Re: [Haskell-cafe] implementing a csv reader
On Tue, 2006-08-22 at 11:59 +0200, Tamas K Papp wrote: On Tue, Aug 22, 2006 at 11:26:45AM +0200, Henning Thielemann wrote: See also http://www.xoltar.org/languages/haskell.html http://www.xoltar.org/languages/haskell/CSV.hs Thanks. Haskell is incredibly neat ;-) Now I need to find something else for practice. Is there anything related to data analysis/statistics that is lacking is Haskell? Best, Tamas Maybe a crosstab app? Say, read in some csv data and do a crosstab of it. I was looking at doing one myself quite a while back, but I'm an *ultra-newbie* when it comes to Haskell, and such an app would be a real handful for me... :-) I don't know if it'll help at all (as Python is very different to Haskell) but here's a link to a Python recipe which does this - http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/334695 A Haskell equivalent would (imo) be a *great* example/appetiser for Haskell. Very useful for newbies too, as even for a simple thing like reading data line-by-line, it's really useful to have an easy-to-understand example. A crosstab app mightn't be that easy to _do_, but I think it would be easy to understand. Just my 2c worth ... - Andy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: type synonym liberalization (was class [] proposal)
Hello Arie, Wednesday, August 23, 2006, 2:54:54 AM, you wrote: With the proper interpretation, type synonyms like type ABlockStream = BlockStream b = b type AMemoryStream = MemoryStream m = m How does your proposal compare to introducing existential types proper? As in type ABlockStream = exists b. BlockStream b = b existential variables pack dictionary inside the data item (object) itself, like in the OOP languages. so this the _semantic_ change. Brandon's idea is just _syntax_ sugar, one of the possible ways to simplify writing of signatures for regular Haskell polymorphic functions, what pass dictionaries apart of objects read the http://haskell.org/haskellwiki/OOP_vs_type_classes and look for existential there -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Re: Memoizing longest-common-subsequence
From: Jared Updike [mailto:[EMAIL PROTECTED] Thanks for posting the code. It works on pretty large data sets (for example, a thousand Strings each) and I have a hunch that if I use Data.ByteString it would even work fast enough on my quarter meg text files (split on words, ~40,000 and ~50,000 words each) to use in place of GNU sdiff or diff. Did you use FastPackedString or ByteString to get performance you alluded to? You'll notice that the primary interface is: diff :: Eq a = [a] - [a] - [Modification a] So it's not optimised for any kind of String input. The performance I'm alluding to is not something I've tested with any rigor, or even metrics to support. I simply needed to compare a couple of large text files which GNU diff didn't handle (I think when the input is over a certain size it breaks it into chunks and diffs the chunks). I tried this code, and it did the job in a reasonable time (my PC has 1G of memory, and that helps when the input lists have to reside entirely in memory). That was using naïve String-IO too, so there might well be some mileage in a FPS-specific implementation. I profiled the code by generating large inputs in memory, and then invoking the various interfaces, so as to isolate the testing from IO performance. And that was just to find the performance hotspots in the algorithm, not to compare against other diff implementations. Alistair * Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. * ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: class [] proposal Re: [Haskell-cafe] One thought: Num to 0as ? to list?
it's because you not programmed a lot with type classes. if you
start, you will soon realize that type signatures with classes are
just unreadable. just look at sources of my streams library
copyStream :: (BlockStream h1, BlockStream h2, Integral size)
= h1 - h2 - size - IO ()
I know this is probably just a personal preference, but I have to say
that this syntax (the canonical Haskell'98 one) is by far the most
readable and instantly clear of any of the alternatives that have been
suggested in this thread:
copyStream :: BlockStream* - BlockStream** - Integral - IO ()
Here you have invented a new notation for type variables (* and **),
when we already have a perfectly good one.
copyToMemoryStream :: BlockStream - MemoryStream - Integral - IO ()
Whereas here, the lack of any type variable means I am no longer aware
that overloading is going on. This is likely to discourage the reuse of
this code fragment, rather than encourage it.
