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

Errors that manifest as exceptions  

in a dynamically checked language 

become compile-time errors.

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JANUARY 2012

and loops must be viewed with great suspicion. Compli-

cated control flows confuse programmers. Messy code 

often hides bugs.

Consider a real example (taken from Sean Parent): in 

many user interfaces, an item of a sequence can be moved 

to a different position in the sequence by dragging its 

screen representation over a screen representation of the 

sequence. The original solution (after cleanup and simplifi-

cation) involved 25 lines of code with one loop, three tests, 

and 14 function calls. Its author considered it messy and 

an attempt to simplify the code was made. The result was