This document summarizes Bahul Neel Upadhyaya's presentation on protocols and lazy sequences in Node using the Cosy library. The presentation introduces concepts like protocols, lazy sequences, tail recursion and object metadata. It provides an example of implementing term frequency-inverse document frequency (TF-IDF) using Cosy. It also describes making sequences asynchronous and integrating Socket.IO for both server and client to demonstrate streaming TF-IDF results over the network. Future work mentioned includes queues, persistent data structures and graphs.

1. To Infinity & Beyond!
Protocols & Lazy Sequences in Node
Part Deux – Sh*t Just Got Real
Bahul Neel Upadhyaya (@bahulneel)
BraveNewTalent
http://github.com/bahulneel
http://www.bravenewtalent.com

2. cosy.lang
Library Protocols
● Protocols ● ISeq
● Sequences Lazy & Async ● ISync
● Argument length dispatch ● IStream
● Tail recursion ● IPromise
● Object Identity
● Object Metadata
npm install cosy-lang

3. An Example (TF-IDF)
“Tf–idf, term frequency–inverse document frequency,
is a numerical statistic which reflects how important a word is to a
document in a collection or corpus. It is often used as a weighting
factor in information retrieval and text mining.”
- Wikipedia

4. Words
function stripWord(word) {
return word.replace(/[^-a-zA-Z_0-9]+/, '').toLowerCase();
}
function isWord(word) {
return /^[-a-zA-Z_0-9]+$/.exec(word)
}
function words(string) {
return vec(filter(isWord, map(stripWord, string.split(/ /))));
}

5. Term Frequencies
function tf(words) {
var max = 0, counts, word;
function countFeq(counts, word) {
var newCounts = clone(counts);
if ('undefined' === typeof newCounts[word]) newCounts[word] = 0;
newCounts[word] += 1;
if (newCounts[word] > max) max = newCounts[word];
return newCounts;
}
counts = reduce(countFeq, {}, words);
if (max) {
for (word in counts) {
if (counts.hasOwnProperty(word)) counts[word] /= max;
}
}
return counts;
}

6. Inverse Document Frequency
idf = fn$({
1: function (terms) {
return idf({}, 1, terms);
},
3: function (freq, docCount, terms) {
if (null === first(terms)) return null;
function calcIdf(terms) {
var docFreq, invDocFreq = {}, word;
docFreq = merge(freq, first(terms));
for (word in docFreq) {
if (docFreq.hasOwnProperty(word)) invDocFreq[word] = docCount/(1+docFreq[word]);
}
return cons(invDocFreq, idf(docFreq, docCount + 1, rest(terms)));
}
return lazy(terms, calcIdf);
}
});

7. TF-IDF
function tfIdf(documents) {
var theWords, terms, freq;
terms = map(tf, map(words, documents));
freq = idf(terms);
function calcTfIdf(tf, idf) {
var word, tfIdf = {};
for (word in tf) {
if (tf.hasOwnProperty(word)) tfIdf[word] = tf[word] * idf[word];
}
return tfIdf;
}
return map(calcTfIdf, terms, freq);
}

8. Making Sequences Asyncronous
Source Sink
● Takes an ISeq & ISync as ● Takes an IStream as it's
it's argument argument
● Extends IStream ● Extends ISeq & ISync
● Registers a tick callback ● First returns stream.skip
using the ISync interface until stream emits
● Emits first element when
● Calls tick callback when
callback is called stream emits

9. Socket IO - Server
lang.protocol.extend(lang.stream.IStream, socketServer.Socket,
["tap", function (socket, fn) {
socket.on("message", function (data) {
fn(JSON.parse(data));
});
}],
["emit", function (socket, val) {
socket.send(JSON.stringify(val));
}]
);
function server(port, callback) {
var io = socketServer.listen(port);
io.sockets.on('connection', callback);
}

10. Socker IO - Server
(function (lang, tfIdf, server) {
server(1234, function (socket) {
lang.stream.pipe(tfIdf(socket), socket);
});
})(require('cosy-lang'),
require('./lib/tf-idf'),
require('./lib/socket-server').server);

11. SocketIO - Client
lang.protocol.extend(lang.stream.IStream, socketClient.SocketNamespace,
["tap", function (socket, fn) {
socket.on("message", function (data) {
fn(JSON.parse(data));
});
}],
["emit", function (socket, val) {
socket.send(JSON.stringify(val));
}]
);
function client(addr, callback) {
var io = socketClient.connect(addr);
io.on('connect', function () {
callback(io);
});
}

12. Socket IO - Client
client("http://localhost:1234", function (socket) {
lang.stream.tap(socket, function (val) {
console.log('td-idf', val);
});
lang.stream.pipe(documents, socket);
});

13. Demo
#!

14. Future work
● Queues
● Persistent Data Structures
● Performance
● Graphs
● Persistence

15. Links
● Cosy
getcosy.org
github.com/organizations/getcosy
● Demo
github.com/bahulneel/cosy-lang-demo
● Me
@bahulneel
github.com/bahulneel

16. Fin
Questions