[Haskell-cafe] How to input Unicode string in Haskell program?
Imagine we have this simple program: module Main(main) where main = do x - getLine putStrLn x Now I want to run it somehow, enter résumé 履歴書 резюме and see this string printed back as résumé 履歴書 резюме. Now, the first problem is that my computer runs Windows, which means that I can't use ghci :main or result of ghc main.hs to enter such an outrageous string — Windows console is locked to one specific local code page, and no codepage contains Latin-1, Cyrillic and Kanji symbols at the same time. But there is also WinGHCi. So I do :main, copy-paste this string into the window (It works! Because Windows has Unicode for 20 years now), but the output is all messed up. In a rather curious way, actually: the input string is converted to UTF-8 byte string, and its bytes are treated as being characters from my local code page. So, it appears that I have no way to enter Unicode strings into my Haskell programs by hands, I should read them from files. That's sad, and I refuse to think I am the first one with such a problem, so I assume there is a solution/workaround. Now would someone please tell me this solution? Except from Just stick to 127 letters of ASCII, of course. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parser left recursion
As mentioned before, the way to handle this specific problem is to use either
the pChainl or pChainr parser combinators, as e.g. found on:
http://hackage.haskell.org/packages/archive/uu-parsinglib/2.7.4.1/doc/html/Text-ParserCombinators-UU-Derived.html
and many similar libraries. So one can write:
pExpr = pChainl ( (+) $ pSym ' ')) pFactor
pFactor = iI '(' pExpr ')' Ii | pInteger | pIdentifier
What is even nicer is that one can easily extend this to deal with many
different operators:
pExpr = foldr nextop [((+),'+'), ((*), '*'))] pGactor
where nextop (sem,sym) = pChainl sem $ pSym sym))
It is obvious how to extend this further into operators with the same priority
or being right associative. See furthermore:
@inproceedings{Fokker95:0,
title = {Functional Parsers},
author = {Jeroen Fokker},
year = {1995},
tags = {parsing},
researchr = {http://dutieq.st.ewi.tudelft.nl/publication/Fokker95%3A0},
cites = {0},
citedby = {0},
pages = {1-23},
booktitle = {Advanced Functional Programming, First International Spring
School on Advanced Functional Programming Techniques, Båstad, Sweden, May
24-30, 1995, Tutorial Text},
editor = {Johan Jeuring and Erik Meijer},
volume = {925},
series = {Lecture Notes in Computer Science},
publisher = {Springer},
isbn = {3-540-59451-5},
}
Most left recursion stems from the fact that conventional CFG notation is
sufficient, but unfortunately not ideally suited, to express oft occurring
patterns. This is where parser combinators come in: they allow one to express
what one wants to say instead of having to encode it using recursion, etc.
If you have a really nasty grammar where left recursion removal by hand would
ruin your grammar, you may use a transform like the LeftCornerTransform as used
e.g. in the ChristmasTree package, which removes the problem of exponential
time behaviour of reading Haskell data types with infix operators. See:
http://hackage.haskell.org/package/ChristmasTree-0.2, and which has been
described in:
@article{DBLP
:journals/entcs/BaarsSV10,
author= {Arthur I. Baars and
S. Doaitse Swierstra and
Marcos Viera},
title = {Typed Transformations of Typed Grammars: The Left Corner
Transform},
journal = {Electr. Notes Theor. Comput. Sci.},
volume= {253},
number= {7},
year = {2010},
pages = {51-64},
ee= {http://dx.doi.org/10.1016/j.entcs.2010.08.031},
bibsource = {DBLP, http://dblp.uni-trier.de}
}
Doaitse
On Feb 20, 2013, at 8:13 , Martin Drautzburg martin.drautzb...@web.de wrote:
Hello all,
this was previously asked on haskell-beginners, but only partially answered.
As an exercise I am writing a parser roughly following the expamples in
Graham
Hutton's book. The language contains things like:
data Exp = Lit Int -- literal integer
| Plus Exp Exp
My naive parser enters an infinite recursion, when I try to parse 1+2. I do
understand why:
hmm, this expression could be a plus, but then it must start with an
expression, lets check.
and it tries to parse expression again and again considers Plus.
