Re: How to best add logging/debugging code?
Ben Escoto wrote:
Hi all, does anyone have any tips on how to insert debugging or
logging statements through a program? Here are two possibilities:
another thing I found quite useful is
to add a component { .. , info :: Doc } to my data types,
and then set its value at each function call:
f x y = ( ... ) { info = parens $ fsep [ text f, info x, info y ] }
( I figure this is sort of part of what
some tools can do automatically? )
that way you always know who built what.
and it's cheap - if you don't use this information,
then it's never created (due to laziness).
best regards,
--
-- Johannes Waldmann, Tel/Fax: (0341) 3076 6479 / 6480 --
-- http://www.imn.htwk-leipzig.de/~waldmann/ -
___
Haskell mailing list
[EMAIL PROTECTED]
http://www.haskell.org/mailman/listinfo/haskell
Re: How to best add logging/debugging code?
Johannes Waldmann [EMAIL PROTECTED] writes:
f x y = ( ... ) { info = parens $ fsep [ text f, info x, info y ] }
Cool!
that way you always know who built what.
and it's cheap - if you don't use this information,
then it's never created (due to laziness).
Uh..is that really true? I would think it would keep a lot of data
from being garbage collected?
-kzm
--
If I haven't seen further, it is by standing in the footprints of giants
___
Haskell mailing list
[EMAIL PROTECTED]
http://www.haskell.org/mailman/listinfo/haskell
Re: Implementation of while loop
While while can be implemented in haskell, I would strongly suggest you look at using the many higher-order functions available (foldl/foldr, map, filter, etc.) - they're much more in line with the spirit of the language, and will lend themselves to much clearer expressions once you get the hang of them. What sort of thing do you want to do in your while loop? Is it a pure processing function, or an IO-related one? Abe [EMAIL PROTECTED] writes: Hi,does any one knows how to implement while-do loop or nested while-do loop? I'm in a situation that I need to implement nested while do loop with some if- then-else condition in my code,but I have no idea about it.Thanks. Ray This mail sent through www.mywaterloo.ca ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
ANN: H98 FFI Addendum 1.0, Release Candidate 16
Dear Haskell Folks, Release Candidate 16 of the H98 FFI Addendum 1.0 is now available from http://www.cse.unsw.edu.au/~chak/haskell/ffi/ Since the last version of the Addendum announced on [EMAIL PROTECTED], namely RC12, the FFI Task Force decided on a slight generalisation of the interface to finalizers as well as the addition of some support for string marshalling for characters sets beyond ASCII. A detailed change log is at the end of this message. I'd like to propose RC16 as the final form of Version 1.0 of the FFI Addendum. If you find any problems with this version, please raise them within the next two weeks. Cheers, Manuel -=- Changes since RC15: * 6.3: Footnote regarding __STDC_ISO_10646__ added to text introducing `CWString'. Changes since RC14: * 6.2: CWChar - CWchar * 6.3: - CWChar - CWchar - Stated explicitly that memory allocated by `newCString' and friends can be deallocated by `MarshalAlloc.free' - Improved documentation Changes since RC13: * 5.3: Fixed typo * 5.7: Fixed a mistake in the type of `peekByteOff' and `pokeByteOff' (the type variable constrained by `Storable' must be different from the parameter of the `Ptr') * 6.3: Improved documentation Changes since RC12: * Acks : Added John Meacham * 4.1.5: Bug fix courtesy of Wolfgang Thaller * 5.5 : Added `FinalizerEnvPtr', `newForeignPtrEnv', and `addForeignPtrFinalizerEnv' * 6.3 : Added John Meacham proposal for `wchar_t' support as well localised string marshalling; in particular, this adds `CWString' and `CWStringLen' as well as the `CWString' and the `CAString' family of marshalling routines. In addition, `charIsRepresentable' was added. ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Subsumption in partially ordered sets