copyStream :: {BlockStream} h1 - {BlockStream} h2
- {Integral} size - IO ()
What is gained by attaching the constraints inline with the type
variables? If the type variable occurs more than once, which occurrence
should I attach the constraint to? What if I attach different
constraints to different occurrences of the same variable? (Obviously
the union is intended, but writing constraints in several different
locations would be highly confusing). But at least there is a syntactic
marker ({}) that overloading is happening.
copyStream :: {BlockStream} - {BlockStream} - {Integral} - IO ()
Again, omitting type variables means that the possible mental confusion
over whether the two {BlockStream} constraints apply to the same
implicit variable or to different ones is unpleasant. Better to be
fully explicit, after all, it only takes one extra character to name the
variable!
foo :: Collection c a = a - c
=== foo :: {Collection c} a - c
foo :: Collection c a = c - c
=== foo :: {Collection * a} c - c
forall a. Num a = (forall b. (Coll b a, Ord b) = b a - ()) - ()
=== (forall b. {Coll * a, Ord}b{Num}a - ())- ()
=== forall a. (forall b. ({Coll * a, Ord} b) ({Num} a) - ()) - ()
The lengths people will go to in making things difficult for the reader,
just to save a few characters is truly amazing. Remember, the code will
be read many more times than it is written. IMHO, the various proposed
sugar adds nothing helpful, and just muddies understanding.
Regards,
Malcolm
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Re[2]: [Haskell-cafe] Re: Memoizing longest-common-subsequence
Hello Alistair, Wednesday, August 23, 2006, 1:43:30 PM, you wrote: I've found the folder in which I did some of this testing, and GNU diff has no problem with the input files; they're only 7M, My program spends 70% of its time doing String-IO (so 30% in the algorithm), and peaks at about 350M of memory (which seems quite high, but then it does convert the String input into STArrays). The algorithm itself takes about 18secs on this input (wall-clock time), but the profile says a lot less CPU time is used. I think using ByteStrings would be a big improvement; maybe I'll find time to try that later. as variant, you can try streams library - it's several times faster for line-oriented I/O. another solution that can also speed up your code, although not so much, is to use hGetContents and then 'lines' http://haskell.org/haskellwiki/Library/Streams http://www.haskell.org/library/StreamsBeta.tar.gz -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: class [] proposal Re: [Haskell-cafe] One thought: Num to 0as ? to list?
On Wed, Aug 23, 2006 at 01:28:57PM +0100, Malcolm Wallace wrote: The lengths people will go to in making things difficult for the reader, just to save a few characters is truly amazing. Remember, the code will be read many more times than it is written. IMHO, the various proposed sugar adds nothing helpful, and just muddies understanding. Seconded. If someone just wants to type less characters, the he/she can omit most of type signatures. I haven't used any IDE for Haskell (like VisualHaskell), but it would be nice if it could fill the missing type signatures automatically. In cases when monomorphism restriction kicks in, it could also present the type that would be inferred with MR turned off. Best regards Tomasz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: class [] proposal Re: [Haskell-cafe] One thought: Num to 0as ? to list?
tomasz.zielonka: On Wed, Aug 23, 2006 at 01:28:57PM +0100, Malcolm Wallace wrote: The lengths people will go to in making things difficult for the reader, just to save a few characters is truly amazing. Remember, the code will be read many more times than it is written. IMHO, the various proposed sugar adds nothing helpful, and just muddies understanding. Seconded. If someone just wants to type less characters, the he/she can omit most of type signatures. I haven't used any IDE for Haskell (like VisualHaskell), but it would be nice if it could fill the missing type signatures automatically. In cases when monomorphism restriction kicks in, it could also present the type that would be inferred with MR turned off. I use the following script from vim to infer top level type declarations for me. I've found it particularly useful for understanding others' code: #!/bin/sh # input is a top level .hs decls FILE=$* DECL=`cat` ID=`echo $DECL | sed 's/^\([^ ]*\).*/\1/'` echo :t $ID | ghci -v0 -cpp -fglasgow-exts -w $FILE echo $DECL Saved to 'typeOf', you can bind it from vim with: :map ty :.!typeOf %^M in your .vimrc So, from vim the following source: f (x,y,z) a b = y + a + b hit, 'ty' and its replaced with: f :: forall b c a. (Num b) = (a, b, c) - b - b - b f (x,y,z) a b = y + a + b I imagine it would be possible to bind from emacs with little effort. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Proposal to allow {} instead of () in contexts
Hi -
Disregarding my last proposal which involved the use of {} in types, I am
wondering if anyone would agree with me that it would be a good idea to use
{} instead of () when writing out the context ie:
foo :: (Num a, Bar a) = a - a
would become:
foo :: {Num a, Bar a} = a - a
and the same for every other situation in the language where a context
appears.
