[Haskell-cafe] Re: Closest analog to popen()
Dimitry Golubovsky writes: Does there exist any analog of popen in the standard Haskell libraries? Maybe System.Process.runInteractiveCommand is what you need? http://haskell.org/ghc/docs/latest/html/libraries/base/System.Process.html Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Binary file r/w example
Ptr is defined in the FFI, which is documented here: http://www.cse.unsw.edu.au/~chak/haskell/ffi/ and also in the GHC documentation: http://www.haskell.org/ghc/docs/latest/html/libraries/base/Foreign.Ptr.html I haven't done much binary IO, so I'll let someone else handle that, but there are some libraries for doing binary IO in Haskell linked from here: http://www.haskell.org/hawiki/BinaryIo - Cale On 4/13/05, Bo Herlin [EMAIL PROTECTED] wrote: Yes, I am, and the IOExtension module IS one of my problems. The other problem is that I am interested in this Ptr thing, and I havent seen any examples in using it, and is seems like Ptr is not in any of my Haskell-books or in any of the tutorials that I have found. Henning Thielemann wrote: On Wed, 13 Apr 2005, Bo Herlin wrote: Hi, does anyone have a small but complete example on how to read a (portion of) a binary file, like r/w the header of a Midi-file? It seems like readBinaryFile (ans writeBinaryFile) is deprecated and I should use hGetBuf (and hPutBuf), but what is this Ptr thing? How would I implement readBinaryFile using hGetBuf? Are you aware of Haskore (www.haskell.org/haskore and cvs.haskell.org/darcs/haskore) which provides a MidiFile reader and writer? It has no good solution for reading and writing binary files, but uses a platform dependent IOExtension module. :-( ___ 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] Installing and running QuickCheck
Hi Daniel, Yes, importing Data.Char worked, but revealed other problems. Now I get the following. ERROR C:\Program Files\Hugs98\libraries\QuickCheck.hs:161 - Undefined variable fromInt Monad This, however, I have seen before, and it has to do with different versions of Prelude, where fromInt was removed and fromInteger put in. From hugs-bugs, we find that we need to just change fromInt to fromInteger on the appropriate line. http://www.haskell.org/pipermail/hugs-bugs/2005-January/001537.html So, starting with line 160 of QuickCheck.hs should read: instance Arbitrary Integer where arbitrary = sized $ \n - choose (-fromIntegral n,fromIntegral n) coarbitrary n = variant (fromInteger (if n = 0 then 2*n else 2*(-n) + 1)) And with these two changes, QuickCheck compiles. Now I have to see how it works. Thanks, Adam Quoting Daniel Fischer [EMAIL PROTECTED]: Hm, no instance Arbitrary Char is provided in the QuickCheck modules that came with my hugs or ghc. Probably the author just forgot to import Data.Char. Try inserting that in QuickCheck.hs. Hope that works, Daniel This message was sent using IMP, the Internet Messaging Program. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [Q] A typing problem
Hi ! I'm trying to write a function that combines folding and mapping. This function would take two arguments (a folding function and a mapping function), and would return a function of one argument (a list of 'a''s) returning a 'a'. The idea is to write something like sumsquare = foldmap (+) square Here's what I write: foldmap :: (c - c - c) - (c - c) - (c - c - c) foldmap f m = foldr1 f (map m) But this gives a typing error: ERROR src/ssq4.hs:2 - Type error in application *** Expression : foldr1 f (map m) *** Term : map m *** Type : [b] - [b] *** Does not match : [a] What can I do to get what I want ? Thanks. -- Didier Verna, [EMAIL PROTECTED], http://www.lrde.epita.fr/~didier EPITA / LRDE, 14-16 rue Voltaire Tel.+33 (1) 44 08 01 85 94276 Le Kremlin-Bicêtre, France Fax.+33 (1) 53 14 59 22 [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Q] A typing problem
On Wed, 13 Apr 2005, Didier Verna wrote: I'm trying to write a function that combines folding and mapping. This function would take two arguments (a folding function and a mapping function), and would return a function of one argument (a list of 'a''s) returning a 'a'. The idea is to write something like sumsquare = foldmap (+) square Here's what I write: foldmap :: (c - c - c) - (c - c) - (c - c - c) foldmap f m = foldr1 f (map m) Do you mean foldmap :: (b - b - b) - (a - b) - [a] - b foldmap f m = foldr1 f . map m ? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] foldr1 min [(maxBound::Int)%1,1 % 2]
