Re: [Haskell-cafe] Qualified import syntax badly designed (?)
I think a better design for namespacing might be: import Data.Map as M implicit (Map) import Data.Map as M explicit (lookup) Why 'implicit' and 'explicit'? Do you mean something like 'include' and 'exclude'? To me at least, implicit and explicit make more sense. I don't want to exclude importing lookup, I want to make it so I have to explicitly tag lookup as being M.lookup. Similarly, I don't want to include Map (as opposed to all the other things I'm getting from Data.Map), I just want to make it so that when I say Map, I implicitly mean M.Map. Personally I'd extend this syntax (something Neil may have had in mind), so that import Data.Map as M (lookup, union) implicit (Map) gives me M.lookup, M.union and Map while import Data.Map as M hiding (union) explicit (lookup) gives me everything in Data.Map with no qualification except for union and lookup, plus it gives me M.lookup. Bob ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] use of the GHC universal quantifier
Try {-# LANGUAGE RankNTypes #-}?
forall does denote a universal quantifier, but because the 'implies'
of the function arrow, in logic, includes negation, you can use it to
emulate existential quantifiers.
data Existential = forall a. Ex a
The type of the constructor Ex:
Ex :: forall a. a - Existential
Pattern matching on Ex brings a back into scope (with no information
about it, so this type isn't that useful on its own):
use (Ex x) = 0 -- can't recover any useful information about x
sample = Ex sample
However, you can use existential types to encode additional
information about the included data; for example:
-- Ex2 :: forall a. Show a = a - Exist2
data Exist2 = forall a. Show a = Ex2 a
Now, pattern matching on Ex2 brings the Show instance into scope as well:
sample2 = Ex2 sample2
use2 (Ex2 x) = show x
You can also use higher rank polymorphism to encode existential types:
-- Ex3 :: (forall a. (forall b. Show b = b - a) - a) - Exist3
-- note the rank-3 type on Ex3!
newtype Exist3 = Ex3 (forall a. (forall b. Show b = b - a) - a)
sample3 = Ex3 (\k - k sample3)
use3 (Ex3 f) = f (\x - show x)
-- ryan
2008/7/8 Galchin, Vasili [EMAIL PROTECTED]:
Hello,
It seems to me by its name that forall denotes a logical universal
quantifier. In any case, hsql-1.7/Database/HSQL/Types.hs uses forall at
line #134. I got a nasty build so I added {-# LANGUAGE
ExistentialQuantification #-} at the top of the module. Now I get the
following a coupleof lines up:
Database/HSQL/Types.hs:131:5:
Illegal polymorphic or qualified type: forall a.
Int
- FieldDef
- FieldDef
- CString
- Int
- IO a
- IO a
In the definition of data constructor `Statement'
In the data type declaration for `Statement'
If seems that GHC doesn't like a. Why?
Kind regards, Vasili
___
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] FPGA / Lava and haskell
You're going to design something like that with an FPGA in it? :) The FPGA is only used for developement. If everything works fine I'd like to put it on the market. My hope is to get one low cost chip doing everything this way. Would you suggest using other tools? I'm still a total noob in this area For a simple enough design, it can be useful to write specs in Haskell and then translate them to HDL by hand. I believe someone on this list had a particularly successful experience doing that :). Thanks for this note. Marc Weber ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Interesting feature
David Overton wrote: Also, see my recent attempts at (constraint) logic programming in Haskell: http://overtond.blogspot.com/2008/07/pre.html http://overtond.blogspot.com/2008/07/haskell-sudoku-solver-using-finite.html See the Sudoku page on the wiki: http://www.haskell.org/haskellwiki/Sudoku Please add your solver there. Regards, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
Hi declaration with a regular syntax. For example: import Data.Map as Map unqualified (Map, (\\)) qualified (lookup, map, null) hiding (filter) I think I prefer this to my proposal, plus its closer to the current syntax. I think its also nearly equal to what Tom Davie came up with, given some keyword renaming. If we dropped the unqualified keyword, and just required unqualified things to come directly after, we get the full benefits of not introducing any keywords. * A special case can be made when all three clauses are dropped so that, if there's no 'as'-clause then everything is imported unqualified, otherwise everything is imported qualified. That's not the current semantics. Currently 'as' means everything is imported unqualified and also qualified. Why 'implicit' and 'explicit'? Do you mean something like 'include' and 'exclude'? I want to refer to these things explicitly (with a module name), I want to refer to these things implicitly (without a module name). I have no particular attachment to the keywords - think of it as a discussion starter rather than a suggestion. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