My reasons are twofold:
1) The context is supposed to be understood (afaiu) as a *set* of
constraints not a *tuple* of constraints (ie what relevance does the
ordering implied by the tuple notation have here?), so the using of set
braces seems mathematically more appropriate
2) It would allow an editor to give the correct fontification for an
incomplete type expression. At the moment, if you'd just typed:
foo :: (Bar
the editor would have no way of knowing if Bar is a classcon or a tycon,
whereas with:
foo :: {Bar
the opening brace immediately informs the editor that the following text
should be parsed as a context and so it could fontify Bar appropriately.
For backwards compatibility the use of () could still be supported - braces
don't occur in H98 in the positions I'm proposing to allow them so nothing
would be broken.
Regards, Brian.
--
Logic empowers us and Love gives us purpose.
Yet still phantoms restless for eras long past,
congealed in the present in unthought forms,
strive mightily unseen to destroy us.
http://www.metamilk.com
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[Haskell-cafe] extreme newbie: hugs prompt vs load module
[linux, ghci 6.4.3.20060820, hugs May 2006] I have just started learning Haskell. I have hugs and ghci under linux, and I'm going through the Gentle Introduction to Haskellhttp://www.haskell.org/tutorial, so far through section 4, case expressions and pattern matching. I'm a python programmer, with background in maclisp, scheme, T, C, C++, and a little J. I'm confused about what sort of things I can type at the interpreter prompt, and what things have to be loaded as a module. I keep trying to treat the prompt like a lisp or python REPL, which is obviously wrong. Can someone set me straight? Is there another tutorial that might be more appropriate for me? I am finding haskell quite appealing. I hope to start writing real (if small) applications to do some data analysis from our Postgres DB. Any hints? --George Young -- Are the gods not just? Oh no, child. What would become of us if they were? (C.S. Lewis) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] extreme newbie: hugs prompt vs load module
On Aug 23, 2006, at 10:16 AM, George Young wrote: [linux, ghci 6.4.3.20060820, hugs May 2006] I have just started learning Haskell. I have hugs and ghci under linux, and I'm going through the Gentle Introduction to Haskellhttp://www.haskell.org/tutorial, so far through section 4, case expressions and pattern matching. I'm a python programmer, with background in maclisp, scheme, T, C, C++, and a little J. I'm confused about what sort of things I can type at the interpreter prompt, and what things have to be loaded as a module. I keep trying to treat the prompt like a lisp or python REPL, which is obviously wrong. Can someone set me straight? For the most part, the things you can enter at the GHCi or Hugs prompt are _expressions_. This mostly* excludes _declarations_, which are things like function definitions, datatype declarations, class and instance declarations, etc. Those things need to go into a source file. (*) 'let' expressions will allow you to define local functions as part of an expression, however. GHCi also has a slight variation of 'let' that allows you to define functions for the session. Is there another tutorial that might be more appropriate for me? The following tutorial is generally recognized as one of the better ones: http://www.cs.utah.edu/~hal/htut/ I am finding haskell quite appealing. I hope to start writing real (if small) applications to do some data analysis from our Postgres DB. Any hints? There are several haskell database layers. I've had some luck with HDBC, which has a PostgreSQL driver. http://quux.org:70/devel/hdbc --George Young -- Are the gods not just? Oh no, child. What would become of us if they were? (C.S. Lewis) Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: class [] proposal Re: [Haskell-cafe] One thought: Num to 0as ? to list?
