Thursday 17 December 2015

nginx: See Active connections / Connections Per Seconds

How do I monitor my nginx server status and connections requests per seconds under Linux or Unix like operating systems?

nginx server has a module called HttpStubStatusModule. This module provides the ability to get some status from nginx. You will get the following information:
  1. Number of all open connections.
  2. Stats about accepted connections.
  3. Connections per second and so on.

Configuration

Edit nginx.conf file:
# vi nginx.conf
Add or append the following in context location:
 
   location /nginx_status {
        # Turn on stats
        stub_status on;
        access_log   off;
        # only allow access from 192.168.1.5 #
        allow 192.168.1.5;
        deny all;
   }
 
Save and close the file. Reload nginx server:
# service nginx reload
OR
# nginx -s reload

Test it

Open a web-browser and type the following url:
http://your-domain-name-here/nginx_status
OR
http://ip.address.here/nginx_status
Sample outputs:
Fig.01: nginx Status Monitor with HttpStubStatusModule
Fig.01: nginx Status Monitor with HttpStubStatusModule

Where,
  1. 586 = Number of all open connections
  2. 9582571 = Accepted connections
  3. 9582571 = Handled connections
  4. 21897888 = Handles requests




Sunday 13 December 2015

Sunday 6 December 2015

The Recipe for the World's Largest Rails Monolith by Akira Matsuda

The Recipe for the World's Largest Rails Monolith


by Akira Matsuda



Kage (kah-geh) is a shadow proxy server to duplex HTTP requests

Kage (kah-geh) is a shadow proxy server to duplex HTTP requests


https://github.com/cookpad/kage

Kage (kah-geh) is an HTTP shadow proxy server that sits between clients and your server(s) to enable "shadow requests".
Kage can be used to duplex requests to the master (production) server and shadow servers that have newer code changes that are going to be deployed. By shadowing requests to the new code you can make sure there are no big/surprising changes in the response in terms of data, performance and database loads etc.
Kage is built with EventMachine and em-proxy and all shadow requests are done asynchronously, while responses from master are sent back to the client without blocking the network, so clients will never notice any delays even when shadow traffic is made.
You can customize the behavior of Kage with simple callbacks, when it chooses which backends to send shadow requests to (or not at all), appends or deletes HTTP headers per backend, and examines the complete HTTP response (including headers and body).

RRRSpec

RRRSpec enables you to run RSpec in a distributed manner.
This is developed for the purpose to obtain the fault-tolerance properties to process-failures, machine-failures, and unresponsivenss of processes in the automated testing process.
RRRSpec is used in production as a CI service, running 60+ RSpec processes concurrently, and it undergoes those failures, which include lots of rb_bugs, assertion errors, and segmentation faults.

https://github.com/cookpad/rrrspec

SwitchPoint

Switching database connection between readonly one and writable one.


https://github.com/eagletmt/switch_point


Suppose you have 4 databases: db-blog-master, db-blog-slave, db-comment-master and db-comment-slave. Article model and Category model are stored in db-blog-{master,slave} and Comment model is stored in db-comment-{master,slave}.

Quine Relay

This is a Ruby program that generates Scala program that generates Scheme program that generates ...(through 100 languages in total)... REXX program that generates the original Ruby code again.

https://github.com/mame/quine-relay

How Digital Disruption Is Redefining Industries


Digital Vortex
How Digital Disruption Is Redefining Industries

http://www.imd.org/uupload/IMD.WebSite/DBT/Digital_Vortex_06182015.pdf

Friday 27 November 2015

Riemann monitors distributed systems.

Riemann streams are just functions which accept an event. Events are just structs with some common fields like :host and :service You can use dozens of built-in streams for filtering, altering, and combining events, or write your own.
Since Riemann's configuration is a Clojure program, its syntax is concise, regular, and extendable. Configuration-as-code minimizes boilerplate and gives you the flexibility to adapt to complex situations.

