connective

combine predicate (bool returning) functions with propositional logic connectives (and, or, not)

installation

$ npm install connective

usage

var connective = require('connective')
var or = connective.or
var and = connective.and
var not = connective.and
 
function wearsFlannel (person) {
  return person.wearing === 'flannel'
}
 
function ridesBikes (person) {
  return person.rides === 'bikes'
}
 
var isSquare = not(or(wearsFlannel, ridesBikes))
var isHipster = and(wearsFlannel, ridesBikes)
var isLumberjack = and(wearsFlannel, not(ridesBikes))
 
var people = {
  jon: { wearing: 'flannel', rides: 'nothing'}
  kurt: { wearing: 'flannel', rides: 'bikes'}
  bob: { wearing: 'hoodie', rides: 'scooters'}
}
 
for(var name in people) {
  var person = people[name]
  console.log(name, isSquare(person), isHipster(person), isLumberjack(person))
}

about

In propositional logic, boolean statements are joined together by connectives. Logicians would call them conjunctions, disjunctions, and negations, but programmers know them as &&, ||, and !. The problem with using these language-level connective operators is that they apply at evaluation time, and thus aren't very composable.

Functions which take a value and return a boolean are known as predicates. They are useful, for example, in conditional branching, validation, and business rules.

The functions in connective let you compose predicates into composite expressions which can be used as functions and evaluated later against other data.

api

In describing function signatures below, Predicate is a function which takes any number of arguments and returns a boolean: function(...) => boolean

connective.or: function (term1 : Predicate, ..., termN : Predicate) => Predicate

Returns a Predicate combining one or more Predicate terms with a logical or (disjunction), roughly equivalent to writing

function (x) { return Predicate1(x) || Predicate2(x) }

The returned Predicate will pass through its this context and arguments to each of the Predicate terms which are necessary to evaluate the expression.

connective.and: function (term1 : Predicate, ... termN : Predicate) => Predicate

Returns a Predicate combining one or more Predicate terms with a logical and (conjunction), roughly equivalent to writing

function (x) { return Predicate1(x) && Predicate2(x) }

The returned Predicate will pass through its this context and arguments to each of the Predicate terms.

connective.not: function (term : Predicate) => Predicate

Returns a Predicate negating term, roughly equivalent to writing

function (x) { return !Predicate(x) }

The returned Predicate will pass through its this context and arguments to term

running the tests

$ npm install
$ npm test

contributors

jden jason@denizac.org

license

MIT. (c) 2013 Agile Diagnosis. See LICENSE.md