Neil Mitchell wrote: Hi declaration with a regular syntax. For example: import Data.Map as Map unqualified (Map, (\\)) qualified (lookup, map, null) hiding (filter) I think I prefer this to my proposal, plus its closer to the current syntax. I think its also nearly equal to what Tom Davie came up with, given some keyword renaming. If we dropped the unqualified keyword, and just required unqualified things to come directly after, we get the full benefits of not introducing any keywords. Just to say that I also like this design. A minor point would be; do we really need the parentheses and commas? or could we not just use indentation (I think this about module imports in general). Also I wouldn't mind 'as' for the names which are imported which would be a bit of a work around for the debate as to whether I should design my modules for qualified import or not. Suppose I make a 'NewList' module and use the default names then someone could do: import Data.NewList unqualified map as nlMap find as nlFind lookup as nlLookup or vice-versa. regards allan -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
Hi
Just to say that I also like this design. A minor point would be; do we
really need the parentheses and commas? or could we not just use
indentation (I think this about module imports in general).
Yes, then you could just uses {a;b} to get the list which is actually
a newline list. I think this would be even better for module
declarations.
For example, in the module I'm currently working on:
module Hoogle.DataBase.TypeSearch.Graph(
Graph, newGraph,
GraphResult(..), ArgPos, Binding,
graphSearch
) where
I dislike the fact that ,'s come after every line but the last - it
lacks consistency, and often requires 1 more line of diff when adding
somethign (add comma to previous line, and add the line). I would
rather write:
module Hoogle.DataBase.TypeSearch.Graph{
Graph; newGraph
GraphResult(..); ArgPos; Binding
graphSearch
} where
However, I think the new syntax for modules, and the new type of
declarations for modules, are separate issues.
Also I wouldn't mind 'as' for the names which are imported which would
be a bit of a work around for the debate as to whether I should design
my modules for qualified import or not. Suppose I make a 'NewList'
module and use the default names then someone could do:
import Data.NewList
unqualified map as nlMap
find as nlFind
lookup as nlLookup
I believe old versions of Haskell had this, and it was considered too
confusing. Consider:
import Prelude unqualified (+) as (-)
Also people reading the code will find it easier to know N =
Data.NewList (one mapping), than three mappings as you have.
Thanks
Neil
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
Neil Mitchell wrote: Hi Just to say that I also like this design. A minor point would be; do we really need the parentheses and commas? or could we not just use indentation (I think this about module imports in general). [snip general agreement] However, I think the new syntax for modules, and the new type of declarations for modules, are separate issues. Sure! Also I wouldn't mind 'as' for the names which are imported which would be a bit of a work around for the debate as to whether I should design my modules for qualified import or not. Suppose I make a 'NewList' module and use the default names then someone could do: import Data.NewList unqualified map as nlMap find as nlFind lookup as nlLookup I believe old versions of Haskell had this, and it was considered too confusing. Consider: import Prelude unqualified (+) as (-) Also people reading the code will find it easier to know N = Data.NewList (one mapping), than three mappings as you have. Yes I generally agree there, I don't think 'as' for imported names is particularly important and if it's been tried before and found to be confusing well then that pretty much settles it for me. If I were particularly for it then I'd point out that: import Prelude unqualified (+) as (-) would only be written by someone with limited common sense or someone trying to break things (but I'm sure you could come up with a more realistic example). More importantly for me is the consistency you mentioned, for me it seems inconsistent that you can remap a module name but not an imported identifier. That said, your point about knowing one or three mappings is somewhat compelling and I'm now somewhat less in favour of 'as' for imported names. regards allan -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