Twan van Laarhoven told me that:
Left-recursion is always a problem for recursive-descend parsers.
and suggested to do something like:
parseExp = do
lit - parseLit
pluses - many (parsePlusToken * parseLit)
return (combinePlusesWithLit lit pluses)
combinePlusesWithLit = foldr Plus -- or foldl
This indeed does the trick, but only when the first token is a Lit (literal
integer).
I then added the possibility to optionally put things in parentheses. But
then
I cannot parse (1+2)+3. The original code fails, because (1+2) is not a
Lit and when I allow an expression as the first argument to + I get
infinite
recursion again.
I am generally confused, that saying a plus expression is an integer
followed
by many plus somethings is not what the language says. So this requires a
lot of paying attention to get right. I'd much rather say a plus
expression
is two expressions with a '+' in between.
I do know for sure, that it is possible to parse (1+2)+3 (ghci does it just
fine). But I seem to be missing a trick.
Can anyone shed some light on this?
--
Martin
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[Haskell-cafe] question about: --hyperlink-source
I ran into the problem that for the packages which I install using cabal install The generated html does not contain links to the sources. This issue was raised before in: http://stackoverflow.com/questions/1587635/haddock-for-cabal-installed-modules I have been looking into the documentation available, but could not find a way to set this e.g. as a default in some .haddock file. Am I overlooking something? Doaitse ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: data-fix-cse -- Common subexpression elimination for EDSLs
This should be possible using higher-order terms, as in http://hackage.haskell.org/packages/archive/compdata/latest/doc/html/Data-Comp-Multi-Term.html The only complication I see is that the Dag nodes would get heterogeneous types requiring existential quantification with a `Typeable` constraint. A better representation might be typed ASGs [1] Syntactic has typed ASTs and it has a module that does something similar to data-fix-cse (uses a combination of stable names and hashing), but it needs some fixing up. / Emil [1]: http://dl.acm.org/citation.cfm?id=2426909 2013-02-20 01:58, Conal Elliott skrev: Do you think the approach can be extended for non-regular (nested) algebraic types (where the recursive data type is sometimes at a different type instance)? For instance, it's very handy to use GADTs to capture embedded language types in host language (Haskell) types, which leads to non-regularity. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] question about: --hyperlink-source
On 21 February 2013 21:18, Doaitse Swierstra doai...@swierstra.net wrote: I ran into the problem that for the packages which I install using cabal install The generated html does not contain links to the sources. This issue was raised before in: http://stackoverflow.com/questions/1587635/haddock-for-cabal-installed-modules I have been looking into the documentation available, but could not find a way to set this e.g. as a default in some .haddock file. Am I overlooking something? I don't think this is currently possible: https://github.com/haskell/cabal/issues/510 Doaitse ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com http://IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to input Unicode string in Haskell program?
Have you tried running ghci inside Emacs? Отправлено с iPhone 21.02.2013, в 13:58, Semyon Kholodnov joker...@gmail.com написал(а): Imagine we have this simple program: module Main(main) where main = do x - getLine putStrLn x Now I want to run it somehow, enter résumé 履歴書 резюме and see this string printed back as résumé 履歴書 резюме. Now, the first problem is that my computer runs Windows, which means that I can't use ghci :main or result of ghc main.hs to enter such an outrageous string — Windows console is locked to one specific local code page, and no codepage contains Latin-1, Cyrillic and Kanji symbols at the same time. But there is also WinGHCi. So I do :main, copy-paste this string into the window (It works! Because Windows has Unicode for 20 years now), but the output is all messed up. In a rather curious way, actually: the input string is converted to UTF-8 byte string, and its bytes are treated as being characters from my local code page. So, it appears that I have no way to enter Unicode strings into my Haskell programs by hands, I should read them from files. That's sad, and I refuse to think I am the first one with such a problem, so I assume there is a solution/workaround. Now would someone please tell me this solution? Except from Just stick to 127 letters of ASCII, of course. ___ 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] PhD Studentship in Nottingham
Dear all, The School of Computer Science at the University of Nottingham is currently advertising a PhD position on applying functional programming techniques to optimisation problems: http://www.cs.nott.ac.uk/~ajp/PhD-opportunities.htm This would be a great position for someone who is interested in applying FP ideas to real-world problems. The closing date for applications is 28th February 2013. If you have any queries about the position, please contact Andrew Parkes andrew.par...@nottingham.ac.uk. Best wishes, Graham -- Prof Graham Hutton Functional Programming Lab School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~gmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to input Unicode string in Haskell program?
