{-
This message presents a typed final-tagless HOAS interpreter for
linear lambda calculus (LLC), which makes use of type families and
datatype promotion. This code is inspired by Oleg's LLC interpreter
using deBruijn indices
(http://okmij.org/ftp/tagless-final/course/LinearLC.hs).
The basic
Here is an haste of the original message since it seems like the
formatting was lost.
http://hpaste.org/76082
sorry about that,
Jeff
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Hello,
I have a sample file (attached) which I cannot read into Text:
Prelude Control.Applicative Data.Text.IO.readFile foo
*** Exception: utf8.txt: hGetContents: invalid argument (invalid
byte sequence)
Prelude Control.Applicative Data.Text.Encoding.decodeUtf8 $
This message shows how to slightly reformulate HLists (and other type-level
things) to get better type-checking and more informative error messages. The
technique is interesting in that it uses GADTs and functional dependencies and
seems to not be implementable with associated type synonyms. It
Hello,
One major thing I haven't seen explicitly mentioned yet in this thread
is tail recursion. You have to write tail recursively in OCaml (or any
strict language) or you will blow the stack. While tail recursion is
often wrong (in terms of efficiency) in Haskell, it is always right in
OCaml.
Hello,
To let the type checker do some work for you, without getting all the
way into the territory of the dimensional package, you can use
newtypes and a Units class with methods for wrapping and unwrapping
Doubles; we use this approach at work and find it strikes a nice
balance between useful
Couldn't resist taking the bait...
Well, continuations come from Scheme, and by and large, they are usually
used in languages like Scheme (i.e. PLT web server), or Smalltalk (Seaside
web server),
For a fuller history of continuatios, please see The Discoveries of
Continuations by John
Hello,
The HList paper (http://homepages.cwi.nl/~ralf/HList/) presents a
reasonable general type level equality (though it requires GHC). The
paper also describes some other implementations including the
interpretation of types as type-level nats.
-Jeff
On Mon, Aug 25, 2008 at 8:11 PM, Marc
Hello,
Manual Typeable deriving should probably be disabled :-)
There are legitimate reasons to define your own Typeable instances.
Since Typeable already contains all the machinery you need to type a
standard functional language, it is nice to just add Typeable
instances when defining your own
Hello,
Is it possible in Haskell + GHC extensions to use reflection
techniques to determine typeclass membership? I'm thinking of things
like the following:
I think the short answer is not in general; i.e. I don't think there is any
way to access the members of an arbitrary typeclass (but
Hello,
Data.Typeable gives you most of what you want except for access to
function bodies.
-Jeff
On Tue, Mar 11, 2008 at 6:17 AM, Martin Hofmann
[EMAIL PROTECTED] wrote:
I am trying to port a programme written in Maude, which is a reflective
language based on rewriting logic (
Hello,
Here are the essential details...
Location: NYC
Industry: finance
Salary: enough to live comfortably in Manhattan
Hard Requirements:
Must be able to work in the USA (we can't get you a worker's visa).
Must be an expert level Haskell user; must be comfortable with
monads,
Hello,
Didn't someone already prove all monads can be implemented in terms
of Cont?
Cont and StateT, wasn't it?
And the schemers have no choice about running in StateT :)
You sure? I want to see the proof :)
I think this is referring to Andrzej Filinski's paper Representing
Layered
Hello,
When building the latest hdbc-odbc (1.1.2.0) on a linux box with
ghc6.6.1, I get the following warnings:
[7 of 7] Compiling Database.HDBC.ODBC ( Database/HDBC/ODBC.hs,
dist/build/Database/HDBC/ODBC.o )
hdbc-odbc-helper.c: In function รข:
hdbc-odbc-helper.c:131:0:
Hello,
It's probably easiest to think of composition as a function which
takes two arguments (both functions), (g :: b - c) and (f :: a - b),
and returns a new function of type a - c. We could write this
explicitly as
composition :: (b - c, a - b) - a - c
composition (g,f) = \x - g (f x)
Hello,
I have heard from a number of people that this behavior is not very
newbie-friendly. I can see how that is true. I have an API revision
coming anyway, so perhaps this is the time to referse the default
laziness of HDBC calls (there would be a '-version of everything with
laziness
Hello,
I don't mean to hijack the thread. Does anyone have experience in
using either HDBC or HSQL with Microsoft SQL server?