I wrote Riemann for operations staff trying to keep a large, dynamic infrastructure running with unreliable but fault-tolerant components. For engineers who need to understand the source of errors and performance bottlenecks in production. For everyone fed up with traditional approaches; who want something fast, expressive, and powerful.
See problems faster

Traditional monitoring systems run polling loops every five minutes, or roll up metrics on a minutely basis. In a Riemann infrastructure, clients (including stand-alone pollers) *push* their events to Riemann, which makes them visible within milliseconds. Low latencies let you see outages faster--and know the instant you've fixed the problem.
Throughput depends on what your streams *do* with events, but a stock Riemann config on commodity x86 hardware can handle *millions* of events per second at sub-ms latencies, with 99ths around 5ms. Riemann is fully parallel and leverages Clojure and JVM concurrency primitives throughout.



http://riemann.io/
Developer Environment:


Developers are all switching between tabs to view deployments, logs, commits etc!

My next project is to make a "Developers Physical Environment"


Using a Raspberry Pi connect multiple screens and display on each

  • 1. Server logs, 
  • 2. Git commits
  • 3.Newrelic performance 
  • 4. Deployemtn Logs

and more!
Next weekend project todo:

Sunday 22 November 2015

AWS Architecture Center


The AWS Architecture Center is designed to provide you with the necessary guidance and application architecture best practices to build highly scalable and reliable applications in the AWS cloud.



https://aws.amazon.com/architecture/

nginx

Thursday 19 November 2015

Friday 13 November 2015

md file table of contents

I created two options to generate a toc for github-flavored-markdown:
DocToc Command Line Tool (source) requires node.js

Installation:
npm install -g doctoc
Usage:
doctoc . to add table of contents to all markdown files in the current and all sub directories.


http://stackoverflow.com/questions/9721944/automatic-toc-in-github-flavoured-markdown

Wednesday 21 October 2015

using ansible

Download and install VirtualBox
Download and install vagrant

$ vagrant init tower http://vms.ansible.com/ansible-tower-2.3.1-virtualbox.box
$ vagrant up
$ vagrant ssh


Read more : http://www.ansible.com/tower-trial

Ioannis@192 ~ $ vagrant init tower http://vms.ansible.com/ansible-tower-2.3.1-virtualbox.box
A `Vagrantfile` has been placed in this directory. You are now
ready to `vagrant up` your first virtual environment! Please read
the comments in the Vagrantfile as well as documentation on

`vagrantup.com` for more information on using Vagrant.



Ioannis@192 vagrant $ vagrant up
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Box 'tower' could not be found. Attempting to find and install...
    default: Box Provider: virtualbox
    default: Box Version: >= 0
==> default: Box file was not detected as metadata. Adding it directly...
==> default: Adding box 'tower' (v0) for provider: virtualbox
    default: Downloading: http://vms.ansible.com/ansible-tower-2.3.1-virtualbox.box
==> default: Successfully added box 'tower' (v0) for 'virtualbox'!
==> default: Importing base box 'tower'...
==> default: Matching MAC address for NAT networking...
==> default: Setting the name of the VM: vagrant_default_1445436657938_42127
==> default: Clearing any previously set network interfaces...
==> default: Preparing network interfaces based on configuration...
    default: Adapter 1: nat
    default: Adapter 2: hostonly
==> default: Forwarding ports...
    default: 22 => 2222 (adapter 1)
==> default: Running 'pre-boot' VM customizations...
==> default: Booting VM...
==> default: Waiting for machine to boot. This may take a few minutes...
    default: SSH address: 127.0.0.1:2222
    default: SSH username: vagrant
    default: SSH auth method: private key
    default: Warning: Connection timeout. Retrying...
    default: 
    default: Vagrant insecure key detected. Vagrant will automatically replace
    default: this with a newly generated keypair for better security.
    default: 
    default: Inserting generated public key within guest...
    default: Removing insecure key from the guest if it's present...
    default: Key inserted! Disconnecting and reconnecting using new SSH key...
==> default: Machine booted and ready!
==> default: Checking for guest additions in VM...
    default: The guest additions on this VM do not match the installed version of
    default: VirtualBox! In most cases this is fine, but in rare cases it can
    default: prevent things such as shared folders from working properly. If you see
    default: shared folder errors, please make sure the guest additions within the
    default: virtual machine match the version of VirtualBox you have installed on
    default: your host and reload your VM.
    default: 
    default: Guest Additions Version: 4.3.26
    default: VirtualBox Version: 5.0
==> default: Setting hostname...
==> default: Configuring and enabling network interfaces...
==> default: Mounting shared folders...