On Wed, Aug 23, 2006 at 11:11:59PM +1000, Donald Bruce Stewart wrote: So, from vim the following source: f (x,y,z) a b = y + a + b hit, 'ty' and its replaced with: f :: forall b c a. (Num b) = (a, b, c) - b - b - b f (x,y,z) a b = y + a + b Nice! Best regards Tomasz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal to allow {} instead of () in contexts
On 8/23/06, Brian Hulley [EMAIL PROTECTED] wrote:
Hi -Disregarding my last proposal which involved the use of {} in types, I amwondering if anyone would agree with me that it would be a good idea to use{} instead of () when writing out the context ie:
foo :: (Num a, Bar a) = a - awould become:foo :: {Num a, Bar a} = a - aand the same for every other situation in the language where a contextappears.My reasons are twofold:
1) The context is supposed to be understood (afaiu) as a *set* ofconstraints not a *tuple* of constraints (ie what relevance does theordering implied by the tuple notation have here?), so the using of set
braces seems mathematically more appropriateI just started programming in Haskell again recently and I cannot even think of a case where any kind of brackets should be necessary. In the report [1], it clearly shows that a context is always followed by =. Are the parantheses just used to reduce lookahead requirements for parsers? If so, perhaps the parentheses should be made optional to make them easier to read for people. Plus, then there would not be any tuple vs. set confusion.
BTW, at least GHC allows duplicates in the context, like [ foo :: (Num a, Num a) = a - a ], so I don't know if calling it a set is really appropriate either.
2) It would allow an editor to give the correct fontification for anincomplete type _expression_. At the moment, if you'd just typed:foo :: (Barthe editor would have no way of knowing if Bar is a classcon or a tycon,
whereas with:foo :: {Barthe opening brace immediately informs the editor that the following textshould be parsed as a context and so it could fontify Bar appropriately.What about [ foo :: Bar ] when typing [ foo :: Bar a = a - a ]? It would be a mistake to require the grouping symbols even when there is only one element in the context. I think that the editor has to be know enough about the program to distinguish classes and type constructors without any grouping symbol requirement.
- Brian
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Re: [Haskell-cafe] extreme newbie: hugs prompt vs load module
George Young wrote: [linux, ghci 6.4.3.20060820, hugs May 2006] I have just started learning Haskell. I have hugs and ghci under linux, and I'm going through the Gentle Introduction to Haskellhttp://www.haskell.org/tutorial, so far through section 4, case expressions and pattern matching. I'm a python programmer, with background in maclisp, scheme, T, C, C++, and a little J. I'm confused about what sort of things I can type at the interpreter prompt, and what things have to be loaded as a module. I keep trying to treat the prompt like a lisp or python REPL, which is obviously wrong. Can someone set me straight? GHCi allows expressions, plus anything valid as a statement in a do block (of IO). That's why you can use let without an in clause to make bindings that stick around - you're getting the let form allowed in do blocks. You can also bind use the arrow bindings, to get result out of IO actions, like some_even - fmap (*2) randomIO. (isn't this a good answer to the perennial newbie question how do I get a out of IO a?) I usually work with GHCi (ghci MyModdule.hs) next to an editor, examining things in GHCi, then changing the code or adding things like data type declarations that can't be done interactively, and reloading the file (with :r). It works pretty well, though copying important declarations from the session into the module to preserve them across a reload is a bit annoying. The usual approach of making a REPL accept any valid code in the language wouldn't work so well for Haskell. It would be tough to implement, because declarations can come in any order, and extremely aggravating to use, because declarations can't be shadowed. Allowing class and type declarations interactively would be nice (perhaps Hugs already does?), but not a massive improvement alone. Maybe if there were a feature to extract all the code necessary to reproduce some interactively defined value? Brandon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] extreme newbie: hugs prompt vs load module
Hello George, Wednesday, August 23, 2006, 6:16:12 PM, you wrote: I'm confused about what sort of things I can type at the interpreter prompt, and what things have to be loaded as a module. I keep trying to treat the prompt like a lisp or python REPL, which is obviously wrong. Can someone set me straight? in hugs you can only type expressions: such as 2*2 or prod [1..10]. although there is a trick what sometimes help: let fac n = prod [1..n] in fac n it's also an expression, after all :) in ghci you can define functions with 'let' you can find more information about this in appropriate user guides, what is part of your installations and is also available online Is there another tutorial that might be more appropriate for me? yet another haskell tutorial commonly considered as more gentle than gentle introduction you can find Getting started and Books and tutorials links on the haskell.org. First page includes the most recommended books/tutorials while second contains more detailed explanations about their contents I am finding haskell quite appealing. I hope to start writing real (if small) applications to do some data analysis from our Postgres DB. Any hints? haskell.org - libraries and tools - databases -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] extreme newbie: hugs prompt vs load module
