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Created April 2, 2015 20:50
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on
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example
> let a = [1]
> let b = [2]
> a + b
<interactive>:5:1:
No instance for (Num [t0]) arising from a use of ‘it’
In a stmt of an interactive GHCi command: print it
> (on (+) head) a b
3
@r00k
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r00k commented Apr 2, 2015 

on :: (b -> b -> c) -> (a -> b) -> a -> a -> c

@r00k
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r00k commented Apr 2, 2015

Reads quite nicely infix:

((+) `on` head) a b

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