A gentle introduction to functional programming through

music and ClojureMødegruppe for F#unktionelle Københavnere, 24 November, 2015

Presented by Paul Lam

Agenda1. What is functional programming2. Setting up the environment3. Making some noise4. Making some music5. Transforming data to music6. Why functional programming

Wiki: Functional Programming

“In computer science, functional programming is a programming paradigm—a style of building the structure and elements of computer programs—that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data.”

Hello World

Clojure is a dynamic programming language that targets the Java Virtual Machine, Common Language Runtime, and JavaScript

Data LiteralsLong 42

BigInteger 12345678912345678912

Double 1.234

BigDecimal 1.234M

Ratio 22/7

String “fred”

Character \a \b \c

Keyword :a, :foo

Symbol fred, ethel

Boolean true, false

nil nil

Regex #”a*b”

Collection Types● Lists - singly linked, grow at front

○ (list 1 2 3), ‘(1 2 3), ‘(:fred "ethel" 27) ● Vectors - indexed access, grow at end

○ [1 2 :a :b], ["fred" :ethel 3/2]● Maps - key/value associations

○ {:a 1, :b 2, :c 3}, {1 "ethel" 2 "fred"}● Sets - collection with uniqueness constraint

○ #{:fred :ethel :lucy} ; duplicate key will error

● Heterogeneous● Everything Nests Arbitrarily!

○ [#{:a :b} "c" [:d] {1 :e 2 [:f :g]}]

Installing Leiningen

Go to http://leiningen.org/ and follow 4 steps(Note: You must have Java already installed)

1. Download the lein script (or on Windows lein.bat)2. Place it on your $PATH where your shell can find it (eg. ~/bin)3. Set it to be executable (chmod a+x ~/bin/lein)4. Run it (lein) and it will download the self-install package

Then run: $ lein repl // Start a Clojure REPL

Clojure Doc

● http://clojure.org/cheatsheet ● http://clojuredocs.org/● > (doc …)

Working with lists> (+ 1 2 3)6

> (first [1 2 3])1

> (rest [1 2 3])(2 3)

> (cons “x” [1 2 3])(“x” 1 2 3)

> (take 2 [ 1 2 3 4 5])(1 2)

> (drop 2 [1 2 3 4 5])(3 4 5)

> (range 10)(0 1 2 3 4 5 6 7 8 9)

> (filter odd? (range 10))(1 3 5 7 9)

> (map odd? (range 10))(false true false true false true false true false true)

> (reduce + (range 10))45

What is Overtone?

Overtone: “Collaborative Programmable Music”http://overtone.github.io/

Interface SuperCollider (an audio synthesis engine) using Clojurehttp://supercollider.sourceforge.net/

Workshoprepo -- https://github.com/Quantisan/functional-music

Working with Lists> (take 9 (cycle [1 2 3 4]))(1 2 3 4 1 2 3 4 1)

> (interleave [:a :b :c :d :e] [1 2 3 4 5])(:a 1 :b 2 :c 3 :d 4 :e 5)

> (partition 3 [1 2 3 4 5 6 7 8 9])((1 2 3) (4 5 6) (7 8 9))

> (map vector [:a :b :c :d :e] [1 2 3 4 5])([:a 1] [:b 2] [:c 3] [:d 4] [:e 5])

> (interpose \| "asdf")(\a \| \s \| \d \| \f)

> (apply str (interpose \| "asdf"))"a|s|d|f"

Working with Maps and Sets(def m {:a 1 :b 2 :c 3})

● (m :b) => 2 ● (:b m) => 2● (keys m) => (:a :b :c)● (assoc m :d 4 :c 42) => {:d 4, :a 1, :b 2, :c 42}● (merge-with + m {:a 2 :b 3}) => {:a 3, :b 5, :c 3}● (union #{:a :b :c} #{:c :d :e}) => #{:d :a :b :c :e}● (join #{{:a 1 :b 2 :c 3} {:a 1 :b 21 :c 42}} #{{:a 1 :b 2 :e 5} {:a 1 :b 21 :d 4}}) => #{{:d 4, :a 1, :b 21, :c 42} {:a 1, :b 2, :c 3, :e 5}}

Java Interop> (.toUpperCase "fred")"FRED"

> (.getName String)"java.lang.String"

> (System/getProperty "user.dir")"/Users/me/clojure/interop"

> Math/PI3.141592653589793

Java Interop> (map #(.getName %) (.getMethods java.util.Date))("equals" "toString" "hashCode" "clone" "compareTo" "compareTo" "parse" . . . <and many more>)

> (java.util.Date.)#inst "2015-01-26T21:49:01.403-00:00"

> (doto (java.util.Date.) (.setSeconds 33) (.setMinutes 22))#inst "2015-01-26T21:22:33.785-00:00"

https://github.com/Quantisan/functional-music/blob/solution/src/functional_music/tab.

clj

Solution

Drawbacks of FP

● requires thinking differently

● real-world programs are full of side-effects● difficulty predicting performance profile

Benefits of Functional Programming

● Easier to reason about● Composibility● Separation of concern

● Huges, “Why Functional Programming Matters”, 1990● http://weblog.raganwald.com/2007/03/why-why-functional-programming-matters.html

Contact

Paul Lam@Quantisanpaul@quantisan.com