You can always load things inside ghci with: :m i.e. Prelude :m List Prelude List :m Control.Concurrent Prelude Control.Concurrent :m Control.Concurrent List Prelude List Control.Concurrent George Young wrote: [linux, ghci 6.4.3.20060820, hugs May 2006] I have just started learning Haskell. I have hugs and ghci under linux, and I'm going through the Gentle Introduction to Haskellhttp://www.haskell.org/tutorial, so far through section 4, case expressions and pattern matching. I'm a python programmer, with background in maclisp, scheme, T, C, C++, and a little J. I'm confused about what sort of things I can type at the interpreter prompt, and what things have to be loaded as a module. I keep trying to treat the prompt like a lisp or python REPL, which is obviously wrong. Can someone set me straight? Is there another tutorial that might be more appropriate for me? I am finding haskell quite appealing. I hope to start writing real (if small) applications to do some data analysis from our Postgres DB. Any hints? --George Young ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] implementing a csv reader
L.S.,
Reading and writing a comma seperated datafile doesn't have to be that
complicated; the following is an easy way to read a CSV file into a list
of tuples and display the list on screen:
displayTuples =
do
csvData - readFile data.csv
putStrLn $ unlines $ map (show . readTuple) $ lines csvData
readTuple :: String - (Int, Bool, String)
readTuple line = read tuple
wheretuple = '(' : line ++ )
If the file data.csv contains the following:
1, True, Festina lente
2, False, Carpe diem
displayTuples displays:
(1,True,Festina lente)
(2,False,Carpe diem)
Writing a list of tuples to a CSV file is even simpler:
writeTuples file tuples = writeFile file $ unlines $ map (tail . init .
show) tuples
The call:
writeTuples new.csv [(1, 'a'), (2, 'b')]
results in a file containg:
1,'a'
2,'b'
(without the leading spaces)
Met vriendelijke groet,
Henk-Jan van Tuyl
--
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On Tue, 22 Aug 2006 11:19:35 +0200, Tamas K Papp [EMAIL PROTECTED]
wrote:
Hi,
Now that I have read the tutorials, I think that the best way to learn
Haskell would be to use the language and write something simple yet
useful. I noticed that Haskell lacks a module for reading/writing csv
(comma separated value) files, so I thought I could implement that.
Questions:
1. Please tell me if you know of a csv module, because then I would do
something else.
2. I am looking for a parser, but I don't know Haskell parsers. Is
Parsec a good choice?
Thanks,
Tamas
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Re: [Haskell-cafe] implementing a csv reader
On Aug 23, 2006, at 3:37 PM, Henk-Jan van Tuyl wrote: L.S., Reading and writing a comma seperated datafile doesn't have to be that complicated; the following is an easy way to read a CSV file into a list of tuples and display the list on screen: For every complex problem, there is a solution which is simple, neat, and wrong. -- HL Mencken Although it seems straightforward at first, CSV suffers from text escaping complexities, just as does every other general purpose plain- text encoding. Most notably, a newline embedded inside double quotes does not end a record. These issues cause ugly corner cases if you aren't expecting them. And that's just the issues with moving tables of strings around; if those fields have non-string interpretations (dates or numbers or what have you), things get really hairy. To do the right thing probably requires perl-ish duck typing :-p See http://www.creativyst.com/Doc/Articles/CSV/CSV01.htm for a semi- authoritative reference on CSV. A related RFC is here: http:// tools.ietf.org/html/rfc4180 Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cabal question, adding data files
Hi, I have a cabal executable, which requires additional data files. How do I do this in Cabal? I have seen extra-source-files, but they are not added at install time to the destination directory, which doesn't help me. I noticed that Alex does this, but with a lot of Cabal calling in Setup.hs with hooks etc, which is not really ideal. Is there any easy way to do the install these files along with the program, please ? If anyone needs any concrete examples, take for example HsColour, which needs the files .hscolour and hscolour.css, but currently install doesn't put either of them anywhere useful. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal question, adding data files
On Wed, Aug 23, 2006 at 10:42:54PM +0100, Neil Mitchell wrote: I have a cabal executable, which requires additional data files. How do I do this in Cabal? I have seen extra-source-files, but they are not added at install time to the destination directory, which doesn't help me. The field you want is data-files, documented in section 2.1.1 of the Cabal User's Guide. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal question, adding data files
Hi The field you want is data-files, documented in section 2.1.1 of the Cabal User's Guide. That looks perfect. Is there any reason that Alex doesn't use this? I was trying to learn by example. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: class [] proposal Re: [Haskell-cafe] One thought: Num to 0as ? to list?
