- Haskell-Cafe - Haskell.org

Problems with Validate from HaXML
by Samuel Silva 12 Jun '08

12 Jun '08

Hello I'm working with large DTDs from http://www.recordare.com/dtds/, particulary partwise.dtd and timewise.dtd. I check these DTDs with some tools, like Altova XML Spy and Microsoft Visual Studio, and DTDs are valid. However Validate tool from HaXML doesn't validate same DTDs. Result from Validate is: $ Validate partwise.dtd Validate: In a sequence: in content spec of ELEMENT decl: note When looking for a non-empty sequence with separators: Expected % but found | in file note.mod at line 51 col 45 used by file partwise.dtd at line 120 col 1 when looking for a content particle when looking for a content particle Problematic definition is in "note.mod" file, presented below: <!ELEMENT note (((grace, %full-note;, (tie, tie?)?) | (cue, %full-note;, duration) | (%full-note;, duration, (tie, tie?)?)), instrument?, %editorial-voice;, type?, dot*, accidental?, time-modification?, stem?, notehead?, staff?, beam*, notations*, lyric*)> I'm trying using DtdToHaskell tool from HaXML to build parser from MusicXML to Haskell types. There are other ways to build XML parser using HaXML? I'm already using HaXML, with HaXML combinators, to write MusicXML. Thanks. -- Don't hug that, Hugs ME! Samuel Silva

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Simple list processing
by Andrew Coppin 12 Jun '08

12 Jun '08

OK, so this is a fairly basic question about list processing. Several times now, I have found myself wanting to process a list to produce a new list. However, the way later elements are processed depends on what the earlier elements are - in other words, this isn't a simple "map". What is the best way to handle this? According to the theory, anything that consumes a list and produces a value is some kind of fold. [Assuming it traverses the list in a sensible order!] So it looks like you could implement this as a fold. But should that be a LEFT-fold or a RIGHT-fold? (I always get confused between the two!) Actually, anything that takes a value and processes it repeatedly to produce a list is technically an unfold. [Again assuming a sensible processing order.] So it looks like this function could also be an UNfold. As in, you take a list as input, and keep unfolding until that list becomes empty. So it looks like this can be implemented as a fold or an unfold. But neither way looks especially easy. Both of these patterns seem to be more general than necessary; I only want to take 1 element of input and produce 1 element of output, but keeping track of a running state. I guess I could use some sort of state monad and make the whole thing monadic - but that again is overkill for what I'm trying to do. Any hints here?

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appending an element to a list
by Adrian Neumann 12 Jun '08

12 Jun '08

Hello, I was wondering how expensive appending something to a list really is. Say I write I'd say "longList ++ [5]" stays unevaluated until I consumed the whole list and then appending should go in O(1). Similarly when concatenating two lists. Is that true, or am I missing something? Adrian

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ANN: ieee-0.2
by Patrick Perry 12 Jun '08

12 Jun '08

ieee is a library that provides approximate comparison of floating point numbers based, NaN-aware minimum and maximum, and a type class for approximate comparisons. This version fixes a bug in the comparison implementation for Maybe. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ieee

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ANN: blas-0.4.1
by Patrick Perry 12 Jun '08

12 Jun '08

There were a few hiccups in the release of 0.4, so this version is to make installation go a little smoother for people. There are now installation instructions (the INSTALL file) and configuration settings for some common CBLAS (ATLAS, MKL, vecLib, GSL). The default is now to assume that ATLAS is installed, so hopefully most people won't have to fuss too much with this. Alberto Ruiz reported two small issues with precision in the unit tests, and those have now been fixed. Patrick

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Haskell Weekly News: Issue 72 - June 11, 2008
by Brent Yorgey 11 Jun '08