    default: /vagrant => /Users/Ioannis/Development/vagrant




Ioannis@192 vagrant $ vagrant ssh
Last login: Mon Oct  5 22:04:50 2015 from 10.0.2.2

  Welcome to Ansible Tower!

  Log into the web interface here:

    https://10.42.0.42/

    Username: admin
    Password:  

  The documentation for Ansible Tower is available here:

    http://www.ansible.com/tower/

  For help, email support@ansible.com
-bash: warning: setlocale: LC_CTYPE: cannot change locale (UTF-8): No such file or directory

[vagrant@ansible-tower ~]$ 

Saturday 10 October 2015

Το κομμάτι που λείπει συναντά το μεγάλο Ο

Η ιστορία μιλά για τη μοναξιά και την ανάγκη να ανήκεις. Την ανάγκη να βρεις αυτό που σε συμπληρώνει, ώστε να "κυλήσεις" στη ζωή μαζί του. Μιλά για την εναγώνια αναζήτηση αυτού του άλλου, που θα έρθει ως «από μηχανής θεός», να κλείσει το μέσα μας κενό, να δώσει νόημα στη ζωή μας. Αυτό το άλλο, που πιστεύουμε, ότι θα μας αναγνωρίσει και θα το αναγνωρίσουμε "μαγικά".

Στη διάρκεια αυτής της αναζήτησης θα κάνουμε πολλά: θα μασκαρευτούμε, θα τρομάξουμε, θα μπερδευτούμε, θα γελοιοποιηθούμε, θα ελπίσουμε... Και τελικά, κάποτε, θα βρούμε το ιδανικό μας άλλο, αυτό που μας χωρά και το χωράμε. Και ευτυχώς θα αρχίσουμε επιτέλους να «κυλάμε»...να ζούμε...Τι κρίμα μόνο, που κανείς δεν μας είπε και εμείς ποτέ δεν σκεφτήκαμε, ότι κυλώντας...αλλάζεις! Και έτσι αυτό που ξεκίνησε σαν απόλυτο ταίριασμα, στην πορεία αρχίζει να μας στενεύει και να το στενεύουμε...Και μετά τι....Μετά πάλι από την αρχή: προσμονή και μοναξιά... Μέχρι τη στιγμή που θα εμφανιστεί κάτι, κάποιος, που τίποτα δεν ζητά και τίποτα δεν του λείπει, (ένα Μεγάλο, ολοστρόγγυλο, πλήρες Ο), για να μας κάνει την απλή ερώτηση:

"Γιατί δεν κυλάς μόνο σου;"
"Μόνο μου; ένα Κομμάτι-που-λείπει (τριγωνικής μορφής) δεν μπορεί να κυλήσει μόνο του".
"Αλήθεια, προσπάθησες ποτέ;" ρώτησε το Μεγάλο Ο.
"Οι γωνίες μου είναι πολύ μυτερές" είπε το Κομμάτι-που-λείπει. "Δεν είμαι φτιαγμένο για να κυλάω μόνο μου!"
"Οι γωνίες και τα σχήματα αλλάζουν" είπε το Μεγάλο Ο...
"Αλλάζουν";

Σιωπή...Περισυλλογή...Απόπειρα....Προσπά­θεια....Κίνηση....Και επιτέλους αρχίζει το ταξίδι...η μεταμόρφωση...η ζωή...

