Description

Part 1

Generators and Iterators are new ES6 features that will allow things like this:

function* fibonacci() {
 let [prev, curr] = [0, 1];
    for (;;)  {
      [prev, curr] = [curr, prev  + curr];
        yield curr;
    }
}

Using them in this way, we can do amazing things:

let seq = fibonacci();
print(seq.next());  //  
print(seq.next());  //  
print(seq.next());  //  
print(seq.next());  //  
print(seq.next());  //

The goal is to implement pseudo-generators without the use of generators.

The first thing to do is to implement the generator function:

function generator(sequencer)  {
  ...
}

generator(sequencer[, arg1, arg2, ...]) receives a sequencer function to generate the sequence and returns an object with a next() method. When the next() method is invoked, the next value is generated. The method could receive as well optional arguments to be passed to the sequencer function.

This is an example of a dummy sequencer:

function dummySeq() {
  return function() {
    return  "dummy";
  };
}

To test generator(), you could use dummySeq() in this way:

var seq = generator(dummySeq);
seq.next(); //  'dummy'
seq.next(); //  'dummy'
seq.next(); //  'dummy'
....

When you’re done, you should implement the following generators:

function  factorialSeq()  {...} //  1,  1,  2,  6,  24, ...
function  fibonacciSeq()  {...} //  1,  1,  2,  3,  5,  8,  13, ...
function  rangeSeq(start, step) {...} //  rangeSeq(1, 2)    ->  1, 3,  5,  7,  ...
function  primeSeq()  {...} //  2,  3,  5,  7,  11, 13, ...
partialSumSeq(1,  3,  7,  2,  0)  {...} //  1,  4,  11, 13, 13, end

You can use any of them in the same way:

var seq = generator(factorialSeq);
seq.next(); //  !0  = 
seq.next(); //  !1  = 
seq.next(); //  !2  = 
seq.next(); //  !3  = 
seq.next(); //  !4  = 
...

There are some sequences which are infinite and others are not. For example:

primeSeq: Is infinite partialSumSeq: Is limited to the passed values.
When the sequence is done (in finite sequences), if you call seq.next() again, it should produce an error.

Part 2

You have to implement the pipeSeq() function. This function allows you to pipe generator to some functions. Thus the generated sequence is streamed to a function.

pipeSeq() receives the sequencer function and optionally some parameters passed to the sequencer and returns and object with two methods:

pipeline(pipe): receives the pipe function and optionally some parameters passed to the pipe function. It returns itself.
invoke(): return the piped sequencer object.

This is and example to understand this:

Given this pipeline function:

function  accumulator() {
    var sum = 0;
    return  function(value) {
        sum +=  value;
        return  sum;
    };
}

//Example
var ac  = accumulator();  //  ac(1) ->  1,  ac(4) ->  5,  ac(2) ->

We could create the piped sequencer like this:

var pipedSeq  = pipeSeq(rangeSeq, 2,  3)  //  2,  5,  8,  
            .pipeline(accumulator)  //  2,  7 (5+2),  15(7+8),  26(15+
)
            .invoke();

pipedSeq is a range sequencer whose values are streamed to the
accumulator() function. This function sum the values of the sequence.

These are the expected results:

var seq = generator(pipedSeq);
seq.next(); //  
seq.next(); //  
seq.next(); //  
seq.next(); //  
...

The same pipedSeq object can have more than one pipe.

You should implement too the isEven pipe function:

function isEven(){...}

var ie = isEven(); //  ie(1) ->  {status:  false,  number:1},  ie(4)  ->  {status:  true, number:4}

Requirements

Need to run npm install to install all required packages

Running tests

To run the tests you have to run npm run tests

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eldimious / sequencers-pipeline