On 8/23/06, Donald Bruce Stewart [EMAIL PROTECTED] wrote: I use the following script from vim to infer top level type declarationsfor me. I've found it particularly useful for understanding others' code:delurkOn the topic of coding Haskell with Vim is there an indentation plugin for Haskell available? Google hasn't found one for me and none ismentioned on the Haskell wiki.Thanks,Toby. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal to allow {} instead of () in contexts
On August 23, 2006 5:16 PM, Brian Smith wrote
On 8/23/06, Brian Hulley [EMAIL PROTECTED] wrote:
Hi -
Disregarding my last proposal which involved the use of {} in types, I am
wondering if anyone would agree with me that it would be a good idea
to use {} instead of () when writing out the context ie:
foo :: (Num a, Bar a) = a - a
would become:
foo :: {Num a, Bar a} = a - a
1) The context is supposed to be understood (afaiu) as a *set*
I just started programming in Haskell again recently and I cannot even
think of a case where any kind of brackets should be necessary. In the
report [1], it clearly shows that a context is always followed by =.
Are
the parantheses just used to reduce lookahead requirements for
parsers? If so, perhaps the parentheses should be made optional to
make them easier to read for people. Plus, then there would not be any
tuple vs. set confusion.
Also, parens should not be needed in
data D = D | E deriving Eq, Ord
because a data decl can never be confused with a tuple component. It would
certainly be very much neater to not have to use parens just because there
is more than one constraint / deriving class.
Certainly the current need for parens in these situations seems like a wart
and always trips me up.
BTW, at least GHC allows duplicates in the context, like [ foo :: (Num a,
Num a) = a - a ], so I don't know if calling it a set is really
appropriate either.
I'd argue that this is precisely what makes the above a set rather than a
tuple: {Num a, Num a} === {Num a}
Also, I'd argue that an error should be given when a constraint is
duplicated because it has no meaning thus probably indicates some
misunderstanding on the part of the programmer (unless the idea is to pave
the way for class aliases where one may want to write code that can compile
under different alias environments).
2) It would allow an editor to give the correct fontification for an
incomplete type expression. At the moment, if you'd just typed:
foo :: (Bar
the editor would have no way of knowing if Bar is a classcon or a
tycon, whereas with:
foo :: {Bar
the opening brace immediately informs the editor that the following text
should be parsed as a context and so it could fontify Bar appropriately.
What about [ foo :: Bar ] when typing [ foo :: Bar a = a - a ]?
It would be a mistake to require the grouping symbols even when there
is only one element in the context. I think that the editor has to be know
enough about the program to distinguish classes and type constructors
without any grouping symbol requirement.
If braces were used even in the case where there was only one constraint the
= would never be needed as in:
foo :: {Bar a} a-a
so there would be no more characters to type yet the notation would have the
advantage that the signature could be understood by itself without requiring
the user to have already defined Bar somewhere.
I was also thinking that in:
foo :: {Ba
Ba could be fontified as a classcon to help the user realise that he/she is
typing a classcon at that point. However it also could be helpful to only
fontify known tycons/classcons and have a different font for unknown
entity, and in practice I suppose it is likely that you'd only start
entering signatures etc when the types and classes have already been
defined.
BTW this also assumes tycons and classcons share the same namespace. If this
were changed in future, then it would no longer be able to determine the
type/class distinction just by the id (but of course would eventually be
known after the = but this is too late for providing syntax help while
editing the context itself).
