[Haskell-beginners] on

[Ivan Uemlianin]

Dear All

During some recent discussion about different ways of sorting a list by 
some comparison function, one of the methods suggested was like this:

    sortByFunc = sortBy (compare `on` func)

Now, I can imagine how this works, and I don't want to discuss the 
efficiency of this implementation (I imagine it's not "Schwartzian", for 
example;).  I know what the backticks do (allow infix use of a function).

My question is: what is "on"? 

I'm afraid I haven't been able to find anything about this, no doubt 
because of all the false positives coming up in searches.  Please could 
someone tell me its official title, or where I could find it in the docs?

Thanks and best wishes

Ivan


-- 
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Ivan A. Uemlianin
Speech Technology Research and Development

                    ivan at llaisdy.com
                     www.llaisdy.com
                         llaisdy.wordpress.com
                     www.linkedin.com/in/ivanuemlianin

    "Froh, froh! Wie seine Sonnen, seine Sonnen fliegen"
                     (Schiller, Beethoven)
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