You can also set the locale encoding for a handle (e.g. System.IO.stdin) from code using `System.IO.hSetEncoding` [0]. Erik [0] http://hackage.haskell.org/packages/archive/base/latest/doc/html/System-IO.html#v:hSetEncoding On Thu, Feb 21, 2013 at 12:07 PM, Alexander V Vershilov alexander.vershi...@gmail.com wrote: The problem is that Prelude.getLine uses current locale to load characters: for example if you have utf8 locale, then everything works out of the box: $ runhaskell 1.hs résumé 履歴書 резюме résumé 履歴書 резюме But if you change locale you'll have error: LANG=C runhaskell 1.hs résumé 履歴書 резюме 1.hs: stdin: hGetLine: invalid argument (invalid byte sequence) To force haskell use UTF8 you can load string as byte sequence and convert it to UTF-8 charecters for example by import qualified Data.ByteString as S import qualified Data.Text.Encoding as T main = do x - fmap T.decodeUtf8 S.getLine now code will work even with different locale, and you'll load UTF8 from shell independenty of user input's there -- Alexander On 21 February 2013 13:58, Semyon Kholodnov joker...@gmail.com wrote: Imagine we have this simple program: module Main(main) where main = do x - getLine putStrLn x Now I want to run it somehow, enter résumé 履歴書 резюме and see this string printed back as résumé 履歴書 резюме. Now, the first problem is that my computer runs Windows, which means that I can't use ghci :main or result of ghc main.hs to enter such an outrageous string — Windows console is locked to one specific local code page, and no codepage contains Latin-1, Cyrillic and Kanji symbols at the same time. But there is also WinGHCi. So I do :main, copy-paste this string into the window (It works! Because Windows has Unicode for 20 years now), but the output is all messed up. In a rather curious way, actually: the input string is converted to UTF-8 byte string, and its bytes are treated as being characters from my local code page. So, it appears that I have no way to enter Unicode strings into my Haskell programs by hands, I should read them from files. That's sad, and I refuse to think I am the first one with such a problem, so I assume there is a solution/workaround. Now would someone please tell me this solution? Except from Just stick to 127 letters of ASCII, of course. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Alexander ___ 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] Fwd: How to input Unicode string in Haskell program?
