Cover fe ature 47 january 2012 Published by the ieee computer Society 0018-9162/12/$31. 00 2012 ieee

Practice type-rich programming

So far, I’ve focused primarily on efficiency, but ef-

ficiency is irrelevant if the code contains critical errors. 

Addressing the issue of correctness requires making prog-

ress on two fronts:

 

•

eliminate programming errors (make such errors less 

likely and more easily spotted), and

 

•

make it easier to analyze a program for design errors 

(in general, make it easier to build tools that manipu-

late programs).

The distinction between a design error and a program-

ming error isn’t completely clear. My practical definition is 

that programming errors are those that can be caught by a 

good production compiler; they involve inconsistent use of 

values and don’t require extensive computation to detect. 

Design errors involve plausible-looking code that just hap-

pens to do the wrong thing. Catching design errors requires 

tools that “understand” the semantics of higher-level op-

erations. Even a compiler can be such a tool if semantic 

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1,250

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5,000

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Vector

List

Preallocated list