Activating this Blog again.

Ex. 1.12 Structure and Interpretation of Computer Programs

Generating Pascal’s Triangle. Not the most optimal implementation.

; Ex 1.12
(define bin-coeffs
  (lambda (n k)
    (cond ((= k 0 ) 1)
          ((= k n ) 1)
          (else (+ (bin-coeffs (- n 1) (- k 1))
                   (bin-coeffs (- n 1) k))))))

(define pascals-triangle-row
  (lambda (n)
    (define pascals-triangle-row-iter
      (lambda (k coeff-list)
        (cond ((> k n ) coeff-list)
              (else (pascals-triangle-row-iter (+ k 1)
                                               (cons (bin-coeffs n k) coeff-list))))))
    (pascals-triangle-row-iter 0 ‘())))

(define pascals-triangle
  (lambda (d)
    (define pascals-triangle&co
      (lambda (i col)
        (cond ((= i -1) col)
              (else (pascals-triangle&co (- i 1)
                                         (cons (pascals-triangle-row i) col
                                               ))))))
    (pascals-triangle&co d ‘())))

Flash and other virtual machines on the iPhone

I think it’s pretty lame that apple does not allow any other runtimes other than it’s own. It means that if a site makes heavy use of flash or java or silverlight it’s functioanlity is off limits to an iPhone use surfing the web.

Having said that I hate flash and I can’t wait for the day when HTML css and JavaScript finally makes that proprietay framework obsolete.

Flash and other virtual machines on the iPhone

I think it’s pretty lame that apple does not allow any other runtimes other than it’s own. It means that if a site makes heavy use of flash or java or silverlight it’s functioanlity is off limits to an iPhone use surfing the web.

Having said that I hate flash and I can’t wait for the day when HTML css and JavaScript finalllyakes that proprietay framework obsolete.

Learning OCAML: A Circular Double Link List Implementation.

I’m learning OCAML these days. I just finished reading the chapter on imperative programming in OCAML so I thought I could implement a circular double link list.

This is a first attempt, and its not quite what I wanted, but I think it’ll work.

(* Ch03 Doubly Linked Lists *)

(* 3.1 *) 

type 'a cell = 
    {
      data : 'a;
      mutable prev : 'a dlinklist;
      mutable next : 'a dlinklist
    }
and 
  'a dlinklist = Empty | Cell of 'a cell
;;

(* 3.2 Circular link list *)

let add_head x cll = 
  match cll with 
    | Empty -> 
    let new_cell = 
      { data = x; prev = Empty ; next = Empty} in
    let new_cll = Cell new_cell in
    new_cell.prev <- new_cll;
    new_cell.next <- new_cll;
    new_cll
    | Cell head_cell ->
    let new_cell = 
      { data = x ; prev = Empty; next = Empty } in
    let new_list = Cell new_cell in
    let tail_cell = head_cell.prev in
    (match tail_cell with
      | Empty -> ()
      | Cell pl -> pl.next <- new_list);
    new_cell.next <- cll;
    new_cell.prev <- head_cell.prev;
    head_cell.prev <- new_list;
    new_list


;;

let add_tail x cll = 
  match cll with
    | Empty -> add_head x Empty
    | Cell head_cell ->
    let tail_cell = 
      match head_cell.prev with
        | Empty -> failwith "Incorrect State"
        | Cell tc -> tc
    in
    let new_cell = { data = x ; prev = Empty ; next = Empty } in
    let new_list = Cell new_cell in
    tail_cell.next <- new_list;
    new_cell.prev <- head_cell.prev ;
    head_cell.prev <- new_list;
    cll
;;


let get_head_cell (cll:'a dlinklist) = 
  match cll with 
    | Empty -> failwith "Empty List"
    | Cell head_cell -> head_cell
;;

let get_tail_cell cll = 
  get_head_cell ((get_head_cell cll).prev)
;;

let remove_head cll = 
  let head_cell = get_head_cell cll in
  let tail_cell = get_tail_cell cll in
  let new_head_cell = get_head_cell (head_cell.next) in
  let new_list = Cell new_head_cell in
  if head_cell.prev = Empty 
    && head_cell.next = Empty 
  then
    Empty
  else
    begin
      new_head_cell.prev <- Cell tail_cell;
      tail_cell.next <- new_list;
      new_list
    end
;;

let remove_tail cll = 
  let head_cell = get_head_cell cll in
  let tail_cell = get_tail_cell cll in
  let new_tail_cell = get_head_cell (tail_cell.prev) in
  let new_list = Cell head_cell in
  new_tail_cell.next <- new_list;
  head_cell.prev <- Cell new_tail_cell;
  new_list
;;
      

SuperFreakonomics

Just finished reading SuperFreakonomics. Was’nt as explosive as the book cover suggested. It was’nt as mind-bending as the original was but then that’s how sequels go. I might have to reread the original and then come back to this again. It might help me appreciate this more.

BodyWorlds @ the Franklin Science Institute

Bodyworlds

If you’re going to be in Philadelphia between now and Feb 9th 2009, I strongly suggest paying the Body Worlds exhibit at the Franklin Science Institute. Unfortunately, photography is not allowed so I don’t have any pictures but here’s the link.

Pandora

Pandora has begun to really dissappoint me. When I first discovered it I really enjoyed it and I discovered a lot of good music that I wouldn’t have heard otherwise.

I was even willing to stick with the service when they started placing ads between the music. Unfortunately now the music recommendation system has declined so much in quality recommendation that i can’t to be on the site formore than a few songs.

I’m not leaving pandora. Pandora has left me:(

Red prejudice

Somebody told me that in star trek: the original series, if a character or group of characters was wearing a red uniform and was sent down to an alien planet by captain Kirk the character or group would end up dead?

Has any one else noticed this?

Sometimes…

I miss being a student. I need to get back to learning stuff !