Friday, January 13, 2012

Project Euler Problem 1 functionally

I'm trying to learn a bit of elisp (see Luhns Algorithm in elisp). So, to try out me elisp some more I tried the Project Euler's simplest problem, Problem 1. So, I cracked open emacs and tried out a few things, gave up and went into hibernation. A few weeks later I remembered this problem and had a go at it again. I thought I nailed it...
(defun num_check (x) (if (or (eq (mod x 3) 0) (eq (mod x 5) 0)) x 0))
(defun sum(x) (if (eq x 3) 3 (+ (num_check x) (sum (- x 1)))))
(sum 3)
3
(sum 5)
8
(sum 10)
33
(sum 1000)
Debugger entered--Lisp error: (error "Lisp nesting exceeds `max-lisp-eval-depth'")
After a bit of googling I found out the elisp only supports 300 recursive calls :(. So, I decided to take the plunge into clisp and started downloading that. Meanwhile I had some old version of scala available and tried this
Welcome to Scala version 2.9.0.1 (Java HotSpot(TM) Server VM, Java 1.6.0_20).
Type in expressions to have them evaluated.
Type :help for more information.

scala> def num_check(n: Int):Int = if ( (n % 3) == 0 || (n % 5) == 0 ) n else 0
num_check: (n: Int)Int

scala> def do_sum(x: Int):Int = if ( x == 3 ) 3 else num_check(x) + do_sum(x - 1)
do_sum: (x: Int)Int

scala> do_sum(10)
res0: Int = 33

scala> do_sum(100)
res1: Int = 2418

scala> do_sum(1000)
res2: Int = 234168
Wow, that went well and by the time I had googled to find the syntax for scala etc., clisp was downloaded and here goes
  i i i i i i i       ooooo    o        ooooooo   ooooo   ooooo
  I I I I I I I      8     8   8           8     8     o  8    8
  I  \ `+' /  I      8         8           8     8        8    8
   \  `-+-'  /       8         8           8      ooooo   8oooo
    `-__|__-'        8         8           8           8  8
        |            8     o   8           8     o     8  8
  ------+------       ooooo    8oooooo  ooo8ooo   ooooo   8

Welcome to GNU CLISP 2.44.1 (2008-02-23) <http://clisp.cons.org/>

Copyright (c) Bruno Haible, Michael Stoll 1992, 1993
Copyright (c) Bruno Haible, Marcus Daniels 1994-1997
Copyright (c) Bruno Haible, Pierpaolo Bernardi, Sam Steingold 1998
Copyright (c) Bruno Haible, Sam Steingold 1999-2000
Copyright (c) Sam Steingold, Bruno Haible 2001-2008

Type :h and hit Enter for context help.

[1]> (defun num_check (x) (if (or (eq (mod x 3) 0) (eq (mod x 5) 0)) x 0))
NUM_CHECK
[2]> (defun sum(x) (if (eq x 3) 3 (+ (num_check x) (sum (- x 1)))))
SUM
[3]> (sum 10)
33
[4]> (sum 1000)
234168

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