Few Things on Scala - Speaker Deck

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Few things on Scala ͍ΒͪͷͨΊͷ4DBMBೖ໳ Image: typesafe.com Sorami Hisamoto 09 July 2013 @ PG

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For me to digest, and to introduce some of the contents from l'VODUJPOBM1SPHSBNNJOH1SJODJQMFTJO4DBMBz a marvelous course by Martin Odersky (plus alpha).

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For me to digest, and to introduce some of the contents from l'VODUJPOBM1SPHSBNNJOH1SJODJQMFTJO4DBMBz a marvelous course by Martin Odersky (plus alpha). https://www.coursera.org/course/progfun

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For me to digest, and to introduce some of the contents from l'VODUJPOBM1SPHSBNNJOH1SJODJQMFTJO4DBMBz a marvelous course by Martin Odersky (plus alpha). https://www.coursera.org/course/progfun Disclaimar I’m just a novice. Watch the lectures by yourself!

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“Scala is so cool that nobody knows it.” Image: - Cal Henderson http://www.youtube.com/watch?v=i6Fr65PFqfk

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“I call Scala an old wine in a new bottle.” Image: - Venkat Subramaniam http://www.youtube.com/watch?v=LH75sJAR0hc

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Image: Programming Paradigms

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Image: Programming Paradigms ‣ Imperative ໋ྩܕ ‣ Functional ؔ਺ܕ ‣ Logic ࿦ཧϓϩάϥϛϯά 

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Image: Programming Paradigms ‣ Imperative ໋ྩܕ ‣ Functional ؔ਺ܕ ‣ Logic ࿦ཧϓϩάϥϛϯά  Orthogonal to Object Oriented Programming.

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Image: ij There's a strong correspondence between Imperative Programs and Computers. Memory cells, load/store instructions, etc...

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Image: ij There's a strong correspondence between Imperative Programs and Computers. Memory cells, load/store instructions, etc... Pure imperative programming   is limited by the "Von Neumann" bottleneck.

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Image: How can we avoid conceptualizing programs word by word?

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Image: How can we avoid conceptualizing programs word by word? High-level abstractions: ideally, develop theories of collections, shapes, strings, ...

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Image: How can we avoid conceptualizing programs word by word? High-level abstractions: ideally, develop theories of collections, shapes, strings, ... Let’s concentrate on deﬁning theories for operators   expressed as functions.

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Image: Theory: data types & operations. Normally, a theory does not describe mutations.

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Image: Theory: data types & operations. Normally, a theory does not describe mutations. e.g. (a*x + b) + (c*x + d) = (a+c)*x + (b+d)

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Image: Functional Programming Restricted sense: programming without mutable variables, assignments, loops, and other imperative control structures. Wider sense: Focusing on the functions.

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Image: ‣ Assignment-less 

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Image: Don't need to worry about thread safety. ‣ Assignment-less 

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Image: Don't need to worry about thread safety. ‣ No side effects  ‣ Assignment-less 

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Image: Don't need to worry about thread safety. ‣ No side effects  Multiple calls.   Support concurrency. ‣ Assignment-less 

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Image: Don't need to worry about thread safety. ‣ No side effects  ‣ Referential transparency  Multiple calls.   Support concurrency. ‣ Assignment-less 

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Image: Don't need to worry about thread safety. ‣ No side effects  ‣ Referential transparency  Multiple calls.   Support concurrency. Can move code up n' down.   Can distribute to multicore. ‣ Assignment-less 

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Why it matters? Image:

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Why it matters? Brevity. Easier to debug. Concurrency. Image:

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Image: ‣ 1959 Lisp ‣ 1975-77 ML, FP, Scheme ‣ 1978 Smalltalk ‣ 1986 Standard ML ‣ 1990 Haskell, Earlang ‣ 1999 XSLT ‣ 2000 OCaml ‣ 2003 Scala, XQuery ‣ 2005 F# ‣ 2007 Clojure

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Image: http://upload.wikimedia.org/wikipedia/commons/8/85/Scala_logo.png

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‣ Includes full support of functional programming.  Currying, pattern matching, lazy evaluation, tail recursion, immutability, etc. ‣ Static typing.  “In Java, when they said typing they meant your ﬁngers.”  “You type less, because it is more typed.   In a language that is typed less, you type more.”  - V. Subramaniam http://www.youtube.com/watch?v=LH75sJAR0hc Image: OO + FP

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Image: Image: Used in Twitter, LinkedIn, Foursquare, Sony, Amazon, Facebook, NASA, ...