I have a need for an algorithm to perform subsumption on partially ordered sets of values. That is, given a selection of values from a partially ordered set, remove all values from the collection that are less than some other member of the collection. Below is some code I have written, which works, but I'm not sure that it's especially efficient or elegant. Are there any published Haskell libraries that contain something like this? #g -- (The implementation here is based on values of type (Eq a) = [Maybe a], where the partial ordering is defined by function 'pcompare'. Function dropSubsumed (and helpers) is the subsumption calculation. testds1, testds2, testds3, testds4, testds5 are test cases, and all should be True.) [[ -- Type for result of partial order comparison (PNR is no-relationship) data PartOrdering = PLT | PEQ | PGT | PNR deriving (Eq, Show) -- Drop tuples from the supplied list that are subsumed by -- more specific ones. -- dropSubsumed :: (Eq a) = [[Maybe a]] - [[Maybe a]] dropSubsumed [] = [] dropSubsumed [a] = [a] dropSubsumed (a1:as) = dropSubsumed1 a1 as dropSubsumed1 a1 [] = [a1] dropSubsumed1 a1 (a2:a2s) = case pcompare a1 a2 of PEQ - dropSubsumed1 a1 a2s PGT - dropSubsumed1 a1 a2s PLT - dropSubsumed1 a2 a2s PNR - dropSubsumed2 [] a1 $ dropSubsumed1 a2 a2s -- Merge new head element into list from which subsumed elements -- have already been removed. The extra (first) parameter is used -- to construct a result in which the order of remaining elements -- is preserved with respect to the original list. dropSubsumed2 a1s a [] = a : revConcat a1s [] dropSubsumed2 a1s a ar@(a2:a2s) = case pcompare a a2 of PEQ - a : revConcat a1s a2s PGT - a : revConcat a1s a2s PLT - revConcat a1s ar PNR - dropSubsumed2 (a2:a1s) a a2s revConcat :: [a] - [a] - [a] revConcat [] a2s = a2s revConcat (a1:a1s) a2s = revConcat a1s (a1:a2s) -- Perform subsumption calculation between a pair of tuples -- A tuple with more information subsumes a one with less but -- consistent information. -- pcompare :: (Eq a) = [Maybe a] - [Maybe a] - PartOrdering pcompare a1s a2s = pcompare1 a1s a2s PEQ pcompare1 [][]po = po pcompare1 (Just _:a1s) (Nothing:a2s) po = if (po == PEQ) || (po==PGT) then pcompare1 a1s a2s PGT else PNR pcompare1 (Nothing:a1s) (Just _:a2s) po = if (po == PEQ) || (po==PLT) then pcompare1 a1s a2s PLT else PNR pcompare1 (a1:a1s) (a2:a2s) po = if a1 == a2 then pcompare1 a1s a2s po else PNR pcompare1 __ _ = PNR testds1 = ds1a == ds1b ds1a = dropSubsumed [ [Just 'a',Just 'b',Just 'c'] , [Just 'a',Just 'b',Nothing ] , [Just 'a',Nothing ,Just 'c'] , [Just 'a',Nothing ,Nothing ] , [Nothing ,Just 'b',Just 'c'] , [Nothing ,Just 'b',Nothing ] , [Nothing ,Nothing ,Just 'c'] , [Nothing ,Nothing ,Nothing ] ] ds1b = [ [Just 'a',Just 'b',Just 'c'] ] testds2 = ds2a == ds2b ds2a = dropSubsumed [ [Just 'a',Just 'b',Nothing ] , [Just 'a',Nothing ,Just 'c'] , [Just 'a',Nothing ,Nothing ] , [Nothing ,Just 'b',Just 'c'] , [Nothing ,Just 'b',Nothing ] , [Nothing ,Nothing ,Just 'c'] , [Nothing ,Nothing ,Nothing ] ] ds2b = [ [Just 'a',Just 'b',Nothing ] , [Just 'a',Nothing ,Just 'c'] , [Nothing ,Just 'b',Just 'c'] ] testds3 = ds3a == ds3b ds3a = dropSubsumed [ [Just a1,Just b1,Just c1] , [Just a2,Just b2,Nothing ] , [Just a3,Nothing ,Just c3] , [Just a4,Nothing ,Nothing ] , [Nothing ,Just b5,Just c5] , [Nothing ,Just b6,Nothing ] , [Nothing ,Nothing ,Just c7] , [Nothing ,Nothing ,Nothing ] ] ds3b = [ [Just a1,Just b1,Just c1] , [Just a2,Just b2,Nothing ] , [Just a3,Nothing ,Just c3] , [Just a4,Nothing ,Nothing ] , [Nothing ,Just b5,Just c5] , [Nothing ,Just b6,Nothing ] , [Nothing ,Nothing ,Just c7] ] testds4 = ds4a == ds4b ds4a = dropSubsumed [ [Just 1, Just 1 ] , [Just 2, Nothing] , [Nothing,Just 3 ] , [Nothing,Nothing] ] ds4b = [ [Just 1, Just 1 ] , [Just 2, Nothing] , [Nothing,Just 3 ] ] -- Check handling of equal values testds5 = ds5a == ds5b ds5a = dropSubsumed [ [Just 1, Just 1 ] , [Just 2, Nothing] , [Nothing,Just 3 ] , [Nothing,Nothing] , [Just 1, Just 1 ] , [Just 2, Nothing] , [Nothing,Just 3 ] ] ds5b = [ [Just 1, Just 1 ] , [Just 2, Nothing] , [Nothing,Just 3 ] ] ]] ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Subsumption in partially ordered sets
