hackinghat.com

The Mersenne Twiser is a random number generator that has a lot of applications, particularly in finance. After discovering that there was no Clojure implementation at Wikipedia I decided to give it a try as my first attempt at something useful in Clojure. As it turns out it’s problably not a good candidate to be implemented in a functional language because the whole thing requires modifying a mutable array for every call to (genrand).

I’m not very excited by the solution because it doesn’t seem very lispy. It much more resembles the reference implementation, and gives the same results as it for all the tests I tried.

I’m sure it could be better though.

If it’s of any use to anyone you can find it here.

Yesterday I watched Dan Weinreb talking about ITA, Lisp, and well, really, really complex stuff

The kind-of conclusion that he drew on the future of Lisp is that Clojure is the next Common Lisp. I’ve been dodging Clojure for about a year now. I bought the book from The Pragmatic Programmers when the book was in beta and eagerly followed the examples and decided it had promise. But, I figured that if I needed to really learn it (and by that I mean use it, not just talk about using it) it would have to come to me. It would do this, I reasoned, by being hard-to-ignore.

Well there seem to be more than enough smart-folks on-board now (like: Eric Normand, Bill Clementson to name only two) so I guess I better not miss the party. Not because I’m smart but because if I don’t make too much noise I can blend in and no one will notice I’m there.

So I came to the conclusion that I should try and use it for ad-hoc things that might cross-my-dome and are hard(er) to solve in non-functional languages.

For instance, this very afternoon I wanted to know how many possible hand distributions by suit there are in the card game Bridge. So four possible distributions might be:

• All 13 hearts
• 12 hearts, one diamond
• 11 hearts, one diamond, one club
• 10 hearts, one diamond, one club, one spade

The question is how many total distributions are possible?

I banged my head on the table-hard trying to figure out the answer to this. At first it seemed like a simple counting problem, but if it is I’m too simple to see it. Then I wondered if it could be an additive patitioning problem, but ordering is important so I don’t think it is. It didn’t feel NP complete. I know one thing though, at this late hour it might as well be.

1:57 bridge=> (count (for [spades (range 0 14)
                                hearts (range 0 14)
                                diamonds (range 0 14)
                                clubs (range 0 14)
                                :when (= 13 (+ spades hearts diamonds clubs))]
                                [spades hearts diamonds clubs]))
560

Functional programming rocks.

I’ve seen the future and it is git. Some believe Mercurial is the way because it is more accessible, but I’m not so sure.

We’re programmers, we love this esoteric shit. The more hardcore the better. IMHO, the force of numbers, and its pedigree, will probably make the big fat git wade through the opposition like the monster it is.

Anyway, for a few months now I’ve been seeing this github thing linked here and there, I figured it was about time I checked it out.

I went, I saw, and it was good. Fast, easy-to-use and beautifully in the spirit of free-software (you only have to pay to use it for private repositories).

So in the spirit of free lovecode I’ve added cl-mysql.

I have been thinking about a new project that I wanted to write with Mono. One of the things that I realised I would need is the ability to execute arbitrary code (user or wizard generated) that might be stored in a database.

Code … data … code.

A very dim light went on in my head telling me that that sounded very much like a Lispy problem.

However, I particularly wanted to use Mono (and not Java, say) for the solution and so I started writing my own interpreter. After about 4 hours of toil I realised that maybe I should finish reading Lisp in Small Pieces before getting carried away. But the urge to create was large, so I went looking for a Scheme interpreter written in .NET and found S#.

10 minutes of fiddling in MonoDevelop later and I had an R4RS interpreter running in .NET on Linux. I heart open source …

stkni@ubuntu:~/source/SSharp-Mono-0.38a/SSharp.Console/bin/Debug$ ./SSharp.Console.exe 

 This is: SharpScheme v0.38 - R4RS compatible Scheme interpreter.
 A pure C# port of Peter Norvig's Scheme for the .NET Framework.
 License here: http://www.norvig.com/license.html 

 Running on: Unix  

>>> (+ 1 2)
3

I am pleased to announce that cl-mysql 0.2 is ready for use!

Here are some of the highlights of v0.2

• Connection pooling - Thread safe allocation and release of connections from a central pool.
• Use result/Store result - Ability to use mysql_use_result as well as mysql_store_result. This means that CL-MYSQL should be able to handle the processing of very large datasets without running out of memory.
• Convenience functions/macros - with-rows / nth-row

The main difference between v0.1 and v0.2 is that version 0.1 didn’t really manage its connections. I decided that allowing the user to choose between pooled and non-pooled connections is a hassle. Much better then to allow the user to create as many connection pools as they want and allow them to specify the maximum and minimum number of connections that the pool can hold. After all, a single connection is simply a special case of a pool with only one connection.

However, in theory this could hurt performance when attempting to do large number of INSERT/UPDATE’s because every call would require the connection pool to be locked and a connection to be aquired. This could be overcome though by making use of the fact that CL-MYSQL will correctly pass multiple statements to the server so you could concatenate a large string of updates and execute them all at once.

The good news though is that the API has changed only very slightly in the optional arguments it accepts. However I have changed the way the result data comes back from query. Because CL-MSQL returns multiple result sets it’s necessary to place all of them into a sequence. Additionally, I did not like the way I was placing the column headers into the first item of the result data. It means you always have to allow for it. I considered doing it the way that CLSQL does it by returning the column data in a value struct but I find this awkward to manage. This is because every layer of the API (and client code) must multiple-value-bind the columns out and either repackage them as a sequence or create a new value structure to pass them up the call-chain.

Therefore I have changed the result sequence structure to be as follows:

query-result ::= (<result-set>*)
result-set ::= (<result-data> <column-data>)
result-data ::= (<row>*) | <rows-affected>
row ::= (<column>*)
column-data ::= ((<column-name> <column-type> <column-flags>)*)

I appreciate that this is a little complex, I did consider turning the result data into a struct but this complicates how the user processes the data. For this reason I have added: with-rows and nth-row to simplify the processing of this result data.

Finally, the whole thing is still only SBCL/x86 Linux compatible, that might change .

More information is available here. As always, any feedback is appreciated.