"Το Κομμάτι που λείπει συναντά το Mεγάλο Ο", μιλά απλά και αληθινά για αυτό που όλοι ξέρουμε, αλλά ελάχιστοι κατανοούμε και ακόμα ελαχιστότεροι κάνουμε πράξη στη ζωή μας: η ολοκλήρωση και ευτυχία μας, είναι πρωτίστως μια προσωπική υπόθεση. Κανείς δεν μπορεί να μας την επιβάλει ή ακόμα και να μας τη χαρίσει «έξωθεν». Και ίσως δεν γίνεται αλλιώς: για να συν-υπάρξουμε κάποτε με κάποιον ή κάτι, πρέπει πρώτα να υπάρξουμε σαν αυτοκαθοριζόμενες οντότητες. Η συν-ύπαρξη χρειάζεται δυο...όχι δυο μισά, αλλά δυο ολόκληρα. Δυο Μεγάλα ολοστρόγγυλα Ο, που τίποτα δεν χρειάζονται και τίποτα δεν τους λείπει...Δύο ολόκληρα που συμπορεύονται από καθαρή αγάπη. Όχι από ανάγκη ούτε από συμφέρον. Δυο ολόκληρα που τα ενώνει η επιλογή. Όχι η ελπίδα, ούτε ο φόβος.... Αν έτσι αντικρίσουμε τη ζωή μας, ίσως πάψουμε να μεμψιμοιρούμε, να τα βάζουμε με τους άλλους, να είμαστε απαθής ή μοιρολάτρες. Αν δεν περιμένουμε την ευτυχία να μας χτυπήσει την πόρτα, αλλά τραβήξουμε εμείς κατά κει, αν μη τι άλλο, σίγουρα στο τέλος, όποιο κι αν είναι, θα έχουμε κάνει ένα πολύ ενδιαφέρον ταξίδι!

Wednesday 6 May 2015

Tuesday 28 April 2015

OWASP Zed Attack Proxy Project - OWASP

The new tool i found 
The Zed Attack Proxy (ZAP) is an easy to use integrated penetration testing tool for finding vulnerabilities in web applications.



Monday 20 April 2015

javascript console.table

Web Messaging or cross-document messaging

Web Messaging or cross-document messaging, is an API introduced in the WHATWG HTML5draft specification, allowing documents to communicate with one another across different origins, or source domains


Example[edit]

Consider we want document A located on example.net to communicate with document B located on example.com, which is contained within an iframe or popup window.[1] The JavaScript for document A will look as follows:
var o = document.getElementsByTagName('iframe')[0];
o.contentWindow.postMessage('Hello B', 'http://example.com/');
The origin of our contentWindow object is passed to postMessage. It must match the origin of the document we wish to communicate with (in this case, document B). Otherwise, a security error will be thrown and the script will stop.[3] The JavaScript for document B will look as follows:
function receiver(event) {
 if (event.origin == 'http://example.net') {
  if (event.data == 'Hello B') {
   event.source.postMessage('Hello A, how are you?', event.origin);
  }
  else {
   alert(event.data);
  }
 }
}
window.addEventListener('message', receiver, false);
An event listener is set up to receive messages from document A. Using the origin property, it then checks that the domain of the sender is the expected domain. Document B then looks at the message, either displaying it to the user, or responding in turn with a message of its own for document A.[1]


http://en.wikipedia.org/wiki/Web_Messaging

rails validations validate html

Rails Route verification file

Sunday 19 April 2015

.css to .scss and replace background image

change .css to .scss and replace background image

use image-url helper because we use cdn


Test it here: http://rubular.com/r/jp9hczSTHY

Wednesday 25 March 2015

Applied Philosophy, a.k.a. "Hacking"

Every system has two sets of rules: The rules as they are intended or commonly perceived, and the actual rules ("reality"). In most complex systems, the gap between these two sets of rules is huge.

