Re: The only decent mathematicians here are accomplished PROGRAMMERS

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Article #761

#761

From: Owen Jacobson
Date: Wed, 21 Sep 2011 04:26

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On 2011-09-20 12:05:37 +0000, David C. Ullrich said:

> On Tue, 20 Sep 2011 03:35:39 -0700 (PDT), scaaahu <scaaahu@gmail.com>
> wrote:
> 
>> I fail to see how to store an irrational number like Pi.
> 
> What's the difference?  You store code that calculates
> the first n digits on request...
> 
> Heh. As it happens I just got this book on Haskell. I haven't
> been able to install Haskell, however, so I have no idea whether
> the following code is correct. But a corrected version will
> give the digits for the irrational number .10100100010000...
> (pi would be the same except the code would be much
> more complicated):
> 
> zeroes 0 = []
> zeroes j = 0 : (zeroes (j-1))
> 
> x j = [1] ++ (zeroes j) ++ (x (j+1))
> 
> So, expanding bit by bit, x  1 evaluates to
> 
> [1] ++ (zeroes 1) ++ (x 2),
> 
> or [1,0] + (x, 2).
> 
> which evvaluates to [1,0] ++ [1,0,0] ++ (x 3),
> 
> etc.

Looks pretty good to me, plus or minus the module preamble:

---- transcript begins ----
:)owen@nj1:~/dcu$ cat Dcu.hs
module Dcu where

zeroes 0 = []
zeroes j = 0 : (zeroes (j-1))

x j = [1] ++ (zeroes j) ++ (x (j+1))

:)owen@nj1:~/dcu$ ghci
GHCi, version 6.12.3: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.

Prelude> :add Dcu
[1 of 1] Compiling Dcu              ( Dcu.hs, interpreted )
Ok, modules loaded: Dcu.

*Dcu> take 20 $ x 1
[1,0,1,0,0,1,0,0,0,1,0,0,0,0,1,0,0,0,0,0]
---- transcript ends ----

(The dollar sign there is a notational convenience; that last 
expression is equivalent to 'take 20 (x 1)'.)

Take care,

-o

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From: Owen Jacobson <angrybaldguy@gmail.com>
Newsgroups: sci.logic,sci.math,aus.science,rec.org.mensa
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