On Wed, 9 Jul 2008, Neil Mitchell wrote: For example, in the module I'm currently working on: module Hoogle.DataBase.TypeSearch.Graph( Graph, newGraph, GraphResult(..), ArgPos, Binding, graphSearch ) where I dislike the fact that ,'s come after every line but the last - it lacks consistency, and often requires 1 more line of diff when adding somethign (add comma to previous line, and add the line). I would rather write: Also in the current syntax it is allowed to add a comma in the last line. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
Neil Mitchell wrote: Hi declaration with a regular syntax. For example: import Data.Map as Map unqualified (Map, (\\)) qualified (lookup, map, null) hiding (filter) I think I prefer this to my proposal, plus its closer to the current syntax. I think its also nearly equal to what Tom Davie came up with, given some keyword renaming. If we dropped the unqualified keyword, and just required unqualified things to come directly after, we get the full benefits of not introducing any keywords. We're still not introducing any keywords either way, fortunately :-). 'qualified', 'as' and 'hiding' are not keywords: the syntax after 'import' has no place for lowercase identifiers, so we can use as many new words as we want, here, as long as module names stay capitalized and import lists remain parenthesized (or, import lists could equally well be in layout after 'where', 'of', 'let' or 'do' if we adopt the layout syntax) -Isaac ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
On Wed, Jul 9, 2008 at 10:01 AM, Neil Mitchell [EMAIL PROTECTED] wrote: It seems that the qualified import syntax is a bit awkward. At the moment, its common to see: import qualified Data.Map as M import Data.Map(Map) i.e. import a module, give it an alias (M), and put some things in the current namespace (Map). Incidentally, I sometimes find myself writing this: import Data.Map (Map) ; import qualified Data.Map as M It's not perfect, but at least it lines up with my other imports a little better. Stuart ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] QuickCheck: outdated manual
Online QC manual[1] says[2] that 'vector' takes number of elements and generator, while in QuickCheck-1.1.0.0 it takes only number and generates vector of arbitrary's. Please fix that. By the way, I find the old version as useful as the new one. Although both are trivially implemented, I don't see any reason of why one is included and the other is not. Does anyone? 1. http://www.cs.chalmers.se/~rjmh/QuickCheck/manual.html 2. http://www.cs.chalmers.se/~rjmh/QuickCheck/manual_body.html#17 -- Roman I. Cheplyaka :: http://ro-che.info/ ...being in love is totally punk rock... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Interesting feature
2008/7/9 Yitzchak Gale [EMAIL PROTECTED]: David Overton wrote: Also, see my recent attempts at (constraint) logic programming in Haskell: http://overtond.blogspot.com/2008/07/pre.html http://overtond.blogspot.com/2008/07/haskell-sudoku-solver-using-finite.html See the Sudoku page on the wiki: http://www.haskell.org/haskellwiki/Sudoku Please add your solver there. I've done that. Thanks. David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to do a special kind of comment with the TokenParser
Hi,
TokenParser supports two kinds of comments, the multi-line comments (ie. {-
-}) and the single line comments (ie. -- \n).
The language I am trying to parse, however, has comments which are neither.
The -- acts like a single line comment which extends to the end of the line
usually, but can also be truncated to before the end of the line by another
--. For example:
noncomment -- comment comment
noncomment -- comment comment -- noncomment noncomment -- comment --
noncomment
noncomment
I haven't been able to get the TokenParser to work with this style of
comment. The best I could do was copy the whole Token module and modify the
code:
data LanguageDef st
= LanguageDef
{ {- snip -}
*, commentLine:: String*
{- snip -}
}
{- snip -}
makeTokenParser languageDef
= TokenParser{ {- snip -} }
where
{- snip -}
whiteSpace
| noLine noMulti = skipMany (simpleSpace *| customComment* ?