11 Jun '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080611 Issue 72 - June 11, 2008 --------------------------------------------------------------------------- Welcome to issue 72 of HWN, a newsletter covering developments in the [1]Haskell community. Greetings, Haskellites! As many of you have already heard, Don Stewart has passed on the editorship of the HWN to me (Brent Yorgey). I'd like to thank Don and John Goerzen for their great work putting it together in the past, and I'm excited to make the HWN once again into a reliable, useful compendium of happenings in the Haskell community. You can expect to see a few changes---for example, hackage uploads will no longer be listed in the HWN (unless they are announced on the haskell or haskell-cafe mailing lists), since you can now see a dynamically updated list on the front page of the Haskell wiki. This edition includes all the announcements going back to Issue 71, but only some of the blog posts, since I couldn't find a way to get old feed data from Planet Haskell. Hopefully next week things will settle down to something more normal(ish) and I can begin tinkering with the format. Feel free to send suggestions and/or stories for inclusion to me, byorgey at gmail dot com. Enjoy---'Putting the W back in HWN!' Announcements hfann. Olivier Boudry [2]announced the first release of the [3]hfann module, an interface to the [4]'Fast Artificial Neural Network (FANN)' library. funsat. Denis Bueno [5]announced a release of [6]funsat, a modern, DPLL-style SAT solver written in Haskell. Funsat solves formulas in conjunctive normal form and produces a total variable assignment for satisfiable problems. DEFUN08: Call for talks and tutorials. Matthew Fluet [7]announced the final call for talks and tutorials at [8]DEFUN 2008, to be held in conjunction with [9]ICFP. Cabal-1.4 Release Candidate. Duncan Coutts [10]announced the second release candidate for [11]Cabal-1.4. Programmer's Minesweeper. Bertram Felgenhauer [12]announced a Haskell implementation of [13]Programmer's Minesweeper, which allows programmers to implement minesweeper strategies and run them. hackage RSS feed. Don Stewart [14]announced a new [15]RSS feed for the most recently uploaded packages on [16]Hackage. BLAS bindings. Patrick Perry [17]announced a set of bindings for the [18]BLAS linear algebra library. Xen Control bindings. Thomas DuBuisson [19]announced the [20]hsXenCtrl package, with FFI bindings to [21]Xen. bloomfilter. Bryan O'Sullivan [22]announced the availability of a fast Bloom filter library for Haskell. A Bloom filter is a probabilistic data structure that provides a fast set membership querying capability. It does not give false negatives, but has a tunable false positive rate. HCAR. Janis Voigtlaender [23]announced the 14th edition of the [24]Haskell Community and Activities Report (HCAR). HSmugMug. Daniel Patterson [25]announced [26]HSmugMug, a Haskell wrapper to the photo hosting site [27]SmugMug's API. LIPL. Sam Lee [28]announced the release of [29]LIPL, a tiny functional language implemented as a term project to learn Haskell. Glome 0.51. Jim Snow [30]announced version 0.51 of [31]glome, a raytracer written in Haskell. ChessLibrary. Andrew Wagner [32]announced the [33]ChessLibrary project, and mentioned that he is looking for an experienced haskeller to serve as a mentor for this project. xmonad-utils. Gwern Branwen [34]announced the upload to hackage of [35]xmonad-utils, a couple of small Xlib programs which might be useful for xmonad users. Roguestar. Christopher Lane Hinson [36]announced the release of [37]Roguestar 0.2, a science fiction themed roguelike (turn-based, chessboard-tiled, role playing) game written in Haskell. Streaming Component Combinators. Mario Blazevic [38]announced the 0.1 release of [39]Streaming Component Combinators in Haskell, based on earlier work done in [40]OmniMark. Twitter client. Chris Eidhof [41]announced a simple [42]terminal-based Twitter client. Monad.Reader call for copy. Wouter Swierstra [43]issued a call for copy for [44]The Monad.Reader. The submission deadline for Issue 11 is August 1. category-extras. Edward Kmett [45]announced a new release of the [46]category-extras package, involving all sorts of new categorical goodness. Session Types for Haskell. Matthew Sackman [47]announced the availability of [48]Session Types for Haskell. Session types are a means of describing communication between multiple threads, and statically verifying that the communication being performed is safe and conforms to the specification. Haddock 2.1.0. David Waern [49]announced the release of [50]Haddock 2.1.0. ReviewBoard. Adam Smyczek [51]announced the release of [52]Haskell bindings to [53]ReviewBoard, a development tool designed to monitor code changes and analyze dependencies. diagrams. Brent Yorgey [54]announced the initial release of [55]Graphics.Rendering.Diagrams, an embedded domain-specific language for creating simple pictures and diagrams, built on top of the Cairo vector graphics library. HXT. Uwe Schmidt [56]announced a new release of the [57]Haskell XML Toolbox. GSoC. Malcolm Wallace [58]announced the seven student projects chosen