[plt-scheme] Re: HtDP 12.4.2 question details

From: Stephen Bloch (sbloch at adelphi.edu)
Date: Tue Apr 7 08:56:26 EDT 2009

On Apr 7, 2009, at 0:10, mike <anesward at mac.com> wrote:

> For the professors out there; I cruised through sec12 until i got
> to problem 12.4.2(spent hours and i just don't get it!!).I just want
> to move on but my question is : Is 12.4.2 a pivotal problem in gauging
> one's understanding of the design recipe??? Does failure to solve the
> problem indicate a serious flaw in understanding that will impede
> under-standing of subsequent sections of the book?

The short answer, unfortunately, is "yes".  Nothing else depends  
*directly* on 12.4.2, but that problem is a real test of how well  
you've internalized the design recipe.  Make sure you've got all the  
input and output datatypes right (they can be confusing in this  
problem), make sure you've got a good suite of test cases (to many of  
which the "right answer" isn't what you think at first), fill out the  
function template, pick a not-too-simple example and write the value  
of each template item for that example, and ask yourself how to  
combine the values you've got to get the "right answer" for that  
example.  This will probably require a helper function; lather, rinse,  
repeat.  The exercise really will teach you a lot.

Steve Bloch

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