Hi How come foldr1 min [(maxBound::Int) % 1,1 % 2] 2147483647 % 1 but foldr1 min [2147483647 % 1,1 % 2] 1 % 2 Why??? /Bo Herlin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] foldr1 min [(maxBound::Int)%1,1 % 2]
On Wed, 13 Apr 2005, Bo Herlin wrote: Hi How come foldr1 min [(maxBound::Int) % 1,1 % 2] 2147483647 % 1 I guess that foldr1 min == minimum but foldr1 min [2147483647 % 1,1 % 2] 1 % 2 Why??? The first one certainly causes an overflow with machine word Ints whereas 2147483647 is an Integer and thus all other numbers are interpreted as Integers. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] foldr1 min [(maxBound::Int)%1,1 % 2]
Hmm... let a = (maxBound :: Int)%1 in 1 a a 1/2 == True From the Ord instance for Ratio a (x:%y) (x':%y') = x * y' x' * y So the comparison for 1 a looks like 1 * 1 (maxBound :: Int) * 1 which is true. And the comparison for a 1/2 looks like (maxBound :: Int) * 2 1 * 1 == -2 1 which is again true! If you want well-behaved rationals, I suppose you have to use Ratio Integer. Hope this helps, - Cale On 4/13/05, Bo Herlin [EMAIL PROTECTED] wrote: Hi How come foldr1 min [(maxBound::Int) % 1,1 % 2] 2147483647 % 1 but foldr1 min [2147483647 % 1,1 % 2] 1 % 2 Why??? /Bo Herlin ___ 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] [Q] A typing problem
I'm trying to write a function that combines folding and mapping a map is a fold:) idList = foldr (:) [] map f = foldr ((:) . f) [] foldmap :: (b - b - b) - (a - b) - [a] - b foldmap f m = foldr1 f . map m alternatively, and dealing with empty lists as well foldmap op n f = foldr (op . f) n cheers, claus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Passing Constructors as arguments
I am learning Haskell and have set a small exercise for myself on a frames and slots program. Would appreciate some help on how to pass constructors of data structures as arguments to a function. Thanks, -- Ralph __ A Frames test module Frames where Define frame slots: type FirstName = String -- first name type LastName = String -- last name type Organization = String type Email = String type WorkPhone = String type CellPhone = String type TelephoneNumber = String Define slots for a contact data ContactProperty = FN FirstName | LN LastName | OR Organization | EM Email | WP TelephoneNumber | MP TelephoneNumber deriving (Show, Eq) data Contact = Contact [ContactProperty] deriving (Show, Eq) type Contacts = [ Contact] Now I need a way to extract properties from the frame. Start by testing pattern matching without using parameters. Then I need to find out how to pass a constructor as a parameter. getProperty:: [ContactProperty] - FirstName getProperty ((FN fn):_) = fn getProperty (_:xs) = getProperty xs getProperty [] = "unknown" firstName:: Contact - FirstName firstName (Contact cpl) = getProperty cpl Define Contacts c1::Contacts c1 = [ ( Contact [(FN "Ralph"),(LN "Hodgson"),(OR "TopQuadrant"),(EM "[EMAIL PROTECTED]")]), ( Contact [(FN "Mills"),(LN "Davis"),(EM "[EMAIL PROTECTED]")])] Tests t1=firstName $ head c1 -- should be "Ralph" t2=firstName $ last c1 -- should be "Mills" ___ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] foldr1 min [(maxBound::Int)%1,1 % 2]
Hmm, too simple :-P ...Thanks Henning Thielemann wrote: On Wed, 13 Apr 2005, Bo Herlin wrote: Hi How come foldr1 min [(maxBound::Int) % 1,1 % 2] 2147483647 % 1 I guess that foldr1 min == minimum but foldr1 min [2147483647 % 1,1 % 2] 1 % 2 Why??? The first one certainly causes an overflow with machine word Ints whereas 2147483647 is an Integer and thus all other numbers are interpreted as Integers. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] foldr1 min [(maxBound::Int)%1,1 % 2]
Yep, got it, Thanks! Cale Gibbard wrote: Hmm... let a = (maxBound :: Int)%1 in 1 a a 1/2 == True From the Ord instance for Ratio a (x:%y) (x':%y') = x * y' x' * y So the comparison for 1 a looks like 1 * 1 (maxBound :: Int) * 1 which is true. And the comparison for a 1/2 looks like (maxBound :: Int) * 2 1 * 1 == -2 1 which is again true! If you want well-behaved rationals, I suppose you have to use Ratio Integer. Hope this helps, - Cale On 4/13/05, Bo Herlin [EMAIL PROTECTED] wrote: Hi How come foldr1 min [(maxBound::Int) % 1,1 % 2] 2147483647 % 1 but foldr1 min [2147483647 % 1,1 % 2] 1 % 2 Why??? /Bo Herlin ___ 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] Passing Constructors as arguments
Am Mittwoch, 13. April 2005 15:43 schrieb Ralph Hodgson:
I am learning Haskell and have set a small exercise for myself on a
frames and slots program.
