[racket] section 11.5 from htdp

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Sat May 28 15:30:40 EDT 2011

Follow the design recipe. 

A natural number is one of: 
 -- 0 
 -- one more than n for some natural number n

Now create a template. Then fill the gaps. 

On May 28, 2011, at 2:50 PM, Krzysztof Adamczyk wrote:

> I am having some difficulties with section 11.5 from htdp. I'm of course not the first one encountering such problems:
> http://lists.racket-lang.org/users/archive/2008-November/028325.html
> but the above thread doesn't help in any way - Mr. Felleisen confirms that one shouldn't assume that x is a natural number. But in his next post he says that the function multiply from previous exercises should be used. Am I missing or misunderstanding something? Is it possible to multiply x by x n times with my multiply function when it needs both arguments to be natural numbers? My first idea was to use a different function, say multiply-by-inexact, which uses the + operator like multiply-by-pi, but it still needs one natural argument to stop recursion. In which direction should I go to solve this? My exponent function works for natural numbers, but I don't want to miss anything important while going through this textbook.
> Krzysztof
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