Re: [Haskell-cafe] DFAs and self-referential data
Maxime Henrion wrote: I've been playing with some code to work with DFAs, but I'm now faced with an implementation problem. In order to have states that can transition to themselves, it seems I would need self-referential data; otherwise I would need to separate those transitions from the rest and handle them specially in the code. Perhaps an old article http://okmij.org/ftp/misc.html#ccard-transform might be of some help. The article describes not only running a finite automaton (represented as a cyclic graph) on given input but also printing the automaton out and determinizing it: converting NFA to an equivalent DFA. The latter operation converts one cyclic graph to another. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] DFAs and self-referential data
On Tue, Dec 28, 2010 at 3:09 AM, o...@okmij.org wrote: Maxime Henrion wrote: I've been playing with some code to work with DFAs, but I'm now faced with an implementation problem. In order to have states that can transition to themselves, it seems I would need self-referential data; otherwise I would need to separate those transitions from the rest and handle them specially in the code. Perhaps an old article http://okmij.org/ftp/misc.html#ccard-transform might be of some help. The article describes not only running a finite automaton (represented as a cyclic graph) on given input but also printing the automaton out and determinizing it: converting NFA to an equivalent DFA. The latter operation converts one cyclic graph to another. That link was a 404 for me. I think you meant this link: http://okmij.org/ftp/Haskell/misc.html#ccard-transform Thanks! Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Incrementially updating an array
Hi folks!
I have the following problem. As code is most time easier to understand,
let give an example what I try to do in C:
unsigned int i,j;
unsigned int r[100];
for (i = 0; i 100; i++) {
j = makeResult(); //j is known to be smaller than 100.
r[j] = r[j] + 1;
}
(My C is poor, so please don't laugh)
Currently I'm using a Data.Map for this, but as the result is bounded in
this area, an array seems to be more appropreate. I don't want to mess
with mutable arrays, but I can't find anything which does the same like
Data.Map.insertWith for arrays in a reasonable way.
In my example, the input comes from a lazy list and is than folded into
the Map by insertWith (+) j 1 r. Is there any nice, quick way to do this
with Arrays without using mutable ones?
Yours, Robert Clausecker
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Re: [Haskell-cafe] Incrementially updating an array
On Tue, 28 Dec 2010, Robert Clausecker wrote:
Hi folks!
I have the following problem. As code is most time easier to understand,
let give an example what I try to do in C:
unsigned int i,j;
unsigned int r[100];
for (i = 0; i 100; i++) {
j = makeResult(); //j is known to be smaller than 100.
r[j] = r[j] + 1;
}
(My C is poor, so please don't laugh)
Currently I'm using a Data.Map for this, but as the result is bounded in
this area, an array seems to be more appropreate. I don't want to mess
with mutable arrays, but I can't find anything which does the same like
Data.Map.insertWith for arrays in a reasonable way.
Mutable arrays in ST monad sound like a reasonable choice.
In my example, the input comes from a lazy list and is than folded into
the Map by insertWith (+) j 1 r. Is there any nice, quick way to do this
with Arrays without using mutable ones?
You may attach a one to the list elements and then call Array.accum with
(+). The corresponding function in Data.Map is Data.Map.fromListWith with
(+).
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Re: [Haskell-cafe] Incrementially updating an array
On Tue, Dec 28, 2010 at 08:46:24PM +0800, Robert Clausecker wrote:
I have the following problem. As code is most time easier to understand,
let give an example what I try to do in C:
unsigned int i,j;
unsigned int r[100];
for (i = 0; i 100; i++) {
j = makeResult(); //j is known to be smaller than 100.
r[j] = r[j] + 1;
}
(My C is poor, so please don't laugh)
Currently I'm using a Data.Map for this, but as the result is bounded in
this area, an array seems to be more appropreate. I don't want to mess
with mutable arrays, but I can't find anything which does the same like
Data.Map.insertWith for arrays in a reasonable way.
In my example, the input comes from a lazy list and is than folded into
the Map by insertWith (+) j 1 r. Is there any nice, quick way to do this
with Arrays without using mutable ones?
accumArray is designed for situations like this.
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Re: [Haskell-cafe] Template Haskell a Permanent solution?