to be funded by the [59]Google Summer of Code. bytestring. Don Stewart [60]announced a new major release of [61]bytestring, the efficient string library for Haskell, suitable for high-performance scenarios. HXQ. Leonidas Fegaras [62]announced the release of [63]HXQ, an [64]XQuery compiler/interpreter for Haskell. Win32-notify. Niklas Broberg [65]announced the first release of [66]Win32-notify, an inotify-alike for Windows. cpuid. Martin Grabmueller [67]announced the new [68]cpuid package, which provides functionality for accessing information about the currently running IA-32 processor. Emping. Hans van Thiel [69]announced version 0.5 of the [70]Emping package, a utility which derives the shortest rules from a table of rules. datapacker. John Goerzen [71]announced the first release of [72]datapacker, a tool to pack files into a minimum number of CDs, DVDs, or any other arbitrary bin. darcswatch. Joachim Breitner [73]announced the release of [74]darcswatch, a tool for tracking darcs patches and repositories. Generic Haskell. Thomas van Noort [75]announced the fifth release of [76]Generic Haskell, an extension of Haskell that facilitates generic programming. drawingcombinators. Luke Palmer [77]announced the release of [78]graphics-drawingcombinators, a wrapper around OpenGL with a functional interface. The Monad.Reader. Wouter Swierstra [79]announced the publication of Issue 10 of [80]The Monad.Reader, a quarterly magazine about functional programming. Well-Typed LLP. Ian Lynagh [81]announced that he, Björn Bringert and Duncan Coutts have set up a Haskell consultancy company, [82]Well-Typed LLP. Their services include application development, library and tool maintenance, project advice, and training. hgdbmi. Evan Martin [83]announced the [84]hgdbmi package, which wraps the operations of attaching GDB to a process and parsing the GDB/MI output. xmonad. Don Stewart [85]announced the release of [86]xmonad version 0.7. Updates include improved integration with GNOME, more flexible "rules", various stability fixes, and of course, many new and interesting features in the extension library. Haskell Server Pages. Niklas Broberg [87]announced a new release of [88]Haskell Server Pages, a programming model for writing dynamic web pages in Haskell, both server-side and client-side. Network.MiniHTTP. Adam Langley [89]announced a release of [90]network-minihttp, a small bytestring HTTP library. Disciplined Disciple Compiler. Ben Lippmeier [91]announced the initial alpha release of the [92]Disciplined Disciple Compiler, an explicitly lazy dialect of Haskell. haskell-src-exts. Niklas Broberg [93]announced a new release for [94]haskell-src-exts, a package for handling and manipulating Haskell source code. omnicodec. Magnus Therning [95]announced the package [96]omnicodec, containing two command line utilities for encoding and decoding data. Blog noise [97]Haskell news from the [98]blogosphere. * [99]Christophe Poucet (vincenz): ICFP Contest 2008 * [100]Real-World Haskell: CUFP 2007 videos now easier to view * [101]Wrap-up: mergesort in haskell * [102]jbofihe and Haskell * [103]Writing a Regular Expression parser in Haskell: Part 3 * [104]Real World Haskell * [105]London Haskell Users Group: Next meeting: Paradise, a DSEL for derivatives pricing * [106]Christophe Poucet (vincenz): Lazy memoization * [107]Neil Mitchell: GSoC Hoogle: Week 2 * [108]Magnus Therning: Google Treasure Hunt primes question * [109]Roman Cheplyaka: Status report: week 2 * [110]Andy Gill: The unknown cost of dictionaries * [111]Edward Kmett: Zapping Adjunctions * [112]Edward Kmett: Representing Adjunctions * [113]Andy Gill: Performance problems with functional representation of derivatives * [114]Conal Elliott: Functional linear maps Quotes of the Week * roconnor: if you click your heels and say ``there is no binding like gtk2hs'' then dcoutts will appear and answer your question. * mauke: the first rule of fix club is "the first rule of fix club is "the first rule of fix club is... * oerjan: so does this mean that a comonad is like a wildlife preserve on an island in a sea of nuclear waste? * quicksilver: head-explosion is the solution, not the problem. * Botje: [on googling for polyvariadic typeclasses] OH GOD THE FIRST HIT IS OLEGS SITE! / *ahum* / I meant, "yay, reading material" * Baughn: From my point of view, anyone who understands everything ghc can do is /scary/. I'm sure that will change once I reach that level myself, but then again, there's also the possibility that I'll be in a permanent state of autophobia. * newsham: I think the problem with people asking homework questions in this channel is that the people in this channel don't have enough homework questions of their own to do. * quicksilver: *** quicksilver beats Deewiant with the i-will-not-use-fail-stick [Deewiant] quicksilver: I'm willing to accept a good alternative. [quicksilver] no. all you are permitted to accept is a beating. * mar77a: MONAD ARGHH GHGRHGH HGHRGHR RUN * Cale: Types are a bit like the nubs on lego bricks which provide structural integrity while suggesting how the bricks should fit together. * quicksilver: zip`ap`tail the aztec god of consecutive numbers About the Haskell Weekly News New editions are posted to [115]the Haskell mailing list as well as to [116]the Haskell Sequence and [117]Planet Haskell. [118]RSS is also available, and headlines appear on [119]haskell.org. Headlines are available as [120]PDF. To help create new editions of this newsletter, please see the [121]contributing information. Send stories to byorgey at gmail dot com. The darcs repository is available at darcs get [122]http://code.haskell.org/~byorgey/code/hwn/ References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41154 3. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hfann 4. http://leenissen.dk/fann/ 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41167 6. http://churn.ath.cx/funsat.html 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38392 8. http://www.deinprogramm.de/defun-2008/ 9. http://www.icfpconference.org/icfp2008/ 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41059 11. http://www.haskell.org/cabal/ 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40950 13. http://www.ccs.neu.edu/home/ramsdell/pgms/index.html 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41045 15. http://hackage.haskell.org/packages/archive/recent.rss 16. http://hackage.haskell.org/ 17. http://quantile95.com/?p=5 18. http://www.netlib.org/blas/ 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40790 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsXenCtrl 21. http://xen.org/ 22. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40745 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40703 24. http://www.haskell.org/communities/ 25. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40546 26. http://dbpatterson.com/articles/10 27. http://www.smugmug.com/ 28. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40500 29. http://www.lipl.googlepages.com/index.html#source 30. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40479 31. http://syn.cs.pdx.edu/~jsnow/glome/ 32. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40052 33. http://code.haskell.org/ChessLibrary/ 34. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39773 35. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xmonad-utils 36. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39710 37. http://roguestar.downstairspeople.org/ 38. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39654 39. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/scc-0.1 40. http://www.idealliance.org/papers/extreme/proceedings/html/2006/Blazevic01/… 41. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39648 42. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/twitter 43. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39522 44. http://www.haskell.org/haskellwiki/The_Monad.Reader 45. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39492 46. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/category-extras 47. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39482 48. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/sessions 49. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39352 50. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haddock-2.1.0 51. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39347 52. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ 53. http://code.google.com/p/reviewboard/ 54. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39342 55. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/diagrams-0.1 56. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39271 57. http://www.fh-wedel.de/~si/HXmlToolbox/index.html 58. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39040 59. http://code.google.com/soc/2008/haskell/about.html 60. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38992 61. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bytestring 62. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38991 63. http://lambda.uta.edu/HXQ/ 64. http://www.w3.org/TR/xquery/ 65. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38965 66. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Win32-notify-0.1 67. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38922 68. http://uebb.cs.tu-berlin.de/~magr/projects/cpuid/doc/ 69. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38870 70. http://home.telfort.nl/sp969709/emp/empug.html 71. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38773 72. http://software.complete.org/datapacker 73. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38736 74. http://darcswatch.nomeata.de/ 75. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38676 76. http://www.generic-haskell.org/ 77. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38542 78. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/graphics-drawing… 79. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38505 80. http://www.haskell.org/haskellwiki/The_Monad.Reader 81. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38419 82. http://www.well-typed.com/ 83. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38173 84. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hgdbmi 85. 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wanted: Network.Curl examples
by brad clawsie 11 Jun '08

