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Teaching Clojure
André Willik Valenti
TheConf | São Paulo-SP | Brazil
August 16th 2019
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Disclamer
This presentation reflects the author's opinions.
It does not necessarily reflect employers' opinions.
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Introduction
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André Willik Valenti
● Academic-industrial background
○ BSc. and MSc. in Computer Science
○ Developer for ~5 years
○ Professor for ~5 years
● Experiences in private and public sectors
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André Willik Valenti
● Familiar languages:
○ Java
○ JavaScript/NodeJS/CoffeeScript
○ HTML, CSS
○ Ruby, Python
○ C#, Lua, PHP, C++, Haskell, ML
○ Clojure
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IFSP
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IFSP
● Federal Institute for Education, Science and Technology of
São Paulo State
● Public teaching institution
● Secondary and tertiary education
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https://www.ifsp.edu.br/sobre-o-campus
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IFSP
● 110-year-old institution
○ 1909: Escola de Aprendizes Artífices
○ 1970: Escola Técnica Federal
○ 1990: CEFET - Centro Federal de Educação Tecnológica
○ 2008: IFSP
● Professor there since 2013
○ 2013 - 2014: São Carlos
○ 2014 - 2019: Campinas
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● Programming Languages, OOP
○ C#, Java
● Game Development
○ JavaScript, Lua
● Web Development
○ HTML, CSS, JavaScript
○ Java, PHP, NodeJS
● Other
○ Python, Agile Methodologies, OS
Regular subjects I've taught
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● 2013: TDD - Test-Driven Development
● 2017: Basic Chess
● 2019: Introduction to FP with Clojure
Extension courses I've applied
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What's an extension course? What's extension?
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Extension
● Teaching, research and extension
○ Pillars of universities and similar institutions in Brazil
● Actions that interest and involve the external community
○ Courses
○ Lectures
○ Events
○ Shows
○ …
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Some extension courses at IFSP Campinas
● Data Science and Artificial Intelligence
● Android Development
● Geoprocessing
● Oracle Databases
● Computing for senior citizens
● …
(https://www2.cmp.ifsp.edu.br/extensao/portfolio.php)
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Why a Functional Programming/Clojure course?
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Motivation
● Audience in Campinas
○ Technology research and software development center
● Functional programming is everywhere
○ …except in colleges curricula
● Clojure is becoming widespread
○ Has job offerings
○ Fits well an ongoing Java project
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Clojure
● Lisp dialect
● Dynamically typed
● Created by Rich Hickey
● Released on 2007
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Clojure
● More pragmatic than philosophical
○ "Getting stuff done" over "following principles"
● Favors immutability
○ ...but does not enforce it
● Favors idiomatic constructs
○ ...but allows everything else (e.g., Java interop)
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What does Clojure code look like?
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(defn to-text
[game-data]
(->> game-data
to-char-matrix
(reduce (fn [ret row-data]
(str ret
(reduce #(str %1 %2 \game-data) "" row-data)
\newline))
"")))
(defn to-json
[game-data]
{:id (game-data :id)
:board (for [row-data (to-char-matrix game-data)]
(reduce str row-data))})
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Course history
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Oct. 2018 Hi, I'm Clojure!
Great ideas
and tools here.
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Oct. 2018
Cool!
I should learn
that stuff…
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(make-extension-course! :clojure 2019)
1. Wait for call for proposals
2. Submit proposal
3. Make requested changes
4. Hope for approval
5. Apply course
6. Bob's your uncle!
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Oct. 2018: Call for proposals
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Nov. 2018: Proposal elaboration
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Nov. 2018: Proposal elaboration
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● Campinas campus
○ Acceptance of proposal on late Nov.
● Vice-Rectory of Extension
○ Acceptance expected for late Jan.
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Dec. 2018 - Jan. 2019: Promotion
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● IFSP website
● E-mail
● Physical A4 posters
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Feb. 2019
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● Acceptance of proposal by Vice-Rectory of Extension
● Course started of Feb. 12th
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In numbers
● 51 registered (inscritos)
● 22 enrolled (matriculados)
● 16 present after first month
● 9 finished
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In numbers
Of those 16 present after first month...