I use HDBC with MS SQL Server, Sybase, and Oracle. I use the ODBC
bindings. I am running on both a windows XP machine and a linux
machine (although I haven't been able
Hello,
Would you go as far to say that when new programmers ask which database
binding to use, we should _recommend_ HDBC then? (As we do gtk2hs, for
the gui libraries).
I'm not sure about this. Although I didn't extensively compare HSQL
and HDBC, I got the impression that they offered
Hello,
I am experimenting with type-level HList based programming.
The Apply class:
class Apply f a r | f a - r where
apply :: f - a - r
apply = undefined -- In case we use Apply for
-- type-level computations only
-- Normal function
Hello,
I managed to write a function, which ghc accepts, for which ghc
rejects it's own type signature. I remember seeing a thread about this
sometime in the last year or so, but I can't seem to find it. Does
anyone remember this thread?
thanks,
Jeff
Hello,
I finally found the thread I was looking for:
http://www.haskell.org/pipermail/haskell-cafe/2006-December/020481.html
Sorry for the noise.
-Jeff
On 7/14/07, jeff p [EMAIL PROTECTED] wrote:
Hello,
I managed to write a function, which ghc accepts, for which ghc
rejects it's own
Hello,
Since there were no replies about CS related category programs, I
thought I'd point out a few notable places, and people, for category
theory oriented CS.
University of Pennsylvania has Peter Freyd in the math department,
though he often collaborates with CS people.
Carnegie Mellon
Hello,
If -fvia-C fixes your problem, then your code has a bug, strictly speaking. If
your foreign call requires some information from a header file, then the right
way to call it is by making a small C wrapper function and calling that.
I tried to do this but couldn't. I could get GHC to
Hello,
No, it sounds like you're using the wrong import syntax.
That linker warning is a dead givaway you should be using ccall, not
stdcall.
Ok. I just tried changing this and now things work fairly well. I
thought stdcall was the correct syntax for windows.
This seems like a strange state
Hello,
In case anyone else finds this useful...
My linking problem was finally resolved by using the -fvia-C flag
when compiling with ghc.
Thanks to Stefan O'Rear who pointed out the possibility and wrote:
Does using -fvia-C help at all? The C compiler understands header
files and is
Hello,
I just moved to ghc-6.6.1and was wondering if there is an automatic
way to update the various packages I had installed previously.
thanks,
jeff
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Hello,
Can anyone give me some tips concerning the following error:
myPrompt ghc --make -fffi f.hs -l mylib.lib
ghc --make -fffi f.hs -l mylib.lib
[1 of 1] Compiling Main ( f.hs, f.o )
Linking f.exe ...
d:\ghc\ghc6.6\gcc-lib\ld.exe: cannot find -l-Ld:/ghc/ghc6.6
Hello,
On 5/29/07, Brandon S. Allbery KF8NH [EMAIL PROTECTED] wrote:
On May 29, 2007, at 23:01 , jeff p wrote:
myPrompt ghc --make -fffi f.hs -l mylib.lib
For historical reasons, you can't have a space between the -l and the
library name. It's inserting an empty library name
Hello,
Thanks for the tips. I've gotten to the point where linking fails on
an undefined reference. The strange thing about this is that when I
make a C program to call the library function and compile with:
myPrompt gcc f.c mylib.lib
everything works fine. I think ghc is using it's own
Hello,
No, but ghc does pass a lot of funny flags...
Double check ccall v. stdcall in the import declaration. That bites a
lot of people on Windows.
My import statement originally looked like:
foreign import ccall mylib.h myFun my_fun :: CDouble - IO (Ptr CDouble)
and my original
Hello,
On 4/15/07, David Powers [EMAIL PROTECTED] wrote:
so... this is likely a question based on serious misunderstandings, but can
anyone help me understand the exact mechanism by which monads enforce
sequencing?
Monads do not enforce sequencing.
In general, data dependencies enforce
{
Hello,
Here is a variation on Claus' code which returns an Either type
rather than fails with error. This could be further generalized to use
any instance of MonadError, rather than Either.
