20 Feb
                
                    2010
                
            
            
                20 Feb
                
                '10
                
            
            
            
        
    
                5:56 a.m.
            
        Also, constructions like
sortBy (compare `on` foo)
must surely be very common.
Just as a data point: I use constructions like the above very often. (Perhaps someone more enlightened than me can point out the connection to arrows?) Data.Function.on is surprisingly useful in some other contexts, too. Matthias.