bilby.js

Serious functional programming library for JavaScript.



Features

$3

Multimethods belong to an immutable environment:

var env = λ.environment()
.method('length', λ.isArray, function(a) {
return a.length;
})
.method('length', λ.isString, function(s) {
return s.length;
})
.property('empty', function(o) {
return !this.length(o);
});

env.empty([]) == true;
env.empty([1, 2, 3]) == false;

$3

Curried and uncurried application:

var add = λ.curry(function(a, b) {
return a + b;
});
add(1)(2) == 3;
add(1, 2) == 3;

Lenses for immutable updates of nested data structures:

var person = {
name: "Brian",
address: {
number: 100,
street: "Pitt St",
state: "QLD"
}
},
addressLens = λ.objectLens('address'),
stateLens = λ.objectLens('state'),
personStateStore = stateLens.compose(addressLens).run(person),
newPerson = personStateStore.setter("TAS");

newPerson.address.state == "TAS";
person.address.state == "QLD";

$3

Option:

λ.some(3).getOrElse(0) == 3;
λ.none.getOrElse(0) == 0;

Either:

λ.left(1).fold(add(1), add(2)) == 2;
λ.right(1).fold(add(1), add(2)) == 3;

$3

Monads:

λ.Do()(
λ.some(1) >= function(x) {
return x < 0 ? λ.none : λ.some(x + 2);
}
).getOrElse(0) == 3;

Kleislis:

λ.Do()(
function(x) {
return x < 0 ? λ.none : λ.some(x + 1);
} >> function(x) {
return x % 2 != 0 ? λ.none : λ.some(x + 1);
}
)(1).getOrElse(0) == 3;

Functors:

λ.Do()(
λ.some(1) < add(2)
).getOrElse(0) == 3;

Applicatives:

λ.Do()(
λ.some(add) λ.some(1) λ.some(2)
).getOrElse(0) == 3;

Semigroups:

λ.Do()(
λ.some(1) + λ.some(2)
).getOrElse(0) == 3;

$3

Automates generating arguments for a function and shrinking them when
a test failure is found:

// Any string appended with its reverse is a palindrome.
exports.isPalindromeTest = function(test) {
var report = λ.forAll(
function(s) {
var reversed = s.split('').reverse().join('');
return isPalindrome(s + reversed);
},
[String]
);

test.ok(report.success, report.fold(
"OK",
function(inputs, tries) {
return "Failed after " + tries + " tries: " + inputs.toString();
}
));

test.done();
};

Usage

node.js:

var λ = require('bilby');

Browser: