perlmeditation eyepopslikeamosquito Following the educational tradition of: <ul> <li><a href="http://www.rosettacode.org/">Rosetta code</a> <li><a href="http://www.ic.unicamp.br/~meidanis/courses/mc336/2006s2/funcional/L-99_Ninety-Nine_Lisp_Problems.html">99 Lisp Problems</a> <li><a href="http://svn.pugscode.org/pugs/t/examples/99problems/">99 Problems in Perl 6</a> <li>[id://589260] </ul> this meditation describes an arbitrary problem to be solved in as many different languages as possible. <readmore> I chose this particular problem purely by chance after being surprised that [id://629259|solving it in Perl] turned out to be more awkward than I'd expected. Curious as to whether this awkwardness was specific to Perl, I then tried solving it in Ruby, Python and Haskell. Hence this node. :-) The Problem Given an input string, for example <CODE>"ZBBBCZZ"</CODE>, produce a list, for example, <CODE>["Z", "BBB", "C", "ZZ"]</CODE>. That is, break the input string into pieces based on change of character. My preferred solutions in Perl, Ruby, Python and Haskell follow. Improvements welcome. Perl My favourite solution from [id://629259] was given in the first response by [tye]: <CODE> my $s = "ZBBBCZZ"; my @x; push @x, $1 while $s =~ /((.)\2*)/g; </CODE> Ruby This was discussed at length on the Ruby-Talk mailing list, with many different solutions offered. My favourite is similar to [tye]'s Perl solution: <CODE> s = "ZBBBCZZ" x = [] s.scan(/((.)\2*)/){x.push [$~[0]]} </CODE> Python This problem was also discussed on Python-list. My favourite uses Python's SML-inspired <a href="http://docs.python.org/lib/module-itertools.html">itertools library</a>: <CODE> import itertools s = "ZBBBCCZZ" x = [''.join(g) for k, g in itertools.groupby(s)] </CODE> Haskell Browsing the Haskell <a href="http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html">Data.List documentation</a>, I noticed that a Haskell solution seems trivial courtesy of Data.List's <CODE>group/groupBy</CODE> function: <CODE> group "ZBBBCCZZ" </CODE> Discussion As you might expect, the only solution that I found truly satisfying was the Haskell one :-) ... though this seems to be more of a library issue than a language one. BTW, does anyone know of a CPAN module that can solve this problem directly? I took a quick look at: <ul> <li> [cpan://List::Util] <li> [cpan://List::MoreUtils] <li> [cpan://Iterator] </ul> but didn't notice any obvious, trivial way to do it with those libraries. I'm also curious to learn about plans for Perl 6 "functional-style" libraries. I've been impressed by Haskell's libraries and hope they will help inspire some of the new Perl 6 library. Anyway, I'd find it interesting and educational to compare solutions to this little problem in a variety of other languages. So, please respond away in your favourite language! References <ul> <li><a href="http://www.rosettacode.org/">Rosetta code</a> <li><a href="http://www.ic.unicamp.br/~meidanis/courses/mc336/2006s2/funcional/L-99_Ninety-Nine_Lisp_Problems.html">99 Lisp Problems (my problem is similar to P09)</a> <li><a href="http://svn.pugscode.org/pugs/t/examples/99problems/">99 Problems in Perl 6</a> <li><a href="http://haskell.org/haskellwiki/99_Haskell_exercises">Ninety-Nine Haskell Problems</a> <li><a href="http://mail.python.org/pipermail/python-list/2007-July/451112.html">Discussion of this problem on Python-list</a> <li><a href="http://www.ruby-lang.org/en/community/mailing-lists/">Ruby-Talk mailing list</a> <li>[id://629259] <li>[id://468106] <li>[id://512768] <li>[id://589260] <li>[id://771219] <li><a href="http://mjtsai.com/blog/2002/11/25/perl_vs_python_vs_ruby/">Perl v Python v Ruby blog</a> <li><a href="http://svn.openfoundry.org/pugs/docs/Perl6/Spec/Functions.pod">Perl 6 S29 (Functions)</a> <li>[cpan://List::Util] <li>[cpan://List::MoreUtils] <li>[cpan://Iterator] <li><a href="http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html">Haskell Data.List documentation</a> <li><a href="http://docs.python.org/lib/module-itertools.html">Python itertools documentation</a> </ul> 2-sep-2007: Updated references with some more links based on the responses below. </readmore>