11 Jun '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 in search of some trivial examples using Network.Curl, preferrably posted here: http://haskell.org/haskellwiki/Network.Curl some of this stuff i can figure out, but setting the curl WriteFunction, as discussed here: http://code.haskell.org/~dons/docs/curl/Network-Curl-Opts.html#t%3AWriteFun… is nonobvious. any info would be useful, curl is a great library and it would be nice if using it were more straightforward thanks brad -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (FreeBSD) iEYEARECAAYFAkhPaAAACgkQxRg3RkRK91OQrQCfTt+xzvqIAxDkqq8/P85ZZjON HWgAoK3L/1JUQjdaWHcHfutKvI3nPJUc =BfuR -----END PGP SIGNATURE-----

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running haddock and lhs2TeX
by Samuel Silva 11 Jun '08

11 Jun '08

Hello I'm using haddock to my Literate Haskell code, and it runs very well. I prefer Literate Haskell instead Haskell because old code remain untouched. It also is possible run latex over my code. But running lhs2TeX is even better. However lhs2TeX doesn't proccess with some haddock information. I won't change or format haddock documentation but using two tools is a valuable help at development. I would know that somebody solve thi issue and how? To solve this issue I build processor, using perl, that escapes characters like | and @. This preprocessor just escapes characters within \begin{code} ... \end{code}. ##################################################################### # This scripts process Literate Haskell Script itself to be process # by lhs2TeX with haddock comments. # use strict; use warnings; my @tag=(); while (<>) { if ($_ =~ /\\begin{(.*)}/) {push @tag => $1;} elsif ($_ =~ /\\end{(.*)}/ and $1 eq $tag[@tag-1]) {pop @tag;} if ( elem("code",@tag) and /(.*)--(.*)/) { print $1 => process($2) => "\n"; } else { print; } } sub process{ my ($input) = @_; $input =~ s/\|/\|\|/g; # escapes | $input =~ s/\@/\@\@/g; # escapes @ $input =~ s/\^//g; # drop ^ $input =~ s/\"/\'/g; # change " into ' return "--$input"; } sub elem { my ($x,@xs) = @_; my $res = 0; for (@xs) {$res=1 if $x eq $_} return $res; } ##################################################################### -- Don't hug that, Hugs ME! Samuel Silva

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blas: ghc-6.8.2: unable to load package `blas-0.4'
by Anatoly Yakovenko 11 Jun '08

11 Jun '08

Patric, I am trying to use your blas package, but I am getting a missing symbol error. > import Data.Matrix.Dense.IO > mm::(IOMatrix (Int,Int) Double) <- newListMatrix (1,1) [1.0] Loading package storable-complex-0.1 ... linking ... done. Loading package ieee-0.1 ... linking ... done. Loading package old-locale-1.0.0.0 ... linking ... done. Loading package old-time-1.0.0.0 ... linking ... done. Loading package random-1.0.0.0 ... linking ... done. Loading package QuickCheck-1.1.0.0 ... linking ... done. Loading package blas-0.4 ... linking ... <interactive>: /usr/lib/blas-0.4/ghc-6.8.2/HSblas-0.4.o: unknown symbol `cblas_ddot' ghc-6.8.2: unable to load package `blas-0.4' any ideas what i am missing? Thanks, Anatoly

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Re: [Haskell-cafe] Moving "forall" over type constructors
by Sean Leather 11 Jun '08

11 Jun '08

Hi, > I just found out that it *is* possible to implement the inside function, > > namely as follows: > > > > > inside :: forall t. ((forall a. Wrapper (t a))-> Wrapper (forall a. (t > > > a))) > > > inside x = Wrapper f > > > where f :: forall a. (t a) > > > f = unwrap x > > > unwrap (Wrapper z) = z > > > > I guess this solves my problem. Sorry for bothering you with this > question. > > I still find it a bit weird to write all these obfuscated identity > functions > > to make the type checker happy, though. > > As I said, the types are not isomorphic -- it you think of type > parameters as arguments you will see why. I found these examples interesting, mostly because I don't understand it very well. So, I simplified Klaus' code a bit and derived the following: ----- {-# LANGUAGE Rank2Types #-} -- Wrapper newtype W a = W { unW :: a } inside :: ((forall a. W (t a))-> W (forall a. (t a))) --inside (W x) = W x -- (a) FAILS --inside = W . unW -- (b) FAILS inside x = W (unW x) -- (c) WORKS ----- Can someone comment on the differences between the following in terms of type-checking or inference? Considering the errors I got, I'm guess the issue is the same for the pattern-matching (a) and the point-free (b) versions. Are there any pointers for developing a better understanding or intuition of this? Thanks, Sean

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