Thanks for the idea of making parens optional. I intend to try this as the
editor could still save/load files in normal H98 syntax (with parens) yet
allow them to be displayed/edited without for added user convenience... :-)
Regards, Brian.
--
Logic empowers us and Love gives us purpose.
Yet still phantoms restless for eras long past,
congealed in the present in unthought forms,
strive mightily unseen to destroy us.
http://www.metamilk.com
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[Haskell-cafe] Fran - Functional Reactive Animation
Title: Fran - Functional Reactive Animation Fran is a Haskell library (or embedded language) for interactive animations with 2D and 3D graphics and sound. See http://www.conal.net/fran/ and http://research.microsoft.com/research/downloads/download.aspx?FUID=c9eff407-ce59-4a2a-90cb-de099a9bacbd I would like to use Fran as a rapid prototyping environment for animations, but it appears to be broken under WinHugs. I'm looking for someone with much better Haskell prowess than myself who might be able resurrect Fran under WinHugs. Unfortunately I can only offer my gratitude in return. It's a long shot, I know. Kind regards, Neil Higgins Snr Strategic Planning Engineer ENERGEX Em: [EMAIL PROTECTED] Ph: 3407 4800 Fx: 3407 4832 * This email message (including any file attachments transmitted with it) is for the sole use of the intended recipient(s) and may contain confidential and legally privileged information. Any unauthorised review, use, alteration, disclosure or distribution of this email (including any attachments) by an unintended recipient is prohibited. If you have received this email in error, please notify the sender by return email and destroy all copies of the original message. Any confidential or legal professional privilege is not waived or lost by any mistaken delivery of the email. ENERGEX accepts no responsibility for the content of any email which is sent by an employee which is of a personal nature. Sender Details: ENERGEX GPO Box 1461 Brisbane QLD Australia 4001 +61 7 3407 4000 http://www.energex.com.au ENERGEX policy is to not send unsolicited electronic messages. Suspected breaches of this policy can be reported by replying to this message including the original message and the word "UNSUBSCRIBE" in the subject. * ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fran - Functional Reactive Animation
I think this works: http://haskell.org/edsl/pansharp.html Jared. On 8/23/06, HIGGINS Neil (ENERGEX) [EMAIL PROTECTED] wrote: Fran is a Haskell library (or embedded language) for interactive animations with 2D and 3D graphics and sound. See http://www.conal.net/fran/ and http://research.microsoft.com/research/downloads/download.aspx?FUID=c9eff407-ce59-4a2a-90cb-de099a9bacbd I would like to use Fran as a rapid prototyping environment for animations, but it appears to be broken under WinHugs. I'm looking for someone with much better Haskell prowess than myself who might be able resurrect Fran under WinHugs. Unfortunately I can only offer my gratitude in return. It's a long shot, I know. Kind regards, Neil Higgins Snr Strategic Planning Engineer ENERGEX Em: [EMAIL PROTECTED] Ph: 3407 4800 Fx: 3407 4832 * This email message (including any file attachments transmitted with it) is for the sole use of the intended recipient(s) and may contain confidential and legally privileged information. Any unauthorised review, use, alteration, disclosure or distribution of this email (including any attachments) by an unintended recipient is prohibited. If you have received this email in error, please notify the sender by return email and destroy all copies of the original message. Any confidential or legal professional privilege is not waived or lost by any mistaken delivery of the email. ENERGEX accepts no responsibility for the content of any email which is sent by an employee which is of a personal nature. Sender Details: ENERGEX GPO Box 1461 Brisbane QLD Australia 4001 +61 7 3407 4000 http://www.energex.com.au ENERGEX policy is to not send unsolicited electronic messages. Suspected breaches of this policy can be reported by replying to this message including the original message and the word UNSUBSCRIBE in the subject. * ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal question, adding data files
On Wed, Aug 23, 2006 at 11:36:00PM +0100, Neil Mitchell wrote: Hi The field you want is data-files, documented in section 2.1.1 of the Cabal User's Guide. That looks perfect. Is there any reason that Alex doesn't use this? I was trying to learn by example. Perhaps because Alex predates the data-files field; data-files was only introduced in Cabal 1.1.4. Hence you might want to also put the following at the top of your .cabal file: Cabal-Version: = 1.1.4 cheers, Conrad. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
