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I've already wrote something about OptParse last month. Today I discovered how to create a new option (that is not a string, int or bool) and validate it within the arg parser.

So suppose we want to write an application that can output both txt and html and we want the user to specify the format with command line option. One way would be to use a StdOpt.str_option - eventually with a default option - and to retrive it in application code with OptParse.Opt.get.

Every now and then I need to write a simple combinatorial algorithm. Using monads this is fairly easy and concise, but probably not the fastest way to do it. We start with the definition of a few functions in terms of the List module. The function themselves are kinda of self explanatory.

A small ocaml implementation of the Bron–Kerbosch algorithm to list all maximal cliques in an undirected graph. The description of the algorithm is on wikipedia. http://en.wikipedia.org/wiki/Bron–Kerbosch_algorithm . The example given is the same as in the wikipedia page.

I recently discovered the extLib OptPase module [1] . It's a very nice and complete replacement for the good old Arg in the standard library. I'm gonna give a small example on how to use it. I hope this can be useful to somebody.

I first build an Option module to clearly separate the options handling from the rest of my program. To keep it short we add only two options, debug and output. Debug has a short and long option, output is only a string.

The other day I needed a small xml parser to convert an xml document into a different format. First I tried xml-light. This is a simple parser all written in ocaml that stores the parser xml document in an ocaml data structure. This data structure can be user to access various fields of the xml document. It does not offer a dom-like interface, but actually I consider this a feature. Unfortunately xml-light is terribly slow.

The Pervasive.in_channel in the ocaml std library is not extensible. If you want to mix different in_channel, for example, one from Pervasive and on from the Gzip library, then you are in trouble. The good fellows of extlib solved this problem providing an extensible stream data type in the IO library [1] .

BDDs or Binary Decision Diagrams are a method of representing boolean expressions. I searched the net for available BDD libraries (I've considered different BDD variants in my research). In particular I focused on OCaml implementations. My conclusion is that as today there is no viable native implementation of an efficient bdd library. It seems common knowledge (take this cum granis salis , I haven't done any work in this direction) that the fastest bdd library is buddy, but there are not OCaml bindings to it.

Adding a custom parser in the old camlp4 (now camlp5) was relatively easy. The new camlp4 is quite different. The problem was discussed in two recent threads in the ocaml mailing list here and here.

The main point is to provide a new Lexer module with a compatible signature with the Camlp4 lexer.

The other day I read the article: "Recursive Subtyping revealed". A Functional Pearl by Gapeyev, Levin and Pierce. This is a bit of code I wrote to convince myself of the algorithm described in the paper.

You can get the article here

Recently I tried to answer to a problem posed on the OCaml mailing list. Basically the problem is how to compile using ocamlbuild using ocamlfind and camlp4. The Camlp4 wiki has already all the ingredients. Here I mix them up in a short example.

1. _tags : is the ocamlbuild dep file
2. bar.ml : is a ml file that uses the syntax extension pa_float to compile.
3. foo.ml : is a ml file that depends on bar.ml and the str module (fetched via ocamlfind)
4. pa_float.ml : is the source code of the camlp4 syntax extension.

The code

_tags