Infinite sequences for Node.js. Supports typical array functions and more, all evaluated lazily.
npm install infinity> Infinite sequences for Node.js
> Supports typical array functions and more, all evaluated lazily.
Joint effort of Andrew Jones, Maxim Filimonov, Leonardo Borges and Romain Prieto, during a _ThoughtWorks_ Node.js hack night.
``coffee
infinite = require 'infinity'
infinite.range 9 # naturals from 9 to infinity
infinite.cycle [1, 2, 3] # repeats 1, 2, 3 forever
infinite.iteration 2, (i) -> i*2 # all powers of 2
infinite.zip s1, s2, s3 # a steam pairing all given streams 1 to 1
infinite.cons 99, 98, stream # a new stream starting with the given fixed values
infinite.fromArray [3, 6, 8] # this one is actually finite, but still lazy
infinite.primes() # sequence of prime numbers
infinite.fibonacci() # fibonacci sequence
`
These operations create a new lazy stream:
`coffee
stream = infinite.range 1
stream.filter (i) -> i%2 == 0 # a new stream with even numbers only
stream.map (i) -> i*2 # a new stream with all elements doubled
stream.skip 2 # a new stream that starts 2 elements further
stream.takeWhile (i) -> i < 5 # a finite stream that stops at the given condition
`
And these ones resolve a stream (non lazy):
`coffeeget the first 5 elements as a javascript array
stream.take 5
Example
FizzBuzz that doesn't use loops or modulo:
coffee
naturals = infinite.range 1
threes = infinite.cycle ['', '', ' fizz']
fives = infinite.cycle ['', '', '', '', ' buzz']
concat = (arr) -> arr.join ''
infinite.zip(naturals, threes, fives).map(concat).take(20)
`Custom streams
The basic generators (range, cycle) are not always enough.... but chances are you can express your stream as a head and a tail.
The head* is a function that returns a value
The tail* is a function that returns a stream
For example the following sequence outputs every second item it's given, lazily:
coffee
skipper = (s) -> infinite.stream (-> s.first()), (-> skipper s.tail().skip(1))skipper(infinite.fibonacci()).take 5
[ 0, 1, 3, 8, 21 ]
`This can be used to implement interesting algorithms.
For example, here's the implementation of
:`coffee
primes = ->
sieve = (s) ->
h = s.head()
infinite.stream (-> h), (-> sieve s.tail().filter (x) -> x % h isnt 0)
sieve(infinite.range 2)infinite.primes().take 5
[ 2, 3, 5, 7, 11 ]
infinite.primes().filter( (i) -> i > 1000 ).take 5
[ 1009, 1013, 1019, 1021, 1031 ]
``Curious about the code?
Go to the folder you just cloned:
shell
npm install
npm test
``