[Haskell-cafe] How to improve its performance ?

[Alexander Solla]

On Mar 17, 2010, at 8:33 PM, zaxis wrote:

>
> `allPairs list = [(x,y) | x <- list, y <- list]  ` is not what  
> `combination`
> does !
>> let allPairs list = [(x,y) | x <- list, y <- list]
>> allPairs [1,2,3]
> [(1,1),(1,2),(1,3),(2,1),(2,2),(2,3),(3,1),(3,2),(3,3)]

Yeah, I know that.  I said so specifically.  combination computes the  
power set of a list.  You said your goal was to compute a set of "two  
groups".  You don't need the power set in order to compute a set of  
pairs.  Moreover, computing the power set is a slow operation.   
Indeed, it is the source of your slowness.