Infinite sequences for Node.js
Supports typical array functions and more, all evaluated lazily.
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:
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):
FizzBuzz that doesn't use loops or modulo:
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)
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:
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
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:
npm install npm test