Would appreciate some help on how to pass constructors of data
structures as arguments to a function.
Thanks,
-- Ralph
snip
Now I need a way to extract properties from the frame. Start by testing
pattern matching
without using parameters. Then I need to find out how to pass a
constructor as a parameter.
Your code works fine.
I'm not sure, what your problem is.
Given type-correctness, data constructors can be passed as arguments to
functions like any other function. Probably that's not your question,
however.
As a wild guess, maybe you should use labelled records,
data Contact = Contact
{ firstName :: FirstName
, lastName :: LastName
, ...
}
and you have your selector-functions.
And it's possible to define partial contacts as
me = Contact{firstName=Daniel, lastName=Fischer}
-- just don't ask for my phone-number or anything else which is undefined.
If I'm far off, state your problem more precisely.
getProperty:: [ContactProperty] - FirstName
getProperty ((FN fn):_) = fn
getProperty (_:xs) = getProperty xs
getProperty [] = unknown
firstName:: Contact - FirstName
firstName (Contact cpl) = getProperty cpl
Cheers,
Daniel
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Q] A typing problem
Henning Thielemann [EMAIL PROTECTED] wrote: Do you mean foldmap :: (b - b - b) - (a - b) - [a] - b foldmap f m = foldr1 f . map m But of course ! Thanks :-) -- Didier Verna, [EMAIL PROTECTED], http://www.lrde.epita.fr/~didier EPITA / LRDE, 14-16 rue Voltaire Tel.+33 (1) 44 08 01 85 94276 Le Kremlin-Bicêtre, France Fax.+33 (1) 53 14 59 22 [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Passing Constructors as arguments
I don't really understand what you want to achieve : constructors are functions, thus first class objects ... I suppose you want a destructor, ie a function extracting the first name from a property for example. You may want to have a look there : http://haskell.org/hawiki/DecoratingStructures Pierre Ralph Hodgson a écrit : I am learning Haskell and have set a small exercise for myself on a frames and slots program. Would appreciate some help on how to pass constructors of data structures as arguments to a function. Thanks, -- Ralph __ A Frames test module Frames where Define frame slots: type FirstName = String -- first name type LastName= String -- last name type Organization = String type Email = String type WorkPhone = String type CellPhone = String type TelephoneNumber = String Define slots for a contact data ContactProperty = FN FirstName | LN LastName | OR Organization | EM Email | WP TelephoneNumber | MP TelephoneNumber deriving (Show, Eq) data Contact = Contact [ContactProperty] deriving (Show, Eq) type Contacts = [ Contact] Now I need a way to extract properties from the frame. Start by testing pattern matching without using parameters. Then I need to find out how to pass a constructor as a parameter. getProperty:: [ContactProperty] - FirstName getProperty ((FN fn):_) = fn getProperty (_:xs) = getProperty xs getProperty [] = unknown firstName:: Contact - FirstNamen firstName (Contact cpl) = getProperty cpl Define Contacts c1::Contacts c1 = [ ( Contact [(FN Ralph),(LN Hodgson),(OR TopQuadrant),(EM [EMAIL PROTECTED])]), ( Contact [(FN Mills),(LN Davis),(EM [EMAIL PROTECTED])])] Tests t1=firstName $ head c1 -- should be Ralph t2=firstName $ last c1 -- should be Mills ___ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Pierre Barbier de Reuille INRA - UMR Cirad/Inra/Cnrs/Univ.MontpellierII AMAP Botanique et Bio-informatique de l'Architecture des Plantes TA40/PSII, Boulevard de la Lironde 34398 MONTPELLIER CEDEX 5, France tel : (33) 4 67 61 65 77fax : (33) 4 67 61 56 68 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Passing Constructors as arguments
Thanks for your help Daniel - I am clarifying my message
Daniel Fischer wrote:
Am Mittwoch, 13. April 2005 15:43 schrieb Ralph Hodgson:
I am learning Haskell and have set a small exercise for myself on a
frames and slots program.