Hi,
Jonathan Geddes wrote:
For TH use #1, compile-time parsing of arbitrary strings, I think it
would be nice for quasiquote semantics to be modified so that code
like
json :: String - JsonObject
json = ...
data = [ json |
{ name : Jonathan
, favorite language: Haskell
}
|]
causes the function json to be called at compile time with a string
argument of{\name\ : \Jonathan\\n , \favorite language\:
\Haskell\\n }. The whole expression being then replaced with the
result of the function application. What I like about this is that
defining quasiquoters is trivial. They're just functions of the form
String - a. Many such quasiquoters already exist and would be ready
for use! I imagine certain rules would apply, ie a quasiquoter must be
defined prior to use and in a separate module, etc.
First note that this is just quotation, not yet quasiquotation. For
quasiquotation, you would also need to support antiquotation (i.e., the
use of Haskell identifiers or even expressions in the middle of quoted
syntax). And to reach something similar to the current support for
quasiquotation, you would need to support patterns etc., too.
Secondly, I was going to propose to use generic programming to convert
from a parser like (String - JsonObject) to a quasiquoter for Json. But
after half a day of experiments, I figured out that this idea is already
developed in
Geoffrey B. Mainland.
Why It's Nice to be Quoted: Quasiquoting for Haskell.
Haskell Workshop 2007
Available at:
http://www.eecs.harvard.edu/~mainland/publications/mainland07quasiquoting.pdf
In that paper, Geoffrey Mainland explains how a parser can be
generically upgraded to a quoter, reaching an intermediate conclusion on
page 6:
By using generic programming, we can take a parser and create
expression and pattern quasiquoters for the language it parses with
only four lines of code, including type signatures! This holds not
just for our simple object language, but for any object language.
He goes on to explain how to add support for antiquotation [...] with
only slightly more than four lines of code.
The functions dataToExpQ and dataToPatQ from that paper are available in
the TH library in Language.Haskell.TH.Quote. A simple helper function
quasiQuoter :: Data a = (String - Either String a) - QuasiQuoter
quasiQuoter parser = QuasiQuoter
{ quoteExp = either fail (dataToExpQ (const Nothing)) . parse
, quotePat = either fail (dataToPatQ (const Nothing)) . parse
}
should allow you to write your JSON example as follows:
parse :: String - Either String JsonObject
parse = ...
json = quasiQuoter parse
This seems simple enough to me, so it looks as if your use case is
already supported as a library on top of the more general API.
Tillmann
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Re: [Haskell-cafe] Template Haskell a Permanent solution?
On Tue, Dec 28, 2010 at 8:17 AM, Tillmann Rendel ren...@mathematik.uni-marburg.de wrote: This seems simple enough to me, so it looks as if your use case is already supported as a library on top of the more general API. This is exactly what I was looking for, and much simpler than my previous experiences with quasiQuoters. In the original post I said, It may very well be that I am simply not experienced enough with TH to fully appreciate and embrace it. More and more I am thinking this is the case. I'll have to give TH a more thorough look. BTW, in addition to the resources already given, can anyone suggest materials for my aforementioned more thorough look? Thanks again for the responses. --Jonathan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Polymorphic function over pairs of maybes.
Hello all: I'd like to right a function that could take a structure with type (random example): (Int, (String, (Int, Int))) and another where each individual value is a Maybe of the corresponding type, for example: (Maybe Int, (Maybe String, (Maybe Int, Maybe Int))) and perform a fromMaybe using the values to produce a new value with the original types. The catch is, I'd like to be able to do that for an n-deep structure with any type, without having to write a separate function for them. I'm not even sure that this is possible, but perhaps someone could explain how it is or isn't? -- Edward Amsden Undergraduate Computer Science Rochester Institute of Technology www.edwardamsden.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell for Gingerbread
Hi folks, I have been looking at developing for my Android phone which is running Gingerbread (Android version 2.3). The important thing about the official development kit is this: The new native development kit (C/C++ cross compiler for ARM) is that the you can create android applications from pure C without using the Dalvik/Java virtual machine at all. The thinking behind this was probably for game developers to be able to avoid their VM. So all that might be needed is a Haskell compiler with a C-backend that emits ARM-compatible code and an initially minimal android runtime. Implementing to the new native_activity.h allow for the usual application life-cycle: onStart, onPause, onResume, onStop... Some options I have not had a chance to look into: 1) GHC arm port and -via-C 2) jhc (and lhc) generated C 3) port nhc98 4) port yhc bytecode runtime Does anyone know who else is thinking along any of these lines? Are there 5th or 6th routes to take? Cheers, Chris Kuklewicz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Polymorphic function over pairs of maybes.