-- Forwarded message -- From: Semyon Kholodnov joker...@gmail.com Date: Thu, 21 Feb 2013 16:26:58 +0400 Subject: Re: [Haskell-cafe] How to input Unicode string in Haskell program? To: Alexander V Vershilov alexander.vershi...@gmail.com I know that this problem doesn't exist on Linux. But I work on Windows. And I use WinGHCi primarily, because it has RTF component in it which shows Unicode. But it turns out WinGHCi merely sends commands and receives results to/from ghci.exe. And it does it in a weird way: it sets ghci's console code pages to current system codepages (ACP), reads results from ghci as ACP, but sends commands to it as UTF8. Which got interpreted as ACP. Now, however, I have a fix for WinGHCi: in StartGHCI.c one should replace SetConsoleOutputCP(GetACP()); SetConsoleCP(GetACP()); with SetConsoleOutputCP(CP_UTF8); SetConsoleCP(CP_UTF8); and in Utf8.c, in UnicodeToLocalCodePage() body, WideCharToMultiByte( CP_ACP has to be replaced with WideCharToMultiByte( CP_UTF8, and in LocalCodePageToUnicode() body, MultiByteToWideChar( CP_ACP has to be replaced with MultiByteToWideChar( CP_UTF8. After recompiling, everything works great: Prelude x - getLine résumé 履歴書 резюме Prelude putStrLn x résumé 履歴書 резюме Prelude Is there any way to ask for this fix to be included in WinGHCi and Haskell Platform? 2013/2/21, Alexander V Vershilov alexander.vershi...@gmail.com: The problem is that Prelude.getLine uses current locale to load characters: for example if you have utf8 locale, then everything works out of the box: $ runhaskell 1.hs résumé 履歴書 резюме résumé 履歴書 резюме But if you change locale you'll have error: LANG=C runhaskell 1.hs résumé 履歴書 резюме 1.hs: stdin: hGetLine: invalid argument (invalid byte sequence) To force haskell use UTF8 you can load string as byte sequence and convert it to UTF-8 charecters for example by import qualified Data.ByteString as S import qualified Data.Text.Encoding as T main = do x - fmap T.decodeUtf8 S.getLine now code will work even with different locale, and you'll load UTF8 from shell independenty of user input's there -- Alexander On 21 February 2013 13:58, Semyon Kholodnov joker...@gmail.com wrote: Imagine we have this simple program: module Main(main) where main = do x - getLine putStrLn x Now I want to run it somehow, enter résumé 履歴書 резюме and see this string printed back as résumé 履歴書 резюме. Now, the first problem is that my computer runs Windows, which means that I can't use ghci :main or result of ghc main.hs to enter such an outrageous string — Windows console is locked to one specific local code page, and no codepage contains Latin-1, Cyrillic and Kanji symbols at the same time. But there is also WinGHCi. So I do :main, copy-paste this string into the window (It works! Because Windows has Unicode for 20 years now), but the output is all messed up. In a rather curious way, actually: the input string is converted to UTF-8 byte string, and its bytes are treated as being characters from my local code page. So, it appears that I have no way to enter Unicode strings into my Haskell programs by hands, I should read them from files. That's sad, and I refuse to think I am the first one with such a problem, so I assume there is a solution/workaround. Now would someone please tell me this solution? Except from Just stick to 127 letters of ASCII, of course. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Alexander ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unused definitions across modules in a package
On Wed, Feb 20, 2013 at 9:20 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: My (getting-long-in-the-tooth-and-could-do-with-a-rewrite) SourceGraph package does identify these definitions. What a coincidence, then! I was trying to use SourceGraph for other reasons but it didn't work for my codebase. I haven't investigated with it couldn't parse the files, though, and I use many extensions. Nice to know that it supports this feature =). Cheers, -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: mcpi-0.0.0.2 (The MineCraft-Pi API in Haskell)
I have released versions 0.0.0.1 and 0.0.0.2 (the latter being documentation improvements but it hasn't yet been built) of mcpi: http://hackage.haskell.org/package/mcpi https://github.com/DougBurke/hmcpi It is a very simple, and very incomplete, interface to MineCraft: Pi edition http://pi.minecraft.net/ Now I just need to find out how to get ghc 7.4.2 on my Raspberry Pi (oops, I mean the Raspberry Pi I told my wife I bought as a Christmas gift for the kids) so that I can use this from ghci. Any comments and improvements are more than welcome, Doug ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] generalized, tail-recursive left fold that can
Thanks, I see now where my mistake was.
Laziness (or call by name) is needed to make the step from
(\e a z - a (f z e))
(head l)
(foldr (\e a z - a (f z e)) id (tail l) z)
(f z (head l))
to
\z - foldr (\e a z - a (f z e)) id (tail l) (f z (head l))
without evaluating foldr further.
Roman
* o...@okmij.org o...@okmij.org [2013-02-20 04:23:34-]
That said, to express foldl via foldr, we need a higher-order
fold. There are various problems with higher-order folds, related to
the cost of building closures. The problems are especially severe
in strict languages or strict contexts. Indeed,
foldl_via_foldr f z l = foldr (\e a z - a (f z e)) id l z
first constructs the closure and then applies it to z. The closure has
the same structure as the list -- it is isomorphic to the
list. However, the closure representation of a list takes typically
quite more space than the list. So, in strict languages, expressing
foldl via foldr is a really bad idea. It won't work for big lists.