Would appreciate some help on how to pass constructors of data
structures as arguments to a function.
Thanks,
-- Ralph
snip
Now I need a way to extract properties from the frame. Start by testing
pattern matching
without using parameters. Then I need to find out how to pass a
constructor as a parameter.
Your code works fine.
I'm not sure, what your problem is.
Given type-correctness, data constructors can be passed as arguments to
functions like any other function. Probably that's not your question,
however.
I would like to see an example of passing constructors as arguments. I
am still getting familiar with constructs like:
getProperty ( a - b) - [ContactProperty] - b
I am not sure how to test the Constructor passed as the argument. Do I
say the following:
getProperty c ((c v:_) = v
getProperty c ((_:xs) = getProperty c xs
..
I have tried doing this but GHC gives me parse errors. There is Haskell
syntax that I don't know yet that I need to learn.
As a wild guess, maybe you should use labelled records,
data Contact = Contact
{ firstName :: FirstName
, lastName :: LastName
, ...
}
and you have your selector-functions.
thanks - very useful
And it's possible to define partial contacts as
me = Contact{firstName=Daniel, lastName=Fischer}
-- just don't ask for my phone-number or anything else which is undefined.
If I'm far off, state your problem more precisely.
getProperty:: [ContactProperty] - FirstName
getProperty ((FN fn):_) = fn
getProperty (_:xs) = getProperty xs
getProperty [] = unknown
firstName:: Contact - FirstName
firstName (Contact cpl) = getProperty cpl
Cheers,
Daniel
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Passing Constructors as arguments
Am Mittwoch, 13. April 2005 17:14 schrieben Sie:
Thanks for your help Daniel - I am clarifying my message
I would like to see an example of passing constructors as arguments. I
am still getting familiar with constructs like:
getProperty ( a - b) - [ContactProperty] - b
I am not sure how to test the Constructor passed as the argument. Do I
This isn't an argument, by the way, it's a parameter.
say the following:
getProperty c ((c v:_) = v
getProperty c ((_:xs) = getProperty c xs
You can't do it thus, a variable-pattern like c may only appear once in a
function definition and c v isn't a legal pattern, so may not appear on the
lhs of the definition. Neither may an incompletely applied constructor:
Hugs mode: Restart with command line option +98 for Haskell 98 mode
ERROR ./Ini.hs:29 - Constructor Left must have exactly 1 argument in
pattern
The offending line is
humm Left = LT
You can achieve your goal with dummy values:
getProperty c@(FN d) (x:xs) = case x of
FN fn - fn
_ - getProperty c xs
getProperty c@(LN d) (x:xs) = case x of
LN ln - ln
_ - getProperty c xs
...
and then call
getProperty (FN undefined) list.
This isn't very nice, though. I'd rather do it (if labelled records aren't the
thing to do) using Maybe types:
firstName :: ContactProperty - Maybe FirstName
firstName (FN fn) = Just fn
firstName _ = Nothing
and so on, then (this depends on all properties being represented by a String,
if different types were involved, it'd be more complicated)
getProperty :: (ContactProperty - Maybe String) - [ContactProperty]
- String
getProperty f xs = case catMaybes $ map f xs of
[] - unknown
(p:ps) - p
However, this isn't nice either.
..
I have tried doing this but GHC gives me parse errors. There is Haskell
syntax that I don't know yet that I need to learn.
Quite natural, I strongly recommend reading the 'Gentle Introduction to
Haskell' and every now and then looking whether you already know enough
Haskell to profit by reading the report. The sections on pattern matching
have valuable information on the problem at hand.
As a wild guess, maybe you should use labelled records,
data Contact = Contact
{ firstName :: FirstName
, lastName :: LastName
, ...
}
and you have your selector-functions.
thanks - very useful
Nice to read that :-)
Cheers,
Daniel
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Closest analog to popen()
Peter Simons wrote: Dimitry Golubovsky writes: Does there exist any analog of popen in the standard Haskell libraries? Maybe System.Process.runInteractiveCommand is what you need? http://haskell.org/ghc/docs/latest/html/libraries/base/System.Process.html Is this available only in 6.4? In 6.2.2 I've got only System.Posix.Process, and this is just binding to Unix functions dealing with processes. Thanks for pointing me out. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