)
| noLine = skipMany (simpleSpace *| customComment* |
multiLineComment ? )
| noMulti= skipMany (simpleSpace *| customComment* |
oneLineComment ? )
| otherwise = skipMany (simpleSpace *| customComment* |
oneLineComment | multiLineComment ? )
where
noLine = null (commentLine languageDef)
noMulti = null (commentStart languageDef)
*customComment =
do{commentCustom languageDef
;return()
}*
Then I put my specialised comment parser in the customComment field:
languageDef = TOKEN.LanguageDef
{{- snip -}
, TOKEN.commentCustom = customComment
{- snip -}
}
where
customComment = do
string --
untilLineCommentEnd
return ()
untilLineCommentEnd = do
c - manyTill anyChar (string \n | try (string --))
return ()
Anyone know of a way I could reuse the TokenParser code rather than copy and
tweaking it?
Thanks
-John
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FPGA / Lava and haskell
On Wed, Jul 9, 2008 at 2:22 AM, Marc Weber [EMAIL PROTECTED] wrote: You're going to design something like that with an FPGA in it? :) The FPGA is only used for developement. If everything works fine I'd like to put it on the market. My hope is to get one low cost chip doing everything this way. Would you suggest using other tools? Ah, yes, it is common to develop on an FPGA before fabricating to, say, on ASIC . I'm still a total noob in this area So you plan on developing a chip or board without any previous hardware experience? Sounds challenging :). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: How to do a special kind of comment with the TokenParser
TokenParser seems to pose more problems than it solves. I think it is
usually easier to define your own scanner and avoid the necessary
Haskell language extensions used there. (Surely parts of the code from
TokenParser can be copied.)
Cheers Christian
John Ky wrote:
Hi,
TokenParser supports two kinds of comments, the multi-line comments (ie.
{- -}) and the single line comments (ie. -- \n).
The language I am trying to parse, however, has comments which are
neither. The -- acts like a single line comment which extends to the
end of the line usually, but can also be truncated to before the end of
the line by another --. For example:
noncomment -- comment comment
noncomment -- comment comment -- noncomment noncomment -- comment --
noncomment
noncomment
I haven't been able to get the TokenParser to work with this style of
comment. The best I could do was copy the whole Token module and modify
the code:
data LanguageDef st
= LanguageDef
{ {- snip -}
*, commentLine:: String*
{- snip -}
}
{- snip -}
makeTokenParser languageDef
= TokenParser{ {- snip -} }
where
{- snip -}
whiteSpace
| noLine noMulti = skipMany (simpleSpace *| customComment*
? )
| noLine = skipMany (simpleSpace *| customComment*
| multiLineComment ? )
| noMulti= skipMany (simpleSpace *| customComment*
| oneLineComment ? )
| otherwise = skipMany (simpleSpace *| customComment*
| oneLineComment | multiLineComment ? )
where
noLine = null (commentLine languageDef)
noMulti = null (commentStart languageDef)
*customComment =
do{commentCustom languageDef
;return()
}*
Then I put my specialised comment parser in the customComment field:
languageDef = TOKEN.LanguageDef
{{- snip -}
, TOKEN.commentCustom = customComment
{- snip -}
}
where
customComment = do
string --
untilLineCommentEnd
return ()
untilLineCommentEnd = do
c - manyTill anyChar (string \n | try (string --))
return ()
Anyone know of a way I could reuse the TokenParser code rather than copy
and tweaking it?
