hyleung / predicate-combinator

via http://frankthomas.name/blog/2012/08/combining_predicates_in_scala

#Predicate Combinator + Chains

Implements Predicate combinator operators (as described here), as well as predicate chain filtering.

##Predicates

###Usage

val even = Predicate[Int](x => x % 2 == 0)
val divisible_by_5 = Predicate[Int](x => x % 5 == 0)

List.range(1,11).filter(even and divisible_by_5) should be (List(10))

###Function literal implicit conversion

import Predicate.Implicits.predicateConverter

val even = (x:Int) => x % 2 == 0
val divisible_by_5 = (x:Int) => x % 5 == 0

List.range(1,11).filter(even and divisible_by_5) should be (List(10))

##Predicate Chains

###Usage

val chain = PredicateChain(even, divisibleBy5)
chain.length should be (2)

or...

val chain = even ~> divisibleBy5
chain.length should be (2)

###Implicit conversion of Traversible[A]

Automagically adds filter(PredicateChain[A]):Traversible[A] on any Traversible[A].

import PredicateChain.Implicits.convertToChainFilterable

val chain = even ~> divisibleBy5
List(3,4,5,2,10).filter(chain) should be (List(4,2,10))

###The "Kitchen Sink" example

Uses both implicit conversions, plus the fancy ~> operator (yes, I'm going to Scala abuse hell).

import PredicateChain.Implicits.convertToChainFilterable
import Predicate.Implicits.predicateConverter

List(3,4,5,2,10)
	.filter(
		((x:Int) => x % 2 == 0) ~>
		((y:Int) => y % 5 == 0)) should be (List(4,2,10))