Here is the latest Caml Weekly News, for the week of June 24 to July 1, 2008.
Archive: http://groups.google.com/group/fa.caml/browse_frm/thread/c292d01cec4d72b2#Continuing the thread from last week, Nathaniel Gray said:
> Can someone summarise active patterns for us? The MSDN site > containing the paper is down at the moment. Sure. Active patterns are a lot like Wadler's "views", and thus are similar to the stuff in micmatch. With active patterns you can invoke functions (implicitly) within pattern matches and match the results, which allows you to provide a "virtual" algebraic data structure for any value you might want to match against. Here's an example from the paper (using F# syntax): open LazyList let (|Cons|Nil|) l = if nonempty(l) then Cons(hd(l),tl(l)) else Nil let rec pairSum xs = match xs with | Cons (x, Cons (y,ys)) -> consl (x+y) (lazy (pairSum ys)) | Cons (x, Nil ()) -> consl x (lazy nil) | Nil () -> nil This expands to: let rec pairSum xs = if nonempty xs then let x, ys = hd xs, tl xs if nonempty ys then let y, zs = hd ys, tl ys consl (x+y) (lazy (pairSum zs)) else consl x (lazy nil) ) else nil There are other variations presented in the paper, including parameterized patterns. These are nice for doing things like regular expression matching. Again, from the paper: let (|ParseRE|_|) re s = let m = Regex(re).Match(s) if m.Success then Some [ for x in m.Groups -> x.Value ] else None let swap s = match s with | ParseRE "(\w+)-(\w+)" [l;r] -> r ^ "-" ^ l (* See below *) | _ -> s The matching syntax here is a bit confusing because it can be hard to tell where parameters end and patterns begin. In the example above, "(\w+)-(\w+)" is a parameter and [l;r] is a pattern. There's definitely room for improvement over this syntax. There are other variations and examples in the paper. I'd definitely recommend reading it. If you still can't get it from the website I can forward you a copy off-list.
Archive: http://groups.google.com/group/fa.caml/browse_frm/thread/6c369078d4fdcea1#Martin Jambon announced:
I couldn't resist creating an OCaml social network at Ning: http://ocamlhackers.ning.com/ It's free and easy. Allows you to have your OCaml blog and exclusively OCaml friends. If you like this, join now :-)
Archive: http://groups.google.com/group/fa.caml/browse_frm/thread/dc7f818a411020d4#Dave Benjamin announced:
The PLEAC project aims to translate the source code examples of the Perl Cookbook to many programming languages. I have been working steadily for the past two years toward completing the OCaml translation. As of today, it is 70.71% complete, in between Ruby (64.43%) and Python (85.43%). http://pleac.sourceforge.net/ http://pleac.sourceforge.net/pleac_ocaml/index.html Much of my recent work has been on the file I/O chapters, which cover the topics of reading and writing to files using Pervasives and the Unix module. The file access chapter covers argument parsing, file locking, buffering and non-blocking I/O: http://pleac.sourceforge.net/pleac_ocaml/fileaccess.html The file contents chapter contains some helpful examples of working with Streams and Buffers, line-indexing of large files, and manipulation of binary data including an example of using Richard Jones' Bitmatch library to parse and "tail" Linux's binary "utmp" database of login events: http://pleac.sourceforge.net/pleac_ocaml/filecontents.html I have updated the PDF version as well, if you prefer to read PLEAC in an offline format. You can download it here: http://ramenlabs.com/pleac-pdf/pleac_ocaml.pdf As always, feedback, corrections, and contributions are more than welcome, and I will do my best to make suggested improvements. I think that, despite being somewhat Perl-centric and in need of more explanation, the OCaml PLEAC has already become a valuable resource. I refer to it frequently myself. Hopefully some day there will be a real OCaml Cookbook. In the meantime, there are a lot of practical code snippets that can save a few trips to the manual / interface files. I hope you find it useful as well.
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