College
Annville, PA 17003
phone: 717-867-6153
fax: 717-867-6075
email: [email protected]
------------------------------
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