Thanks
-John
___
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] CAL (OpenQuark) and enterprise
Hi Haskellers and CALers, I have the feeling that a lot of code in my jee application can be done better by using functional programming. There is a lot of searching in object trees, transforming objects to another objects, aggregation functions... All written in java. Sequential logic can by done declarative with statemachines and workflows (not handcoded, dut drawed) all other with functions. Has somebody experience with this? Or is that a bad idea? Should I use pure functions, or imperative-functional language such as Scala? Is somebody here using CAL (OpenQuark) in jee application? What is your experience -- View this message in context: http://www.nabble.com/CAL-%28OpenQuark%29-and-enterprise-tp18366397p18366397.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
On Wed, 2008-07-09 at 12:36 +0200, Henning Thielemann wrote: On Wed, 9 Jul 2008, Neil Mitchell wrote: For example, in the module I'm currently working on: module Hoogle.DataBase.TypeSearch.Graph( Graph, newGraph, GraphResult(..), ArgPos, Binding, graphSearch ) where I dislike the fact that ,'s come after every line but the last - it lacks consistency, and often requires 1 more line of diff when adding somethign (add comma to previous line, and add the line). I would rather write: Also in the current syntax it is allowed to add a comma in the last line. GHC rejects this. (Or is that just for import lists?) jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] CAL (OpenQuark) and enterprise
Hi There is a lot of searching in object trees, transforming objects to another objects, aggregation functions... Sounds like you want: Either Uniplate: http://www-users.cs.york.ac.uk/~ndm/uniplate/ Or SYB: http://www.cs.vu.nl/boilerplate/ Read through both papers for various examples of what you might want to do, Should I use pure functions, or imperative-functional language such as Scala? On the Haskell list I think its fair to say everyone recommends you should use Haskell. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FPGA / Lava and haskell
marco-oweber: Is Haskell still used (in industry as well ?) to write (V)HDL code to program FPGAs and create circuits on chips? The Chalmers Lava homepage tells abouta Xilinx version which should be merged in soon. But on the xilinx homepage there was no reference to neither Lava nor haskell.. I'm thinking about designing a similar tool to www.combimouse.com. See also BlueSpec and Atom et al, http://funhdl.org/wiki/doku.php http://funhdl.org/wiki/doku.php?id=funhdlDokuWiki=fa52189d5ac4c0098c15ee324e0056ec ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
On Wed, Jul 9, 2008 at 1:03 AM, wren ng thornton [EMAIL PROTECTED] wrote: What I would like to see is the ability to do (1) module renaming, (2) qualified import, (3) unqualified import, and (4) hiding all in a single declaration with a regular syntax. For example: import Data.Map as Map unqualified (Map, (\\)) qualified (lookup, map, null) hiding (filter) I've often thought it would be for Haskell to steal Agda's module syntax. It does pretty much everything you want (plus some other stuff we maybe don't need) and the various things it does fit together logically. -- Dave Menendez [EMAIL PROTECTED] http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News: Issue 76 - July 9, 2008
--- Haskell Weekly News http://sequence.complete.org/hwn/20080709 Issue 76 - July 09, 2008 --- Welcome to issue 76 of HWN, a newsletter covering developments in the [1]Haskell community. The [2]ICFP Programming Contest is this weekend! Go forth and kick some butt, Haskell-style. A big thank you in advance to all those at PSU and U Chicago who are working hard to write and run the contest. Community News Luke Palmer (luqui) is [3]having a great time in Antwerp. John Goerzen's son is [4]so cute, it should be illegal. Announcements Haskell-cafe on lively.com. Edward Kmett has created a [5]Haskell Cafe room on Google's new virtual-world platform [6]Lively (which is unfortunately windows-only at the moment). Uniplate 1.2. Neil Mitchell [7]announced the release of [8]Uniplate 1.2, a library for reducing boilerplate code by performing generic traversals. Version 1.2 features some bug fixes, a compatibility layer with Compos and SYB, and a 25-50% performance increase over Uniplate 1.0. GHC 6.8.2 stable in Gentoo. Luis Araujo [9]announced that GHC 6.8.2, and its accompanying libraries, have now been marked as stable in the official Gentoo portage tree. The Monad.Reader (11) - Call for Copy. Wouter Swierstra [10]announced a call for copy for Issue 11 of [11]the Monad.Reader. The submission deadline is August 1, although you should let Wouter know as soon as possible if you plan to submit something. hCsound. John Lato [12]announced the initial public release of [13]hCsound, a Haskell binding to the Csound audio processing language API. Portland and OSCon. John Goerzen [14]inquired whether any Haskellers in Portland would be interested in getting together during OSCon July 23 or 24. Faster graph SCCs. Iavor Diatchki [15]announced that he has implemented Tarjan's algorithm for computing the strongly connected components of a graph, which is considerably faster than the containers package for larger graphs. Iavor's implementation is available in the [16]GraphSCC package. parallel map/reduce. jinjing [17]exhibited some code for doing parallel map/reduce computations. Disciplined Disciple Compiler. Ben Lippmeier [18]announced version 1.1 of the [19]Disciplined Disciple Compiler (DDC), an explicitly lazy dialect of Haskell, with support for first class destructive update of arbitrary data, computational effects without the need for state monads, and type