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Applicative Functors in Scala

Posted on June 20, 2008, in Programming

The Applicative Functor pattern is an incredibly powerful abstraction. I recently added it to a branch of Scalaz. However, it would be nice if I could alter the fixity of functions so that the parentheses below are not required to make the expression right-associative.

val add = (a: Int) => (b: Int) => (c: Int) => a + b + c
val none: Option[Int] = None // Grrr Scala

// Some(24)
println(Some(7) <*> (Some(8) <*> (Some(9) > add)))

// None
println(Some(7) <*> (none <*> (Some(9) > add)))

// List(87, 88, 89, 91, 92, 93)
println(List(1, 2, 3) <*> (List(77) <*> (List(9, 13) > add)))

Having to write that silly none value is annoying too. At the very least a none function would suffice:

def none[A]: Option[A] = None

That way. I could use none[Int] and be done with it.

Still, this pattern is a nice tool to use and I will surely be using it in the future.