Graham Klyne writes: : | Below is some code I have written, which works, but I'm not sure | that it's especially efficient or elegant. Are there any published | Haskell libraries that contain something like this? Hi. Partially ordered sets are in cahoots with lattices, so you may be interested in http://www.cse.ogi.edu/~mpj/pubs/lattices.html . And here's some off-the-cuff feedback... How about using Maybe Ordering, instead of a new data type? (As in http://www.mail-archive.com/[EMAIL PROTECTED]/msg05635.html) Instead of hard-wiring Maybe into the element type in dropSubsumed, how about passing in a partial comparison function? dropSubsumedBy :: (a - a - Maybe Ordering) - [a] - [a] - Tom ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Subsumption in partially ordered sets
I have a need for an algorithm to perform subsumption on partially ordered sets of values. That is, given a selection of values from a partially ordered set, remove all values from the collection that are less than some other member of the collection. That is, you want the maxima, right? The following seems to work, though I don't know how efficient it is. maxima :: (Eq a) = [[Maybe a]] - [[Maybe a]] maxima es = maxima' [] es where maxima' ms [] = ms maxima' ms (e:es) = maxima' (add ms e) es add [] e = [e] add (m:ms) e = case pcompare m e of PNR - m:(add ms e) PGT - m:ms PLT - add ms e PEQ - m:ms Cheers Robert ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
There is flexible exception handling in Haskell?
Hi all. I am porting to Haskell a small zlib-based library for .zip files (I have not seen any released package for it, although it should very useful). The matters come when I try to address exceptional conditions: all the library functions return a integer code with OK/SOMEERROR meaning. The most natural way to carry the exceptional situations should be raise IO exceptions, but here comes the problem: how can I define new Exception codes, instead of raising userError all the time? I think it makes sense for a library to raise specialized exceptions, instead of userErrors. There is such a mechanism? Can someone help? Thanks. - Este mensaje lo ha enviado un Alumno de la Universidad de Malaga. http://www.alumnos.uma.es/ ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
There is flexible exception handling in Haskell?
Hi all. I am porting to Haskell a small zlib-based library for .zip files (I have not seen any released package for it, although it should very useful). The matters come when I try to address exceptional conditions: all the library functions return a integer code with OK/SOMEERROR meaning. The most natural way to carry the exceptional situations should be raise IO exceptions, but here comes the problem: how can I define new Exception codes, instead of raising userError all the time? I think it makes sense for a library to raise specialized exceptions, instead of userErrors. There is such a mechanism? Can someone help? Thanks. - Este mensaje lo ha enviado un Alumno de la Universidad de Malaga. http://www.alumnos.uma.es/ ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: There is flexible exception handling in Haskell?
Hi all. I am porting to Haskell a small zlib-based library for .zip files (I have not seen any released package for it, although it should very useful). The matters come when I try to address exceptional conditions: all the library functions return a integer code with OK/SOMEERROR meaning. The most natural way to carry the exceptional situations should be raise IO exceptions, Sometimes you can just encode your exceptional values in some type. It tends to be more declarative than throwing/catching exceptions: data Result = Ok Int | ThisError | ThatError String | SomeError Int ... And you library functions can be: fun :: Foo - Bar - IO Result drop the IO type if you don't need it. but here comes the problem: how can I define new Exception codes, instead of raising userError all the time? I think it makes sense for a library to raise specialized exceptions, instead of userErrors. There is such a mechanism? Can someone help? If the encoding doesn't somehow suit your needs then you could try GHC's exception extensions, which provide a much richer exception facility than plain Haskell 98 Have a look at the module Control.Exception in the user docs. I think that very modern versions of Hugs support some of this extension too. Cheers, Bernie. ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