directed field projections. Version 1.1 includes a number of new features and more example code. darcs 2.0.2. David Roundy [20]announced the release of [21]darcs 2.0.1 and 2.0.2. These releases fix quite a few bugs, and users of darcs 2 are strongly recommended to upgrade. Google Summer of Code Progress updates from participants in the 2008 [22]Google Summer of Code. GHC plugins. Max Bolingbroke is working on dynamically loaded plugins for GHC. Over the [23]past two weeks, he has implemented type safe dynamic loading, an annotations system, and some sample plugins. Hoogle 4. Neil Mitchell (ndm) is working on [24]Hoogle 4. [25]This week, he has been working on type searching, using a much more efficient algorithm than type search in previous versions of Hoogle. Next week, he plans to finish off type search and work on the build system. DPH physics engine. Roman Cheplyaka (Feuerbach) is working on a [26]physics engine using [27]Data Parallel Haskell. He spent most of [28]this week fixing bugs and improving existing simulation code. And he now has something to [29]show for it! Language.C. Benedikt Huber (visq) is [30]working on Language.C, a standalone parser/pretty printer library for C99. [31]This week, he created a semantic representation for declarations and types, and a way to convert between an AST representation and a semantic representation. Cabal dependency framework. Andrea Vezzosi (Saizan) is working on a [32]make-like dependency analysis framework for Cabal. Generic tries. Jamie Brandon is working on a library for efficient maps using generalized tries. GHC API. Thomas Schilling (nominolo) is working on [33]improvements to the GHC API. Libraries Proposals and extensions to the [34]standard libraries. Extensible exceptions. Ian Lynagh sent out a [35]proposal to replace the current exception mechanism in the base library with extensible exceptions, a la Simon Marlow's [36]extensible extensions paper. Deadline for discussion is 25th July. Discussion Qualified import syntax badly designed (?). Neil Mitchell began a [37]discussion about Haskell syntax for qualified module imports (and module imports in general). Trouble with zip12. Michael Feathers is [38]having trouble
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
David Menendez [EMAIL PROTECTED] wrote: I've often thought it would be for Haskell to steal Agda's module syntax. It does pretty much everything you want (plus some other stuff we maybe don't need) and the various things it does fit together logically. What does that look like? I've been looking for some kind of documentation for ~20 minutes and I still can't find an example of an import. -- _jsn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] CAL (OpenQuark) and enterprise
On Wed, Jul 9, 2008 at 6:28 PM, Neil Mitchell [EMAIL PROTECTED] wrote: On the Haskell list I think its fair to say everyone recommends you should use Haskell. Not necessarily. If the OP has a significant body of existing Java code (s)he has to work with (which is what the question suggests) then Scala would most likely be a very good place to look. Cheers, Miles ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
On Wed, Jul 9, 2008 at 2:51 PM, Jason Dusek [EMAIL PROTECTED] wrote: David Menendez [EMAIL PROTECTED] wrote: I've often thought it would be for Haskell to steal Agda's module syntax. It does pretty much everything you want (plus some other stuff we maybe don't need) and the various things it does fit together logically. What does that look like? I've been looking for some kind of documentation for ~20 minutes and I still can't find an example of an import. There's a description on their wiki at http://appserv.cs.chalmers.se/users/ulfn/wiki/agda.php?n=Docs.ModuleSystem. There's a longer description in chapter 4 of Ulf Norell's thesis, http://www.cs.chalmers.se/~ulfn/papers/thesis.pdf, which may be slightly out of date. Essentially, the import statement in Agda brings a module from another file into scope as if it were a sub-module in the current file. It also lets you rename the module, in case it conflicts with another name. It does not bring any values or types into scope; they are accessed by qualified names. import Some.Module import Some.Other.Module as SOM A separate statement lets you bring names from any module into the current scope. You can provide a list of names to include or exclude, and a list of names to rename. open SOM using (x,y) open SOM renaming (x as alsoX, y as alsoY) open SOM hiding (x,y) You can combine renaming with using or hiding, but you can't use using or hiding together. Note that hidden names are still accessible as qualified names. That is, if you open SOM hiding x, you can still say SOM.x. There's also a short-hand form that lets you import a module and open it on the same line. Aside from the syntax differences, Agda's module system features nested modules and parameterized modules, both of which could be pretty handy in Haskell. Nested modules allow libraries which have many modules with similar names to use qualified names. open import Gtk using (module Button, module Window) f = ... Button.name ... Window.name ... Parameterized modules work sort of like implicit arguments. I suspect that having them in Haskell could eliminate most of the call for things like top-level IORefs. -- Dave Menendez [EMAIL PROTECTED] http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
re: [Haskell-cafe] Swapping Monads
Dominic, You can also reference Eugenia Cheng's paper on arXivhttp://arxiv.org/abs/0710.1120 . Best wishes, --greg -- L.G. Meredith Managing Partner Biosimilarity LLC 806 55th St NE Seattle, WA 98105 +1 206.650.3740 http://biosimilarity.blogspot.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Qualified import syntax badly designed (?)
