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)