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In numbers
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Current IFSP students 3
Former IFSP students 5
Colleagues of former 6
UNICAMP students 4
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How many people...
...came because of the poster or the QR Code?
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Marketing
matters
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Lesson learned #1
You gotta sow a lotta
seeds, on proper soil.
Remember the
Conversion Funnel!
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Learning Clojure
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2011
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http://learnyouahaskell.com/
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2014
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https://www.coursera.org/learn/programming-languages
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2019
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https://www.clojure.org/guides/learn/syntax
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2019
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REPL (lein repl)
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2019
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https://learnxinyminutes.com
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● Quick, concrete overview:
○ https://learnxinyminutes.com
● Explanations and exercises:
○ https://clojure.org/guides/learn/syntax
● Quick playground:
○ https://repl.it/languages/clojure
How I recommend starting to learn Clojure
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● Local environment:
○ Leiningen (https://leiningen.org/)
○ VSCode (https://code.visualstudio.com) with extensions
How I recommend starting to learn Clojure
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Commands to install VSCode extensions
code --install-extension avli.clojure
code --install-extension tonsky.clojure-warrior
code --install-extension leocardoso94.clojure-snippets
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Course overview
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● 30 hours
● 18 weeks
● Tuesdays, 7:00 - 8:40 PM (classroom)
Course load
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● Functions, immutability
● Lists, recursion
● Clojure syntax
● Tools, libraries
● Mutability
● Project structuring
● Records, macros and parallelism
● Project presentation
Curriculum
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1. Functional programming concepts (with JavaScript)
2. Clojure introduction
3. Project development
Structure
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1. Functional programming concepts (with JavaScript)
○ Functions, values
○ Immutability, side-effects, purity
○ Recursion, tail-recursion
Structure
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2. Clojure introduction
○ Prefix notation, functions, variables
○ Conditionals, recursion
○ vector, list, set, map
Structure
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3. Project development
○ Leiningen
○ Ring (web framework)
○ Atoms, mutability
Structure
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Course application
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Sample exercises
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Immutability
Which of these are pure functions?
1. x => console.log(x)
2. (f, l) => ({ firstName: f, lastName: l })
3. array => array.length + 1
4. array => ++array.length
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Standard functions
Write your own version of a map function.
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Functions as arguments and result
Write a function that generates a multiplier function.
function generate(…) {
return …
}
const triple = generate(3);
triple(10); // 30
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Recursion
What does this function do?
function a(i, j) {
if (i < j) {
return i + a(i + 1, j);
} else {
return i;
}
}
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Recursion
What does this function do?
const c = (i, j) => i < j ? i + c(i + 1, j) : i;
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Prefix notation
Write these expressions in Clojure:
1. (tf - 32) / 1.8
2. 1.8tc + 32
3. (-b + sqrt(b² - 4ac)) / 2a
4. (-b - sqrt(b² - 4ac)) / 2a
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Conditionals
Make a tail-recursive factorial function in Clojure.
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Libraries; web development
Let's do a dojo using Ring and Compojure!!
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Project
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Project
● Groups of 2 students
● Choose one theme among many
● Develop a simple application
● Present it in 10 ~ 15 minutes
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● Action game
● Compiler
● Data processing
● Video and/or audio processing
● Web scraping
● E-commerce front-end
● E-commerce back-end
● RESTful API
Available themes
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Surveys
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Week 3/18: Level of difficulty
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16 answers
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Week 6/18: Level of difficulty
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14 answers
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Week 9/18: Level of difficulty
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15 answers
100%
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Week 3/18: Examples/exercises being in JavaScript
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16 answers
100%
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Week 6/18: How do you prefer studying Clojure?
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57%
43%
14 answers
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Week 13/18: About the coding dojo last class
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80%
10%
10%
10 answers
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Week 16/18: "The course was ____ my expectation"
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8 answers
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Week 18/18: informal survey
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Stundents found it nice
● REPL
● Standard data structures
● Tools, esp. Leiningen
● Ring middlewares
● Using vectors to store pairs
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Stundents found it difficult
● Find the parenthesis to close
● Error messages
● Tail-recursion
● Chaining functions
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Simple? Easy? https://www.infoq.com/presentations/Simple-Made-Easy/
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When developing a real system...