David Menendez [EMAIL PROTECTED] wrote: Jason Dusek [EMAIL PROTECTED] wrote: David Menendez [EMAIL PROTECTED] wrote: I've often thought it would be for Haskell to steal Agda's module syntax. What does that look like? I've been looking for some kind of documentation for ~20 minutes and I still can't find an example of an import. There's a description on their wiki at http://appserv.cs.chalmers.se/users/ulfn/wiki/agda.php?n=Docs.ModuleSystem. Thanks. That system is pretty neat -- I wish we had it. Without parameterized modules, we are reduced to a kind of warty singleton pattern -- or IORefs, as you mention. -- _jsn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Combining Wouter's expressions with extensible records
Well, my extension of Wouter's datatypes proved to be unweildy So, I'm trying to use http://fmapfixreturn.wordpress.com/2008/05/03/simple-extensible-records-now-quick-generic-tricks-pt-1/ for extensible records. I ran across my first problem rather quickly! data Expr f = In (f (Expr f)) Ok, but to make it part of a record, it needs to implement Data: data Expr f = In (f (Expr f)) deriving Data but this gives No instances for (Data (f (Expr f)), Typeable (Expr f)) arising from the 'deriving' clause of a data type declaration at Planning/Wouter.hs:77:0-42 Any hints? Thanks, -Ron ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Combining Wouter's expressions with extensible records
On Wed, Jul 9, 2008 at 9:40 PM, Ron Alford [EMAIL PROTECTED] wrote: Ok, but to make it part of a record, it needs to implement Data: data Expr f = In (f (Expr f)) deriving Data but this gives No instances for (Data (f (Expr f)), Typeable (Expr f)) arising from the 'deriving' clause of a data type declaration at Planning/Wouter.hs:77:0-42 The Data class has a requirement that any instances are also instances of Typeable, so you'd really want data ... = ... deriving (Data, Typeable) Except that I couldn't derive Typeable for your particular data type. It isn't immediately obvious to me that the Typeable family of classes deal at all with higher-kinded type constructors, but I didn't look that hard. -Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Lazy IO
Suppose I have a lazy function f :: [Int] - [Int], and I happen to know that for all n, the n-th element of the output may only depend on the first (n-1) elements of the input. I want to print a number from f's output list, and then ask the user for the next number in f's input list, and then loop until the user stops providing valid numbers. I also need to be able to do IO after my loop exits. Consider the following code: -- module Main where import Control.Monad.Fix import System.IO.Unsafe promptInt :: String - IO (Maybe Int) promptInt p = do putStr p s - getLine let rs = reads s if not $ null rs then return $ Just $ fst $ head rs else return $ Nothing promptInts :: [String] - IO [Int] promptInts [] = return [] promptInts (p:ps) = do m - promptInt p case m of Just n - do ns - unsafeInterleaveIO $ promptInts ps return $ n:ns Nothing - return [] -- assume accumulator is an opaque function accumulator :: [Int] - [Int] accumulator = scanl (+) 0 makeAccPrompt :: Int - String makeAccPrompt n = [Acc = ++ show n ++ ] ? main :: IO () main = do xs - mfix $ promptInts . map makeAccPrompt . accumulator seq (length xs) $ print xs -- Question: If I can't change my function f (in this case, accumulator), then is it possible to get the effect I want without having to resort to unsafeInterleaveIO? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Profiling nested case