If we unroll foldr once (assuming l is not empty), we'll get
\z - foldr (\e a z - a (f z e)) id (tail l) (f z (head l))
which is a (shallow) closure. In order to observe what you describe (a
closure isomorphic to the list) we'd need a language which does
reductions inside closures.
I should've elaborated this point.
Let us consider monadic versions of foldr and foldl. First, monads,
sort of emulate strict contexts, making it easier to see when
closures are constructed. Second, we can easily add tracing.
import Control.Monad.Trans
-- The following is just the ordinary foldr, with a specialized
-- type for the seed: m z
foldrM :: Monad m =
(a - m z - m z) - m z - [a] - m z
-- The code below is identical to that of foldr
foldrM f z [] = z
foldrM f z (h:t) = f h (foldrM f z t)
-- foldlM is identical Control.Monad.foldM
-- Its code is shown below for reference.
foldlM, foldlM' :: Monad m =
(z - a - m z) - z - [a] - m z
foldlM f z []= return z
foldlM f z (h:t) = f z h = \z' - foldlM f z' t
t1 = foldlM (\z a - putStrLn (foldlM: ++ show a)
return (a:z)) [] [1,2,3]
{-
foldlM: 1
foldlM: 2
foldlM: 3
[3,2,1]
-}
-- foldlM' is foldlM expressed via foldrM
foldlM' f z l =
foldrM (\e am - am = \k - return $ \z - f z e = k)
(return return) l = \f - f z
-- foldrM'' is foldlM' with trace printing
foldlM'' :: (MonadIO m, Show a) =
(z - a - m z) - z - [a] - m z
foldlM'' f z l =
foldrM (\e am - liftIO (putStrLn $ foldR: ++ show e)
am = \k - return $ \z - f z e = k)
(return return) l = \f - f z
t2 = foldlM'' (\z a - putStrLn (foldlM: ++ show a)
return (a:z)) [] [1,2,3]
{-
foldR: 1
foldR: 2
foldR: 3
foldlM: 1
foldlM: 2
foldlM: 3
[3,2,1]
-}
As we can see from the trace printing, first the whole list is
traversed by foldR and the closure is constructed. Only after foldr
has finished, the closure is applied to z ([] in our case), and
foldl's function f gets a chance to work. The list is effectively
traversed twice, which means the `copy' of the list has to be
allocated -- that is, the closure that incorporates the calls to
f e1, f e2, etc.
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[Haskell-cafe] websockets client
Are there any good websockets client libraries for haskell. I've been searching for one but can only come up with server implementations. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] websockets client
Hi, websockets package has basic support for client-side applications: http://hackage.haskell.org/packages/archive/websockets/0.7.2.1/doc/html/Network-WebSockets.html#g:12 AFAIK it is the only available option right now (except implementing it yourself.) Thanks, Yuras On Thu, 2013-02-21 at 16:09 -0500, Stephen Olsen wrote: Are there any good websockets client libraries for haskell. I've been searching for one but can only come up with server implementations. ___ 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] websockets client
Yes, Jasper's websockets has a client in recent versions that works really nicely since server and client have the same APIs. The example was a little hidden: https://github.com/jaspervdj/websockets/blob/master/example/client.hs On Thu, Feb 21, 2013 at 10:09 PM, Stephen Olsen steve.ol...@gmail.comwrote: Are there any good websockets client libraries for haskell. I've been searching for one but can only come up with server implementations. ___ 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] GHC panicking when using -fext-core -O2
Hi Cafe, when I try to create core files with the above options, ghc panics with this message: ghc: panic! (the 'impossible' happened) (GHC version 7.6.2 for x86_64-unknown-linux): make_exp (App _ (Coercion _)) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug I tried this with 7.4.1 and with 7.6.2. Does anyone have an idea why this could happen, without looking at the code I am trying to compile? Thanks for any hint, Christian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