● Prefer simple design and implementation
○ …not necessarily easy ones
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But, when teaching an introductory course...
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Prefer the
easiest
stuff
(not necessarily the
simplest)
function(x) {
return x * 2;
}
instead of
x => x * 2
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Lesson learned #2
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Clojure impressions
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Parentheses
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● Not that hard
● You get used to them
● Do use a rainbow parentheses plugin
● Better yet, use quickie
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Pros
● Documentation
● Built-in data structures
● Automated testing
● Fun to learn and use
● "Finally free!" feeling
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Cons
● Complex
● Many ways to do everything
● Awful error messages
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Pro: automated testing
(ns sample-project.core-test
(:require [clojure.test :refer :all]
[sample-project.core :refer :all]))
(deftest a-test
(testing "FIXME, I fail."
(is (= 0 1))))
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Pro: automated testing
(ns sample-project.core-test
(:require [clojure.test :refer :all]
[sample-project.core :refer :all]))
(deftest a-test
(testing "Are a's equal to b's?"
(are [a b] (= a b)
1 1
2 2
3 3)))
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Con: many ways to do same thing
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Suppose you want to transform
{:a 1 :b {:c 2}}
into
{:a 1 :b {:c 3}}
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Con: many ways to do same thing
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Suppose you have it in a variable m
(def m {:a 1 :b {:c 2}})
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Con: many ways to do same thing
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Some ways to do it:
1. {:a (:a m) :b {:c (inc (:c (:b m)))}}
2. (assoc m :b {:c (inc (:c (:b m)))})
3. (assoc-in m [:b :c] (inc (get-in m [:b :c])))
4. (update-in m [:b :c] inc)
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Con: error messages
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Punishment!
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Pranks (pegadinhas)
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Pranks (pegadinhas)
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● conj
○ Inserts at beginning for lists, at end for vectors
● contains?
○ Checks element for sets, checks index for vectors
● clojure.set/intersection
○ Only works for sets
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def: innocuous?
(def a 10)
(defn f [] (+ 1 a))
(f) ; 11
(def a 20)
(f) ; ???
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def: innocuous?
(def a 10)
(defn f [] (+ 1 a))
(f) ; 11
(def a 20)
(f) ; 21!!!!!
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def: innocuous?
● def creates a Var
● Var's are mutable!!
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def: innocuous?
(with-redefs [a 30] (f)) ; 31
(f) ; 21
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def: innocuous?
● Use def carefully
● Prefer let whenever possible
● For private functions, use defn-
○ visible only inside namespace
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"No syntax"
' " @ # % & ( ) \ [ ] { } ^ ` ; : / . #{} -> ->> ~@
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References
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Great Rich Hickey talks
● The Value of Values
○ https://www.youtube.com/watch?v=-6BsiVyC1kM
● Simple Made Easy
○ https://www.infoq.com/presentations/Simple-Made-Easy/
○ Newer version: Simplicity Matters
● Effective Programs - 10 Years of Clojure
○ https://www.youtube.com/watch?v=2V1FtfBDsLU
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● slingshot
○ Enhanced exception handling (idiomatic)
● io.aviso/pretty
○ Pretty printing of unhandled exception (readable)
● quickie
○ Autorunning tests when file is saved (faster cycle)
Some useful Clojure tools
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http://tiny.cc/3dnl3y
Course material (in Portuguese)
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Conclusions
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What's functional programming all about?
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FP is
basically
about:
1. calculating next state
2. switching to it
Mutation only
happens on phase 2.
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Lesson learned #3
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Making hard easy
● Yes! You can bring novel knowledge to your workplace.
● Yes! You can make hard stuff easy for other people.
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Clojure is not...
● very welcoming (nasty error messages!)
● appropriate for new programmers (other Lisps might be)
● that hard, nor that easy
● simple!
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Clojure is...
● a great source of ideas and tools for software
development
● a production-ready ecosystem with a big community
● pragmatic!
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Things evolve
according to
people's needs
Lesson learned #4
Not always to the
original principles.
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I'm leaving IFSP...
● ...and joining Lambda3 next week
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Thank you! Questions?
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Contact:
● [email protected]
● https://twitter.com/awvalenti
● https://about.me/awvalenti