Friday, October 14, 2005

Lisp

I am learning Lisp. Why and how, i will tell later. But one thing that struck me while learning is how common Python and Lisp are. I will now present some Python/Lisp snippets. If you can read Python, you sure can read Lisp.

Here is a code for factorial in Python

def factorial(n):
if n == 0:
return 1
else:
return n * factorial(n - 1)

Now code in Lisp

(defun factorial (n)
(if (= n 0)
1
(* n (factorial (- n 1)))))


In Lisp, operators come first in the list (prefix)

so in Python if you say
(2 + 3)
it is
(+ 2 3)
in Lisp.
Python:
(2 + 3 + 4 + 5)

Lisp:
(+ 2 3 4 5)


Just assume all those paranthesis are not there. You will find it almost like Python
Here is the Lisp version with some paranthesis removed


defun factorial (n)
if (= n 0)
1
* n factorial (- n 1)


How hard is that :)

Long back ago, when i was at the peak of Python craze, i saw Lisp and was quite frustrated by all its (). I then decided that i will not learn this language ever in my life. I was wrong. It seems there are many powerful features which Lisp has, and no other language has. So only way to learn is to learn it :)

Now here is the Python and Lisp version of Tower of Hanoi. Try figure
Python:


def towerOfHanoi (disks, fromp, to, spare):
if disks:
towerOfHanoi (disks[1:], fromp, spare, to)
print "Move %s from %s to %s" % (disks[0], fromp, to)
towerOfHanoi (disks[1:], spare, to, fromp)

towerOfHanoi ([3, 2, 1], 'a', 'b', 'c')


Lisp:


(defun towerOfHanoi (disks from to spare)
(unless (endp disks)
(towerOfHanoi (cdr disks) from spare to)
(format t "Move ~A from ~A to ~A~%" (car disks) from to)
(towerOfHanoi (cdr disks) spare to from)))

(towerOfHanoi '(3 2 1) 'a 'b 'c)

5 comments:

Zeus said...

Have you thought about teaching Computer Science?

phobos said...

i am not qualified for that

uno said...

I think u are qualified
Many ppl with just B.tech teaches in colleges

neo said...

Ahem! Seems like a new craze - LISP!

Happy Coding ;-)

And say Hi to that LOGIX friend of yours .. lol .. if he is still outsourced himself to bangalore .

phobos said...

>>I think u are qualified
Many ppl with just B.tech teaches in colleges

hmm..

>>And say Hi to that LOGIX friend of yours .. lol .. if he is still outsourced himself to bangalore .

:D neo im very much sorry about that :)

others: one day i took neo along for one python meetup here, there was a talk on logix (www.livelogix.com) .. it was too much .. poor neo was gasping the whole 2 hours :D