Maybe something like this would work for you (requires the TypeFamilies extension). class FromMaybe a where type Maybe' a fromMaybe :: a - Maybe' a - a instance FromMaybe Int where type Maybe' Int = Maybe Int fromMaybe = Data.Maybe.fromMaybe instance FromMaybe String where type Maybe' String = Maybe String fromMaybe = Data.Maybe.fromMaybe instance (FromMaybe a, FromMaybe b) = FromMaybe (a, b) where type Maybe' (a, b) = (Maybe' a, Maybe' b) fromMaybe (x, y) (a, b) = (fromMaybe x a, fromMaybe y b) - Jake McArthur ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ghc +RTS -M and -A behaving strange
Hello. When I run a program compiled with ghc-6.12.3 like this: ... +RTS -A2G -M8G -s I get as an answer: Heap exhausted; Current maximum heap size is 0 bytes (0 MB); use `+RTS -Msize' to increase it. and when I put the options ... +RTS -A2000M -M8000M -s I get Heap exhausted; Current maximum heap size is 4093640704 bytes (3904 MB); use `+RTS -Msize' to increase it. and both numbers look strange. The behaviour of the program is also strange (instead of heap exhausted I'd expect it to do some smore garbage collections, which it does indeed without the -A option) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what is the status of haskell's mail libraries?
I've finally gotten around to doing an update to HaskellNet which provides along with some cleanups integration with mime-mail. There is an example of its usage at: example/smtpMimeMail.hs in http://hackage.haskell.org/package/HaskellNet -Rob On Wed, Oct 27, 2010 at 11:05 AM, Michael Snoyman mich...@snoyman.com wrote: On Wed, Oct 27, 2010 at 10:39 AM, Henk-Jan van Tuyl hjgt...@chello.nl wrote: On Wed, 27 Oct 2010 04:46:07 +0200, Michael Snoyman mich...@snoyman.com wrote: I just release mime-mail[1], which can construct multipart messages. Note, that this will not run on Windows, as it gives command /usr/sbin/sendmail The sendmail feature will not work on Windows (and you're right, I should document that more clearly). However, rendering of email messages is completely cross-platform, and there was some talk of getting either HaskellNet or SMTPClient to work with mime-mail, which would allow direct sending of email via SMTP. Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell for Gingerbread
There was work ongoing for an ARM port of GHC. See here: http://tommd.wordpress.com/2010/01/19/ghc-on-arm/ Also see: http://alpheccar.org/en/posts/show/94 Alpheccar's build uses the work of Stephen Blackheath to cross compile, which originated in the GHC-iPhone project, based on ghc 6.10.2 I believe. They are both based on the unregistered C backend, i.e. using the -fvia-C backend. None of this work has been accepted upstream as of me typing this, as far as I know. Certainly the large majority of Stephen's work is not in GHC (in particular things like the POOLSIZE wrapper, which is a workaround for not being able to generate code at runtime via libffi, because the iPhone doesn't allow it. I don't think Android has the same restrictions, here.) There are some plans underway for adding cross compilation support to the GHC build system, see here: http://hackage.haskell.org/trac/ghc/wiki/CrossCompilation In particular this avoids the need for non-standard and painful build setups like alpheccar went through, or the peculiar dance that e.g. HalVM has to go through to cross compile GHC for Xen. Overwhelmingly, I would say focusing efforts on GHC is the way to go. JHC is fiddly (and still fails badly on some simple programs,) ditto for LHC which is highly experimental and not quite as portable. nhc98 would probably be a good baseline, but the lack of language extensions and support from the community probably means you're not going to get a lot to work with it. yhc seems unmaintained. GHC also generates better code than pretty much anything else, too (except when JHC manages to actually work.) GHC is what everybody uses and knows, so it seems best to focus efforts here. Getting GHC to actually support cross compilation in the build system is IMO probably the biggest thing that needs to be done, before any sort of registered ARM port, or adding support for android to the runtime (if that would even be necessary, I have not looked at the Android Gingerbread NDK notes - it may be possible to just have a library that takes