Sometimes we catch a glimpse of the truth, and discover the actual rules of a system. Once the actual rules are known, it may be possible to perform "miracles" -- things which violate the perceived rules.

Hacking is most commonly associated with computers, and people who break into or otherwise subvert computer systems are often called hackers. Although this terminology is occasionally disputed, I think it is essentially correct -- these hackers are discovering the actual rules of the computer systems (e.g. buffer overflows), and using them to circumvent the intended rules of the system (typically access controls). The same is true of the hackers who break DRM or other systems of control.

Writing clever (or sometimes ugly) code is also described as hacking. In this case the hacker is violating the rules of how we expect software to be written. If there's a project that should take months to write, and someone manages to hack it out in a single evening, that's a small miracle, and a major hack. If the result is simple and beautiful because the hacker discovered a better solution, we may describe the hack as "elegant" or "brilliant". If the result is complex and hard to understand (perhaps it violates many layers of abstraction), then we will call it an "ugly hack". Ugly hacks aren't all bad though -- one of my favorite personal hacks was some messy code that demonstrated what would become AdSense (story here), and although the code was quickly discarded, it did it's job.

Hacking isn't limited to computers though. Wherever there are systems, there is the potential for hacking, and there are systems everywhere. Our entire reality is systems of systems, all the way down. This includes human relations (see The Game for an very amusing story of people hacking human attraction), health (Seth Roberts has some interesting ideas), sports (Tim Ferriss claims to have hacked the National Chinese Kickboxing championship), and finance ("too big to fail").

We're often told that there are no shortcuts to success -- that it's all a matter of hard work and doing what we're told. The hacking mindset takes there opposite approach: There are always shortcuts and loopholes. For this reason, hacking is sometimes perceived as cheating, or unfair, and it can be. Using social hacks to steal billions of dollars is wrong (see Madoff). On the other hand, automation seems like a great hack -- getting machines to do our work enabled a much higher standard of living, though as always, not everyone sees it that way (the Luddites weren't big fans).

Important new businesses are usually some kind of hack. The established businesses think they understand the system and have setup rules to guard their profits and prevent real competition. New businesses must find a gap in the rules -- something that the established powers either don't see, or don't perceive as important. That was certainly the case with Google: the existing search engines (which thought of themselves as portals) believed that search quality wasn't very important (regular people can't tell the difference), and that search wasn't very valuable anyway, since it sends people away from your site. Google's success came in large part from recognizing that others were wrong on both points.

In fact, the entire process of building a business and having other people and computers do the work for you is a big hack. Nobody ever created a billion dollars through direct physical labor -- it requires some major shortcuts to create that much wealth, and by definition those shortcuts were mostly invisible to others (though many will dispute it after the fact). Startup investing takes this hack to the next level by having other people do the work of building the business, though finding the right people and businesses is not easy.

Not everyone has the hacker mindset (society requires a variety of personalities), but wherever and whenever there were people, there was someone staring into the system, searching for the truth. Some of those people were content to simply find a truth, but others used their discoveries to hack the system, to transform the world. These are the people that created the governments, businesses, religions, and other machines that operate our society, and they necessarily did it by hacking the prior systems. (consider the challenge of establishing a successful new government or religion -- the incumbents won't give up easily)

To discover great hacks, we must always be searching for the true nature of our reality, while acknowledging that we do not currently possess the truth, and never will. Hacking is much bigger and more important than clever bits of code in a computer -- it's how we create the future.

Or at least that's how I see it. Maybe I'll change my mind later.

See also: "The Knack" (and the need to disassemble things)

Paul Buchheit

That's the vision of WebRTC.

