TITLE: The Moment When Design Happens
AUTHOR: Eugene Wallingford
DATE: November 25, 2013  2:56 PM
DESC: 
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BODY:
Even when we plan ahead a bit, the design of a program
tends to evolve.  Gary Bernhardt gives an example in
<A HREF="http://blog.extracheese.org/2009/12/on_abstraction.html">
   his essay on abstraction</A>:

<BLOCKQUOTE><EM>
 If I feel the need to violate the abstraction, I need to
 reconsider how to modify the boundaries to match that need,
 rather than violating the boundaries by crossing them.

 This is the moment when design happens...
</EM></BLOCKQUOTE>

This is a hard design lesson to give students, because it
is likely to click with them only after living with the
consequences of violating the abstraction.  This requires
working with the same large program over time, preferably
one they are building along the way.

This is one of the reasons I so like our senior project
courses.  My students are building a compiler this term,
which gives them a chance to experience a moment when
design happens.  Their abstract syntax trees and symbol
tables are just the sort of abstractions that invite 
violation -- and reward a little re-design.
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