care of interfacing with the NDK.) I say this because I think GHC being cross compilable is ultimately a much greater goal than just a port to work on Android/ARM (even debian has had unregistered arm/armel GHC builds for a while, IIRC) and would make using GHC with more exotic toolchains much, much easier (android included.) Until then, your only hope is porting the unregistered compiler, which can be quite frustrating and delicate (and doesn't always work - see the GHC wiki page on Porting.) Perhaps we should be paging Mr. Simon Marlow in here, since he can probably give a better and more concrete answer. On Tue, Dec 28, 2010 at 1:27 PM, Chris Kuklewicz hask...@list.mightyreason.com wrote: Hi folks, I have been looking at developing for my Android phone which is running Gingerbread (Android version 2.3). The important thing about the official development kit is this: The new native development kit (C/C++ cross compiler for ARM) is that the you can create android applications from pure C without using the Dalvik/Java virtual machine at all. The thinking behind this was probably for game developers to be able to avoid their VM. So all that might be needed is a Haskell compiler with a C-backend that emits ARM-compatible code and an initially minimal android runtime. Implementing to the new native_activity.h allow for the usual application life-cycle: onStart, onPause, onResume, onStop... Some options I have not had a chance to look into: 1) GHC arm port and -via-C 2) jhc (and lhc) generated C 3) port nhc98 4) port yhc bytecode runtime Does anyone know who else is thinking along any of these lines? Are there 5th or 6th routes to take? Cheers, Chris Kuklewicz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Regards, Austin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell for Gingerbread
jhc generated C works on the android/ARM just fine. Android specific libraries arn't available, so you would have to bind to what you want with the FFI. John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Polymorphic function over pairs of maybes.
On 28 December 2010 19:23, Edward Amsden eca7...@cs.rit.edu wrote: Hello all: I'd like to right a function that could take a structure with type (random example): (Int, (String, (Int, Int))) and another where each individual value is a Maybe of the corresponding type, for example: (Maybe Int, (Maybe String, (Maybe Int, Maybe Int))) and perform a fromMaybe using the values to produce a new value with the original types. The catch is, I'd like to be able to do that for an n-deep structure with any type, without having to write a separate function for them. I'm not even sure that this is possible, but perhaps someone could explain how it is or isn't? Maybe this is possible with Strafunski or one of the generics libraries that lean in that direction (SYB, KURE, or Oleg Kiselyov's typecase), though I've never looked at descending into two terms at the same time even if they have the same type shape. http://okmij.org/ftp/Haskell/typecast.html At a meta-level do you have a need for this, or is it just a curiosity? If it is for some real world situation, I suspect there are simpler ways of achieving the functionality you seem to want. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Polymorphic function over pairs of maybes.
Although I don't understand it myself Oleg's deepest functor [1] seems to be what you're looking for. -deech [1] http://okmij.org/ftp/Haskell/deepest-functor.lhs On Tue, Dec 28, 2010 at 1:23 PM, Edward Amsden eca7...@cs.rit.edu wrote: Hello all: I'd like to right a function that could take a structure with type (random example): (Int, (String, (Int, Int))) and another where each individual value is a Maybe of the corresponding type, for example: (Maybe Int, (Maybe String, (Maybe Int, Maybe Int))) and perform a fromMaybe using the values to produce a new value with the original types. The catch is, I'd like to be able to do that for an n-deep structure with any type, without having to write a separate function for them. I'm not even sure that this is possible, but perhaps someone could explain how it is or isn't? -- Edward Amsden Undergraduate Computer Science Rochester Institute of Technology www.edwardamsden.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Polymorphic function over pairs of maybes.