Imagine a world where your phone, TV and computer could all communicate on a common platform. Imagine it was easy to add video chat and peer-to-peer data sharing to your web application. That's the vision of WebRTC.



http://www.html5rocks.com/en/tutorials/webrtc/basics/

method_missing to object

Wednesday 18 March 2015

Tunnelss a proxy from HTTPS to HTTP for POW

The Magic

Tunnelss is a mix between the tunnels gem and the powssl script.
  1. It builds a root-level certificate (a Certificate Authority) and registers it as a trusted root certificate (you will need to do it manually for Firefox).
  2. It generates a SSL certificate matching the Pow .dev domains.
  3. It runs an EventMachine server which acts as proxy from HTTPS to HTTP (just like tunnels), using the generated certificate so that your browser will not complain your SSL connection is not valid!

https://github.com/rchampourlier/tunnelss

Tunnelss


Installation

$ gem install tunnelss
If you're using rbenv:
$ rbenv rehash

Run

$ sudo tunnelss
Don't worry, the first time you launch it it will generate a certificate and ask for your permission to add it to trusted authorities (see The Magic above for more details).
If you are using rvm:
$ rvmsudo tunnelss








Visit https://myproject.dev :D



namespaced subdomain in rails

top level cookie in rails

Wednesday 11 March 2015

Monday 2 March 2015

CSE341: Programming Languages, Winter 2013

http://courses.cs.washington.edu/courses/cse341/13wi/



CSE341: Programming Languages, Winter 2013



Course Information



Course Materials

Material in the future naturally subject to change in terms of coverage or schedule
  1. Unit 1: ML Functions, Tuples, Lists, and More    Reading Notes    Videos
  2.   L1. Jan 7-9: Course Mechanics, ML Variable Bindings   slides: pptx   pdf   pdf6up   code: sml
  3.   L2. Jan 9: Functions, Pairs, Lists   slides: pptx   pdf   pdf6up   code: sml
  4.   S1. Jan 10: Emacs, SML Mode, Shadowing, Error Messages   slides: pdf   pdf4up   code: errors.sml   solutions.sml
  5.   L3. Jan 11: Local Bindings, Options, Benefits of No Mutation   slides: pptx   pdf   pdf6up   code: sml
  6.  
  7. Unit 2: Datatypes, Pattern Matching, Tail Recursion, and More    Reading Notes    Videos
  8.   L4. Jan 14: Records, Datatypes, Case Expressions   slides: pptx   pdf   pdf6up   code: sml
  9.   L5. Jan 16: More Datatypes and Pattern Matching   slides: pptx   pdf   pdf6up   code: sml
  10.   S2. Jan 17: Type Synonyms, Polymorphism, & More   slides:   pptx   pdf   code:   synonyms.sml   generics.sml  equality.sml   fun_patterns.sml
  11.   L6. Jan 18: Nested Pattern-Matching, Exceptions, Tail Recursion   slides: pptx   pdf   pdf6up   code: sml 
    Tail recursion moved to Jan 23 after the Jan 21 holiday
  12.  
  13. Unit 3: First-Class Functions and Closures    Reading Notes    Videos
  14.   L7. Jan 23: First-Class Functions   slides: pptx   pdf   pdf6up   code: sml
  15.   S3. Jan 24: Standard-Library Docs, Unnecessary Function Wrapping, Map, & More   slides: pdf   pdf4up   code:sec3.sml   higher-order.sml
  16.   L8. Jan 25: Lexical Scope and Function Closures   slides: pptx   pdf   pdf6up   code: sml
  17.   L9. Jan 28: Function-Closure Idioms   slides: pptx   pdf   pdf6up   code: sml
