JarCastingNOTE
This project is no longer actively supported. If anyone is interested in becoming the new maintainer, don't hesitate to contact me (hughfdjackson@googlemail.com).
For an alternative, consider https://npmjs.org/package/mori.
persistent-hash-trie
Pure string:val storage, using structural sharing.
Why
This module forms a possible basis for effecient persistent datastructures; such as those found in Clojure's PersistentHashMap and PersistentVector.
Install
npm install persistent-hash-trie
Docs
Trie
var p = require('persistent-hash-trie')
var trie = p.Trie()
assoc
Returns a new Trie with the new key:value keys added.
var trie1 = p.Trie()
var trie2 = p.assoc(trie1, 'key', { value: true })
dissoc
Returns a new Trie without a specific key
var trie1 = p.assoc(p.Trie(), 'key', 'val')
var trie2 = p.dissoc(trie2, 'key')
get
Retrieves a value from a Trie.
var trie = p.assoc(p.Trie(), 'key', 'val')
p.get(trie, 'key') //= 'val'
has
Returns true or false, depending on whether the value is in the Trie.
var trie = p.assoc(p.Trie(), 'key', 'val')
p.has(trie, 'key') //= true
p.has(trie, 'not-in-here') //= false
mutable
Returns a mutable copy of a Trie, in the form of a js object.
var trie = p.assoc(p.Trie(), 'key', 'val')
p.mutable(trie) //= { key: 'val' }
keys
Returns an array of all keys in the trie
var trie = p.assoc(p.Trie(), 'key', 'val')
p.keys(trie) //= ['key']
reduce
The traditional reduce - requires seed.
// definition of `mutable` using reduce:
var mutable = function(node){
return p.reduce(node, addKeyVal, {})
}
var addKeyVal = function(o, val, key){
o[key] = val
return o
}
Can be cancelled early:
var some = function(node, predicate){
return p.reduce(node, function(seed, value){
if ( !predicate(value)) return p.reduce.Break(false)
else return true
}, true)
}
Extending assoc/dissoc/get/has
The hashing and equality functions used on the keys can be overidden by passing an opts object to assoc, dissoc, get and has.
var p = require('persistent-hash-trie')
var opts = {
eq: function(a, b){ return a === b},
hash: function(key){ return parseInt(key, 10) }
}
var vector = p.assoc(p.Trie(), 3, 'my-val', opts)
var val = p.get(vector, 3, opts)
var vector2 = p.dissoc(vector, 3, opts)
p.has(vector2, 3, opts) // false
Running tests and benchmarks
npm test and npm run benchmark are your friends.