On Tue, Dec 28, 2010 at 21:23, Edward Amsden eca7...@cs.rit.edu wrote: (Int, (String, (Int, Int))) and another where each individual value is a Maybe of the corresponding type, for example: (Maybe Int, (Maybe String, (Maybe Int, Maybe Int))) This example demonstrates exactly why you might want to avoid doing this... if you apply Maybe as deeply inside type constructors as possible, you actually get (Maybe Int, ([Maybe Char], (Maybe Int, Maybe Int))) and in general you may not know or care whether a type is atomic or not. There may be a way which works if you specify the target type as well. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Polymorphic function over pairs of maybes.
Aditya: Not quite, because I'm actually looking to extract values from a functor (Maybe) with a default. Stephen: Thanks, I'll take a look at those. I do have a need for it. I'm writing a very similar library to Yampa. (I would be patching Yampa, but the code is a mess, so I decided to try starting from scratch.) Basically, I have a signal processing loop, where values are passed updated with a Maybe, representing whether there is or is not a change to the value. I could use a single Maybe around the whole thing, but that would require then re-updating a potentially large structure entirely. I want to be able to build a combinator that can combine two signal-fetching actions into a larger one: IO (Maybe a) - IO (...) - IO (Maybe a, (...)) and then an action that could, given the previous value: (a, (...)) update any places in this chain of pairs where the Maybe is not Nothing. Jake: I'd prefer to not have to define class instances for the types. It would get tedious and awkward quickly. (See above for a description of what I'm looking for.) -- Edward Amsden Undergraduate Computer Science Rochester Institute of Technology www.edwardamsden.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] multi type addition
We were trying to make an addition function that, unlike the library one, could add numbers of different types from the typeclass 'Num.' We originally ran into a problem when trying to add (5 :: Integer) + 4.8, and were trying to define a new function that would be able to get that: (+') :: (Num a, Num b) = a - b - Float x +' b = d + e where d :: Float d = x e :: Float e = b This gave us the error: Couldn't match expected type `Float' against inferred type `b' `b' is a rigid type variable bound by the type signature for `pl' at test.hs:9:18 In the expression: b In the definition of `e': e = b In the definition of `pl': pl x b = d + e where d :: Float d = x e :: Float e = b Failed, modules loaded: none. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Polymorphic function over pairs of maybes.
Basically, I have a signal processing loop, where values are passed updated with a Maybe, representing whether there is or is not a change to the value. I could use a single Maybe around the whole thing, but that would require then re-updating a potentially large structure entirely. I want to be able to build a combinator that can combine two signal-fetching actions into a larger one: IO (Maybe a) - IO (...) - IO (Maybe a, (...)) and then an action that could, given the previous value: (a, (...)) update any places in this chain of pairs where the Maybe is not Nothing. Sounds like you want a generic diff: http://hackage.haskell.org/package/gdiff-1.0 Cheers, Sterl ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Polymorphic function over pairs of maybes.
On 28 December 2010 21:44, Edward Amsden eca7...@cs.rit.edu wrote: [SNIP] I'm writing a very similar library to Yampa. (I would be patching Yampa, but the code is a mess, so I decided to try starting from scratch.) Basically, I have a signal processing loop, where values are passed updated with a Maybe, representing whether there is or is not a change to the value. I could use a single Maybe around the whole thing, but that would require then re-updating a potentially large structure entirely. I want to be able to build a combinator that can combine two signal-fetching actions into a larger one: Hi Edward That's a tough proposition - phrased in a different way, you want syntax (i.e algebraic data types) with holes. Functors (List, Data.Sequence, ...) and Bifunctors (pairs and Either, ...) have obvious holes, and working with holey things is possible[*] but its probably way too far out for signal processing where you have efficiency concerns. Is it common for Reactive libraries like Yampa to operate on a large World datatype - rather than streams of signals of some atomic unit like Double? If it were me, I'd want to answer this question first before attempting to represent it. [*] See Conor McBride's Clowns and Jokers for instance: http://personal.cis.strath.ac.uk/~conor/Dissect.pdf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] multi type addition
The problem here is that unfortunately the Haskell type system cannot do coercion. There is however a toRational method Real typeclass that converts instances of Num and Ord to Rational data type and a fromRational method that converts back. So your code could be: myplus :: (Real a, Real b) = a - b - Float a `myplus` b = fromRational(toRational a + toRational b) (1 :: Integer) `myplus` (2::Integer) 3.0 (1.5 :: Float) `myplus` (2::Integer) 3.5 -deech [1] http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.html#t:Real [2] http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.html#t:Rational On Tue, Dec 28, 2010 at 3:45 PM, william murphy will.t.mur...@gmail.com wrote: We were trying to make an addition function that, unlike the library one, could add numbers of different types from the typeclass 'Num.' We originally ran into a problem when trying to add (5 :: Integer) + 4.8, and were trying to define a new function that would be able to get that: (+') :: (Num a, Num b) = a - b - Float x +' b = d + e where d :: Float d = x e :: Float e = b This gave us the error: Couldn't match expected type `Float' against inferred type `b' `b' is a rigid type variable bound by the type signature for `pl' at test.hs:9:18 In the expression: b In the definition of `e': e = b In the definition of `pl': pl x b = d + e where d :: Float d = x e :: Float e = b Failed, modules loaded: none. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] What's the motivation for η rul es?
TIA, David -- David Sankel Sankel Software www.sankelsoftware.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What's the motivation for η rul es?
Eta conversion corresponds to extensionality; i.e. there is nothing more to a function than what it does to its argument. Suppose f x = g x for all x. Then using eta conversion: f = (\x. f x) = (\x. g x) = g Without eta this is not possible to prove. It would be possible for two functions to be distinct (well, not provably so) even if they do the same thing to every argument -- say if they had different performance characteristics. Eta is a controversial rule of lambda calculus -- sometimes it is omitted, for example, Coq does not use it. It tends to make things more difficult for the compiler -- I think Conor McBride is the local expert on that subject. On Tue, Dec 28, 2010 at 4:12 PM, David Sankel cam...@gmail.com wrote: TIA, David -- David Sankel Sankel Software www.sankelsoftware.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What's the motivation for η rules?
One way to look at it is that β rules are the application of an eliminator (e.g. function application) to its corresponding constructor (the lambda expression), whereas η rules correspond to the application of a constructor to its corresponding eliminator. E.g. λ y . (x y)= x if x then True else False = x (π₁ x, π₂ x) = x IOW there's no need for a motivation: those rules just appear naturally. Stefan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what is the status of haskell's mail libraries?
This looks very good, thank you! One comment: do you think it would be possible to add a function for sending a mime-mail Mail datatype directly? I see that you provide a wrapper around simpleMail in your sendMimeMail function, but that won't always be sufficient. Michael On Tue, Dec 28, 2010 at 9:46 PM, Robert Wills wrwi...@gmail.com wrote: I've finally gotten around to doing an update to HaskellNet which provides along with some cleanups integration with mime-mail. There is an example of its usage at: example/smtpMimeMail.hs in http://hackage.haskell.org/package/HaskellNet -Rob On Wed, Oct 27, 2010 at 11:05 AM, Michael Snoyman mich...@snoyman.com wrote: On Wed, Oct 27, 2010 at 10:39 AM, Henk-Jan van Tuyl hjgt...@chello.nl wrote: On Wed, 27 Oct 2010 04:46:07 +0200, Michael Snoyman mich...@snoyman.com wrote: I just release mime-mail[1], which can construct multipart messages. Note, that this will not run on Windows, as it gives command /usr/sbin/sendmail The sendmail feature will not work on Windows (and you're right, I should document that more clearly). However, rendering of email messages is completely cross-platform, and there was some talk of getting either HaskellNet or SMTPClient to work with mime-mail, which would allow direct sending of email via SMTP. Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Having trouble with ftphs module
Hi all: I'm new to Haskell, and I ran into this problem recently while I am using ftphs module downloaded from hackage. Prelude :m Network.FTP.Client Prelude Network.FTP.Client h - easyConnectFTP xxx.xxx.xxx.xxx *** Exception: FTP: (unknown) (line 2, column 1): unexpected \r expecting \r\n or Code 220 I am not the administrator of this FTP server. Hence all I've been told is that it is a Microsoft FTP Server. I want to know 1. if this should be regarded as a bug of ftphs or not? 2. is there any other workaround other than the one below? Possible workaround: Implement another BAT script to do the FTP work and use system() to invoke it. Thanks in advance. -- Best regards, -Tian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