  18.  
  19. Unit 4: ML Modules, Type Inference, Equivalence, & More    Reading Notes    Videos
  20.   L10. Jan 30: ML Modules   slides: pptx   pdf   pdf6up   code: sml
  21.   S4. Jan 31: Mutual Recursion, More Currying, More Modules   slides:   pptx   pdf   code:   all_pairs.sml   bank.sml  mutual_rec.sml
  22.   L11. Feb 1: Type Inference   slides: pptx   pdf   pdf6up   code: sml
  23.   L12. Feb 4: Equivalence   slides: pptx   pdf   pdf6up
  24.  
  25. Course-Motivation Interlude, Feb 4-6  slides  pdf  pdf6up   Videos
  26.  
  27. Unit 5: Racket, Delaying Evaluation, Memoization, Macros    Reading Notes    Videos
  28.   L13. Feb 6-11: Racket Introduction   slides: pptx   pdf   pdf6up   code: rkt
  29.   S5. Feb 7 <Midterm Review for Midterm on Feb 8>
  30.   L14. Feb 13: Thunks, Laziness, Streams, Memoization   slides: pptx   pdf   pdf6up   code: rkt
    Some of the material in L14 is covered in S6 instead
  31.   S6. Feb 14: More streams, memoization, etc.   slides: pdf   pdf6up   code: sec6.rkt   streams.rkt
  32.   L15. Feb 15: Macros   slides: pptx   pdf   pdf6up   code: rkt
  33.  
  34. Unit 6: Structs, Implementing Languages, Static vs. Dynamic Typing    Reading Notes    Videos
  35.   L16. Feb 15-20: Datatype-Style Programming With Lists or Structs   slides: pptx   pdf   pdf6up   code: rkt   sml
  36.   L17. Feb 20-22: Implementing Languages Including Closures   slides: pptx   pdf   pdf6up   code: rkt
    Some of the material in L17 is covered in S7 instead
  37.   S7. Legal ASTs, Macros as Functions, and More   slides: pdf
  38.   L18. Feb 22-25: Static vs. Dynamic Typing   slides: pptx   pdf   pdf6up   code: rkt   sml
  39.  
  40. Unit 7: Ruby, Object-Oriented Programming, Subclassing    Reading Notes    Videos
  41.   L19. Feb 27: Introduction to Ruby and OOP   slides: pptx   pdf   pdf6up   code: lec19_silly.rb   lec19_example.rb
  42.   S8. Ruby arrays, hashes, ranges, blocks, and more slides   (See also material posted with L20.)
    Some of the material in L20 is covered in S8 instead
  43.   L20. Mar 1-4: Arrays & Such, Blocks & Procs, Inheritance & Overriding   slides: pptx   pdf   pdf6up   code: rb
  44.   L21. Mar 4-6: Dynamic Dispatch Precisely, and Manually in Racket   slides: pptx   pdf   pdf6up   code: rb   sml   rkt
  45.  
  46. Unit 8: Program Decomposition, Mixins, Subtyping, and More    Reading Notes    Videos
  47.   L22. Mar 6-8: OOP vs. Functional Decomposition; Adding Operators & Variants; Double-Dispatch 
       slides: pptx   pdf   pdf6up   code stage A:   sml   rb   java   code stage B:   sml   rb   java   code stage C:   sml   rb   java
  48.   S9. Mar 7: Double-Dispatch, Expression Problem, Mixins, and Visitors   slides: pdf   pdf6up   code: janken.rb  janken.sml   helpers.sml   mixins.rb   visitor.rb   visitor.sml
  49.   L23. Mar 8: Multiple Inheritance, Mixins, Interfaces, Abstract Methods   slides: pptx   pdf   pdf6up   code: rb
  50.   L24. Mar 11-13: Subtyping   slides: pptx   pdf   pdf6up
  51.   L25. Mar 13: Subtyping for OOP; Comparing/Combining Generics and Subtyping   slides: pptx   pdf   pdf6up
  52.   S10. Mar 14: Review, Especially Subtyping   slides: pdf   counter-examples
  53.  
  54. L26. Mar 15: Course Victory Lap   slides: pptx   pdf   pdf6up