G'day all.
Quoting Neil Mitchell
It's nice to write functions in point free style:
f = sort . nub
But sometimes I have to add an extra case, on a certain value:
f [] = [1] f = sort . nub
But now these equations have different arities, and its rejected by Haskell.
I don't know why Haskell does it specifically, but here's why I like the behaviour: 1. Equations with different arities more often signal bugs than correct intentions. One common situation is adding an argument to a function, and accidentally leaving one equation out. 2. It's highly misleading. This: f [] = [1] f = sort . nub suggests that f is (sort . nub), which is most decidedly is not. By forcing you to add the argument: f [] = [1] f xs = sort . num $ xs it reminds you more strongly that what you're actually writing is a shorthand for this: f [] = [1] f xs@(_:_) = sort . num $ xs Cheers, Andrew Bromage