-Jeff
}
import Control.Monad.Error
financial_output :: String - String - String - String -
Hello,
I think that whole program flow thing is something you get used to. In
true, pure functional programming (i.e. Haskell) program flow is a
meaningless term, basically. Haskell is a declarative language, not an
imperative one. You have to learn to give up that control and trust the
Hello,
On 1/23/07, Bryan O'Sullivan [EMAIL PROTECTED] wrote:
Tim Docker wrote:
I'm not aware of any ongoing haskell work in finance, other that
some private work being done by Alain Cremieux, reported in the HCAR.
Lennart Augustsson works for Credit Suisse, using a Haskell DSEL to
generate
Hello,
breakUp s
| L.null s = []
| otherwise = h:(breakUp r) where
(h,r) = L.splitAt 72 s
Running this on the 2G file blows up the stack pretty quickly, taking
the first 1 million records (there are 20M of them) with a big stack
parameter gives about 25%
Hello,
Alternatively, I can wrap all of the state up into a single universal
structure that holds everything I will ever need at every step, but
doing so seems to me to fly in the face of strong typing; at the early
stages of processing, the structure will have holes in it that don't
contain
Hello,
The HList paper gives a type cast:
class TypeCast a b | a - b, b-a where typeCast :: a - b
class TypeCast' t a b | t a - b, t b - a where typeCast' :: t-a-b
class TypeCast'' t a b | t a - b, t b - a where typeCast'' :: t-a-b
instance TypeCast' () a b = TypeCast a b
Hello,
Thanks for the response.
Is it possible to write a class which checks to see if two given type
arguments are unifiable?
This will probably help:
http://www.haskell.org/pipermail/haskell-cafe/2006-November/019705.html
That was Oleg's response to a post of mine:
Hello,
I'm beginning to think what I'm after is not possible...
I figure I should try to explain exactly what it is I'm after...
Basically I'm trying to mix type hackery with HOAS. More specifically,
here is a data type which I would like to use:
data Exp a where
Lam :: (Exp a -
Hello,
1. Simple documentation of how to install the library (starting from a
vanilla GHC installation on Windows, plus Oracle software, to the
point where I can use the library in my code). All I need is Oracle
access, so other database client libraries can be ignored. I'd rather
not use ODBC,
Hello,
It sure should be possible to use HSPClientside with Text.XHtml,
but off course with exceptions to all Haskell Server Pages (HSP) specific
functions.
Anyway I encourage you to have a look at HSP as well :-)
It's quite nice to be able to use regular XML syntax within the Haskell
code.
Hello,
Are there any Haskell tools to generate javascript? Has anyone made
a combinator library for
javascript?
thanks,
Jeff
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Hello,
There's a Google SoC-project made by a friend of mine for JavaScript
support in Haskell Server Pages:
http://csmisc14.cs.chalmers.se/~bjornson/soc/
It's a combinator library, but i'm not sure it's what you really need
though. :)
This seems to contain just what I was looking for.
Hello,
Good, writeCSV writes out every row immediately after it got it. I
eliminated (++ [nl]) in the hope of reducing the constant factor
slightly. Using difference lists for that is nicer but here you go.
I'm not sure how you'd use difference lists here.
Also, for some reason GHC runs
Hello,
Yet, I'm a bit astonished. I thought that when compiling with -O2,
cosmetic changes should become negligible. Perhaps the strict foldl' has
an effect?
Perhaps... but I doubt that is the main reason. At the moment I have
no idea why there is such a discrepancy between the heap usages...
Hello,
When using addDate in foldM like below, you certainly don't want to
search the cols for the string Date again and again everytime addDate
is called. The index of the Date field is a number determined when
parsing the header. That and only that number has to be plugged in here.
Good
Hello,
The (almost) point-free versions run faster than my fast
imperative version and take up significantly less heap space-- even
the version which reads everything and then writes takes up about 1/3
the heap space as my version.
I get the impression that point-free style is a preventive
Hello,
Try Don Stewart's ByteString library
(http://www.cse.unsw.edu.au/~dons/fps.html). It is much faster than
the standard Haskell IO and now has lazy.
-Jeff
On 9/9/06, Daniel Fischer [EMAIL PROTECTED] wrote:
Hello all,
Now I have an IO-problem, too.
SPOJ problem 41 asks basically to
Hello,
I am running ghc 6.4.1 on mac os X (10.4.5). Can anyone give me some
pointers for getting graphics functionality?
I have tried wxhaskell, but it gives me the error
HelloWorld.hs:4:0:
Failed to load interface for `Graphics.UI.WX':
Bad interface file:
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