A Monad for values that may not be present, or computations that may
fail. Maybe(a) explicitly models the effects that implicit in Nullable
types, thus has none of the problems associated with using null or
undefined — like NullPointerException or TypeError.
Furthermore, being a Monad, Maybe(a) can be composed in manners similar to
other monads, by using the generic sequencing and composition operations
provided for the common interface in
Fantasy Land.
Example
var Maybe = require('data.maybe')
// :: [a], (a -> Bool) -> Maybe(a)
function find(collection, predicate) {
for (var i = 0; i < collection.length; ++i) {
var item = collection[i]
if (predicate(item)) return Maybe.Just(item)
}
return Maybe.Nothing()
}
var numbers = [-2, -1, 0, 1, 2]
var a = find(numbers, function(a){ return a > 5 })
var b = find(numbers, function(a){ return a === 0 })
// Call a function only if both a and b
// have values (sequencing)
a.chain(function(x) {
return b.chain(function(y) {
doSomething(x, y)
})
})
// Transform values only if they're available:
a.map(function(x){ return x + 1 })
// => Maybe.Nothing
b.map(function(x){ return x + 1 })
// => Maybe.Just(1)
// Use a default value if no value is present
a.orElse(function(){ return Maybe.Just(-1) })
// => Maybe.Just(-1)
b.orElse(function(){ return Maybe.Just(-1) })
// => Maybe.Just(0)
Installing
The easiest way is to grab it from NPM. If you're running in a Browser
environment, you can use Browserify:
The Maybe monad
A Monad for values that may not be present, or computations that may fail.
Maybe(a)
explicitly models the effects that implicit inNullable
types, thus has none of the problems associated with usingnull
orundefined
— likeNullPointerException
orTypeError
.Furthermore, being a Monad,
Maybe(a)
can be composed in manners similar to other monads, by using the generic sequencing and composition operations provided for the common interface in Fantasy Land.Example
Installing
The easiest way is to grab it from NPM. If you're running in a Browser environment, you can use Browserify:
Using with CommonJS
If you're not using NPM, Download the latest release, and require the
data.maybe.umd.js
file:Using with AMD
Download the latest release, and require the
data.maybe.umd.js
file:Using without modules
Download the latest release, and load the
data.maybe.umd.js
file. The properties are exposed in the globalfolktale.data.Maybe
object:Compiling from source
If you want to compile this library from the source, you'll need Git, Make, Node.js, and run the following commands:
This will generate the
dist/data.maybe.umd.js
file, which you can load in any JavaScript environment.Documentation
You can read the documentation online or build it yourself:
Then open the file
docs/literate/index.html
in your browser.Platform support
This library assumes an ES5 environment, but can be easily supported in ES3 platforms by the use of shims. Just include es5-shim :)
Licence
Copyright (c) 2013 Quildreen Motta.
Released under the MIT licence.