[Haskell-cafe] Efficient Sets for Small Enumerations

[David F. Place]

Often when writing algorithms which involve set operations on small  
enumerations, I start off using Data.Set.  I soon find performance  
requires rewriting that code to use bitwise operations.  I miss the  
nice interface of Data.Set and the type checking of using a proper  
data type.

So, as an exercise in writing a library, I wrote out an  
implementation of bitwise set operations using the interface of  
Data.Set with a couple of extensions.  It provides an abstract  
interface and type checking.  Using GHC -O3, code compiles right down  
to the primitive bit-twiddling operators.  My example program (a  
sudoku solver) runs several times faster.

I'll be grateful for any feedback on this.  Perhaps something like it  
would be useful included in the standard libraries.

Cheers, David

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David F. Place
mailto:d at vidplace.com