Hi! I am making a simple raycasting engine and have a function which take a point in space and return a color of an object (if there is any) at this point in space. And because the whole thing is really slow (or was really slow) on simple examples I decided to profile it. It takes around 60 seconds for a 640x480 px image with 400 depth of field. This is at worst 122,880,000 calculations (if the scene is rather empty) of a coordinate of a point in space and then checking for a color. And 60 seconds look really a lot to me for that. So I went profiling and found out that the strange part of code is the main color checking function which has a list of objects (at this time the list is hardcoded). It looks like this: world :: SpacePoint - VoxelColor world point = case msum . sequence elements $ point of Just v - v Nothing - noColor where elements = [redSphere (0,50,0) 50, greenSphere (25,-50,0) 50, blueSphere (-150,0,150) 50] So three spheres in a world and I check if the point is in any of them. Like that: sphere :: SpacePoint - BasicReal - VoxelColor - WorldElement -- center of sphere, it's radius, it's color sphere (x0,y0,z0) r color (x,y,z) | x' * x' + y' * y' + z' * z' = r * r = Just color | otherwise= Nothing where x' = x - x0 y' = y - y0 z' = z - z0 redSphere :: SpacePoint - BasicReal - WorldElement redSphere c r = sphere c r redColor So profiling told me that world function takes 38.4 % of all running time. So I decided to play with it. Maybe a more direct approach would be better: world :: SpacePoint - VoxelColor world point = findColor [redSphere (0,50,0) 50, greenSphere (25,-50,0) 50, blueSphere (-150,0,150) 50] where findColor [] = noColor findColor (f:fs) = case f point of Just v - v Nothing - findColor fs Great, it improved. To 40 s. But still it was too much. I tried this: world :: SpacePoint - VoxelColor world point = case redSphere (0,50,0) 50 point of Just v - v Nothing - case greenSphere (25,-50,0) 50 point of Just v - v Nothing - case blueSphere (-150,0,150) 50 point of Just v - v Nothing - noColor And it took 15 s. And also the profiling was like I would anticipate. Calculating points coordinates and checking spheres takes almost all time. So any suggestions how could I build a list of objects to check at runtime and still have this third performance? Why this big difference? (I am using GHC 6.8.3 with -O2 compile switch.) (The * operator is casting a ray, that is multiplying a ray direction vector with a scalar factor.) Mitar Main-case.prof Description: Binary data Main-rec.prof Description: Binary data Main-seq.prof Description: Binary data ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Lazy IO
On 7/9/08, Ronald Guida [EMAIL PROTECTED] wrote: Question: If I can't change my function f (in this case, accumulator), then is it possible to get the effect I want without having to resort to unsafeInterleaveIO? Yes, but you won't like it. Since you know that (f xs !! n) only depends on the first (n-1) elements of xs, you have this identity: f xs !! n == f (take (n-1) xs) !! n You can then call f with a new list each time, extracting the desired elements as you build up the source list. This is, of course, terribly inefficient. In order to see why you need an unsafe primitive to solve this function, you may find it enlightening to try to write this function: data Stream a b = NilStream | Stream b (a - Stream a b) liftStream :: ([a] - [b]) - Stream a b liftStream = ? (the inverse of this function is trivial to write) The problem is that there is no way to extract the continuation from f (x:??); if you had some way, you'd be able to call the same continuation multiple times with different arguments, effectively pausing f partway through and giving it new input. By using unsafeInterleaveIO, you are adding a side-effect to the pure argument to f, which allows it to interact with the user. Once that side-effect executes, the value is 'fixed' into place and can't be modified. Another way to look at it is to suppose that f didn't meet your invariant, and tried to access an element out of order. How is the thunk to be evaluated for that element built? If it can't do IO, it must be a pure computation. But it needs to do IO because the element hasn't been determined yet. -- ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
