Hi Rafael, 2009/6/29 Rafael Gustavo da Cunha Pereira Pinto <rafaelgcpp.li...@gmail.com>: > > Hi All, > > As the ICFP 2009 contest (http://www.icfpcontest.org) approaches its end, I > decided to write down some thoughts I had while trying. > > On Friday I downloaded the task (http://www.icfpcontest.org/task-1.9.pdf), > read it for a while, and, since my goal is to finish by Xmas, went to the > swimming pool. :-D While swimming, I started to think on the problem, and > realized that the task is almost too easy for Haskell. Actually the task was > so easy, that they added a final, non-scoring, task for those who have > finished early. > > This year's task is to build a VM that runs a (simple) program that > simulates the physics of a satellite. The VM code has no branches, acting > like a huge pocket calculator. The mission is to create a simulator that > interact with this VM and maneuver the sattelite(s) on predefined patterns. > > Here is how it went: > > 1) Reading the orbiter data file: > > The orbiter data file is a stream of 32-bit unsigned integers, which are > commands, and 64-bit double precision IEEE-754 floats, which are data, > forming a 96-bit frame. For this part I decided to use the Data.Binary > module from hackage. The module is great, and it is very simple to use. But > that took me 3 hours to learn how to use it (which, with my "honey-do" list > ended up to be in Sunday morning) > > By Saturday night I was cursing "The Binary Strike Force" because > > a) get :: Word32 reads it in little-endian > b) get :: Double reads the result of an decodeFloat, which has no > resamblance at all with IEEE-754 standards > c) I spent the entire Saturday (2 hours, honey-do excluded) > thinking I was doing something wrong!! > > I was really pissed of, until I found "getWord32le" and "getWord64le", which > solved 80% of the problem. The final blow was to decode the Word64 encoded > IEEE-754 float into a Haskell float, which took me another honey-do-free > hour. > > First step solved. (BTW: I am attaching the first version to this e-mail. I > will upload to Hackage upon completion, when getIEEE754float64le and > putIEEE754float64le functions are done!)
Indeed, I found the binary format a difficulty for haskell. But in fact, hackage has a module that does the work: http://hackage.haskell.org/package/data-binary-ieee754 > 2) Running the VM: > > This is the step I am working on. A really good and obvious approach to run > the VM is to use a RWS monad, since: > > a) I have a fixed environment (the program and the input ports) > b) I have a state (the program counter, the status register and the > data memory contents) > c) I have a monoid output (the output ports) > > This is my recurrent complaint (a rant, maybe): this really important monad > is completely undocumented, left for the developer to figure out how to use > it. Even each of the singular monads (Reader, Writer and State) is poorly > documented. > > I will do some toy programs to understand each one. Let's hope I can create > a hands-on tutorial on the RWS monad. Why a monad ? Why not just a function State -> State and the use a function like iterate to do the work ? > 3) Controlling the sattelites > > This is going to be a piece of cake (aheeem! Just kidding!!). After > computing the VM iteration, another computation will take the output data > time series and estimate the next move. The next move is easy to estimate : you have the vm and simulating code at hand. Of course, making the best move is another problem. > It will be a piece of cake, considering I would have learned enough of > Haskell state monads on step 2 to have just to worry about the physics of > the problem!!! > > > I'll keep you updated as my tests go, and hopefully I will have a working > demo of the task written in Haskell by Xmas... 2010! ;-) Good luck ! Thu _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
