[plt-scheme] HtDP ex 11.2.4

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Fri Feb 17 21:17:32 EST 2006


 > (empty? 'a)

-- Matthias

On Feb 17, 2006, at 7:47 PM, Prabhakar Ragde wrote:

> Richard Cleis wrote:
>> I unlearned everything that I knew about programming before starting 
>> through this book, and it hasn't yet revealed the likes of "list?" or 
>> "pair?" or "atom?".  Is this problem solvable with only the now 
>> well-worn "empty?" ?
> No, because "empty?" can only be applied to something which is "empty" 
> or "(cons ...)". But you also have "symbol?", which is sufficient. 
> Remember the design recipe: base cases, then recursive cases. You're 
> allowed to assume that the input is a deep-list. --PR
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