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A function is a mapping from one set, called a domain, to another set, called the codomain. A function associates every element in the domain with exactly one element in the codomain. In Scala, both domain and codomain are types.
val square : Int => Int = x => x * x
A primer/refresher on the category theory concepts that most commonly crop up in conversations about Scala or FP. (Because it's embarassing when I forget this stuff!)
I'll be assuming Scalaz imports in code samples, and some of the code may be pseudo-Scala.
A functor is something that supports map.
| def isPrime(n: Long) = (2L to math.sqrt(n).toInt).forall(n % _ != 0) | |
| // val sum = (2L to 2000000L).filter(isPrime).sum | |
| val sum = 2 + (3L to 2000000L by 2).filter(isPrime).sum | |
| assert(sum == 142913828922L) |