combine predicate (bool returning) functions with propositional logic connectives (and, or, not)
npm install connective$ npm install connective
js
var connective = require('connective')
var or = connective.or
var and = connective.and
var not = connective.andfunction 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$3
Returns a Predicate combining one or more Predicate terms with a logical
(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.$3
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.$3
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` $ npm install
$ npm test
jden