Fork of the Hamt (hash array mapped trie) library. This fork adds a few important features in exchange for very slightly degraded performance:
- Transient mutation. This allows efficient mass operations, while retaining the safety of a persistent data structure.
- Supports using a custom key comparision function.
- Supports using a custom hash function.
The Hamt+ Api is a superset of Hamt's Api. Hamt+ supports any key type using the custom hash and key comparision functions.
Source code is in hamt.js
and generated from lib/hamt.js
. The library supports node, AMD, and use as a global.
$ npm install hamt
var hamt = require('hamt_plus');
var h = hamt.empty.set('key', 'value');
...
requirejs.config({
paths: {
'hamt': 'path/to/hamt_plus/'
}
});
require(['hamt'], function(hamt) {
var h = hamt.empty.set('key', 'value');
...
});
Hamt+ provides a method chaining interface and free functions for updating and querying the map. Both APIs provide identical functionality, but the free functions are designed for binding and composition, while the method chaining API is more legible and more Javascripty.
HAMTs are is persistent, so operations always return a modified copy of the map instead of altering the original.
Most update and lookup methods have two versions: one that takes a key and uses an internal hash function to compute its hash, and a version that takes a custom computed hash value.
var h = hamt.empty.set('key', 'value');
var h2 = hamt.empty.setHash(5, 'key', 'value');
h.get('key') === 'value'
h2.getHash(5, 'key') === 'value'
If using a custom hash, you must only use the *Hash
variant of functions to interact with the map.
// Because the internally computed hash of `key` is not `5`, a direct
// look will not work.
h2.get('key') === undefined
// You must use `getHash` with the same hash value originally passed in.
h2.getHash(5, 'key') === 'value'
Create a new, empty map.
config
โ Optional. Holds the custom hash and key compare functions:{ hash: myHashFunction, keyEq: myKeyCompareFunction }
const Vec2 = (x, y) => ({ x: x, y: y });
const vecMap = hamt.make({
hash: (value) => hamt.hash(value.x + ',' + value.y),
keyEq: (a, b) => a.x === b.x && a.y === b.y
});
vecMap = vecMap.set(Vec2(1, 2), 'value');
vecMap.get(Vec2(1, 2)) === 'value'
An empty map.
Uses default key compare function and hash functions.
Is a map empty?
This is the correct method to check if a map is empty. Direct comparisons to hamt.empty
will not work.
Lookup the value for key
in map
.
key
- String key.map
- Hamt map.
var h = hamt.empty.set('key', 'value');
h.get('key') === 'value'
hamt.get('key', k) === 'value'
h.get('no such key') === undefined
Same as get
but uses a custom hash value.
Same as get
but returns alt
if no value for key
exists.
alt
- Value returned if no such key exists in the map.key
- String key.map
- Hamt map.
Does an entry for key
exist in map
?
key
- String key.map
- Hamt map.
var h = hamt.empty.set('key', 'value');
h.has('key') === true
h.has('no such key') === false
Same as tryGet
but uses a custom hash value.
Set the value for key
in map
.
value
- Value to store. Hamt supports all value types, including: literals, objects, falsy values, null, and undefined. Keep in mind that only the map data structure itself is guaranteed to be immutable. Using immutable values is recommended but not required.key
- String key.map
- Hamt map.
Returns a new map with the value set. Does not alter the original.
var h = hamt.empty
.set('key', 'value');
.set('key2', 'value2');
var h2 = h.set('key3', 'value3');
h2.get('key') === 'value'
h2.get('key2') === 'value2'
h2.get('key3') === 'value3'
// original `h` was not modified
h.get('key') === 'value'
h.get('key2') === 'value2'
h.get('key3') === undefined
Same as set
but uses a custom hash value.
Update the value stored for key
in map
.
f
- Function mapping the current value to the new value. If no current value exists, the function is invoked with no arguments.key
- String key.map
- Hamt map.
Returns a new map with the modified value. Does not alter the original.
var h = hamt.empty
.set('i', 2);
var h2 = h.modify('i', x => x * x);
h2.get('i') === 4
h.get('i') === 2
h2.count() === 1
h.count() === 1
// Operate on value that does not exist
var h3 = h.modify('new', x => {
if (x === undefined) {
return 10;
}
return -x;
});
h3.get('new') === 10
h3.count() === 2
Same as modify
but uses a custom hash value.
Remove key
from map
.
key
- String key.map
- Hamt map.
Returns a new map with the value removed. Does not alter the original.
var h = hamt.empty
.set('a', 1)
.set('b', 2)
.set('c', 3);
var h2 = h.remove('b');
h2.count() === 2;
h2.get('a') === 1
h2.get('b') === undefined
h2.get('c') === 3
Same as remove
but uses a custom hash value.
Get number of elements in map
.
map
- Hamt map.
hamt.empty.count() === 0;
hamt.empty.set('a', 3).count() === 1;
hamt.empty.set('a', 3).set('b', 3).count() === 2;
Fold over the map, accumulating result value.
f
- Function invoked with accumulated value, current value, and current key.z
- Initial value.map
- Hamt map.
Order is not guaranteed.
var max = hamt.fold.bind(null,
(acc, value, key) => Math.max(acc, value),
0);
max(hamt.empty.set('key', 3).set('key', 4)) === 4;
Get an Javascript iterator to all key value pairs in map
.
map
- Hamt map.
Order is not guaranteed.
Array.from(hamt.empty.entries()) === [];
Array.from(hamt.empty.set('a', 3).entries()) === [['a', 3]];
Array.from(hamt.empty.set('a', 3).set('b', 3).entries()) === [['a', 3], ['b', 3]];
You can also iterated directly over a map with ES6:
const h = hamt.empty.set('a', 3).set('b', 3);
for (let [key, value] of h)
...
Array.from(h) === [['a', 3], ['b', 3]];
Get an Javascript iterator to all keys in map
.
map
- Hamt map.
Order is not guaranteed.
Array.from(hamt.empty.keys()) === [];
Array.from(hamt.empty.set('a', 3).keys()) === ['a'];
Array.from(hamt.empty.set('a', 3).set('b', 3).keys()) === ['a', 'b'];
Get an Javascript iterator to all values in map
.
map
- Hamt map.
Order is not guaranteed. Duplicate entries may exist.
Array.from(hamt.empty.values()) === [];
Array.from(hamt.empty.set('a', 3).values()) === [3];
Array.from(hamt.empty.set('a', 3).values('b', 3).values()) === [3, 3];
Invoke function f
for each value in the map.
f
- Function invoked with(value, key, map)
.map
- Hamt map.
Order is not guaranteed.
Start the mutation of map
. The number of calls to beginMutation
is counted, but mutation itself is binary: the map is either mutable or immutable. Mutation cannot leak before the first call to beginMutation
or after the matching call to endMutation.
End the mutation of map
.
Mutate map
within the context of function f
.
const insert = ['a', 'b', 'c'];
const h = hamt.mutate(h =>
// any operations within this block may mutate `h` internally.
insert.forEach((x, i) => {
h.set(x, i);
}),
hamt.empty);
h.count() === 3;
h.get('b') === 2;
Any contributions to Hamt+ are welcome. Feel free to open an issues if you run into problems or have a suggested improvement.
To develop Hamt, fork the repo and install the development node packages:
cd hamt_plus
$ npm install
The source is written in ES6 and lives in lib/hamt.js
. Gulp and Bable are used to translate the ES6 code to an ES5 distribution found in hamt.js
. To start the compiler:
$ gulp default
Tests are written in Mocha and found in tests/*
. To run the tests:
$ mocha tests