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“ ... if someone had shown me the Programming in Scala book [...] back in 2003 I'd probably have never created Groovy. ” - James Strachan, the creator of Groovy  http://macstrac.blogspot.jp/2009/04/  scala-as-long-term-replacement-for.html

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“ No other language on the JVM seems as capable of being a ‘replacement of Java’ as Scala, and the momentum behind Scala is now unquestionable. ” - Charles Nutter, the lead developer of JRuby http://blog.headius.com/2009/04/future-part-one.html

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“ If I were to pick a language to use today other than Java, it would be Scala. ” - James Gosling, the father of Java Image:

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Sounds good, but it is also ... Image:

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Sounds good, but it is also ... a complex language. a ‘kitchen sink language’. Image:

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“ The most depressing thing on Scala is [...] most people pick up Scala as ‘Java with more concise syntax’. ”  - James Gosling https://twitter.com/akarazniewicz/status/11353944609521664

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Anyway, let’s get started. Image:

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Image: “Tool Setup” page in Odersky’s course page.  https://class.coursera.org/progfun-002/wiki/view?page=ToolsSetup 

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On IDEs,“worksheet” might be helpful. Image:

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On IDEs,“worksheet” might be helpful. Image:

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giter8 A command line tool to apply templates deﬁned on github. https://github.com/n8han/giter8 sbt A build tool. http://www.scala-sbt.org/ Image:

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Image: Natural Language Processing & Machine Learning?

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Image: Scalala - developed by Daniel Ramage,   who used to be under Chris Manning. Natural Language Processing & Machine Learning?

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Image: Scalala - developed by Daniel Ramage,   who used to be under Chris Manning. Other libraries: Breeze, OptiML, FACTORIE, and more. Natural Language Processing & Machine Learning?

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Image: Scalala - developed by Daniel Ramage,   who used to be under Chris Manning. Other libraries: Breeze, OptiML, FACTORIE, and more. “Scala and Machine Learning with Andrew McCallum”  http://www.youtube.com/watch?v=DkRLTToCw-0 NAACL2013 “Tagger in 2hrs” paper - implementation in Scala.  https://github.com/dhgarrette/low-resource-pos-tagging-2013 Natural Language Processing & Machine Learning?

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Some Examples Image:

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First, some brevity. Image:

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You can drop the things that are obvious.

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ɾ ɾ ɾ

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“for” is powerful in Scala. (For more usage, refer to “Programming in Scala” Chapter 7.) ɾ ɾ ɾ

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Square roots with Newton's method Image:

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‣ To compute sqrt(x), ‣ Start with initial estimate y (say, 1). ‣ Repeatedly improve the estimate   by taking the mean of y and x/y. Image:

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Iterate until the guess is   good enough.

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Iterate until the guess is   good enough. Improve the guess  by taking mean of  x and guess.

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Image: Currying

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Note that a and b are unchanged.

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Note that a and b are unchanged.

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Note that a and b are unchanged. These are special cases of for different values of f .

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Note that a and b are unchanged. These are special cases of for different values of f . Can we factor out the common pattern?

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higher order function

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higher order function

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higher order function Or even better ...

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higher order function Or even better ...

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higher order function Or even better ... anonymous functions

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Function returning function.

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Function returning function.

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Function returning function.

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Function returning function.

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Function returning function.

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Function returning function. Currying Transforming a function that takes multiple arguments in such a way that it can be called as a chain of functions, each with a single argument.

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Finding Fixed Points Image:

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Image: Number x is called a ﬁxed point of a function f if f(x) = x.

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Image: Number x is called a ﬁxed point of a function f if f(x) = x. For some f, we can locate the ﬁxed points by repetitive way: x, f(x), f(f(x)), f(f(f(x))), ... until the value does not vary anymore.

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Image: Now, sqrt(x) = y such that y*y = x .

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Image: Now, sqrt(x) = y such that y*y = x . Or, sqrt(x) = y such that y = x /y .

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Image: Now, sqrt(x) = y such that y*y = x . Or, sqrt(x) = y such that y = x /y . Consequently, sqrt(x) is a ﬁxed point of y → x /y .

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Controls the oscillation.

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Rational Numbers ༗ཧ਺ Image:

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Class

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Method

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Method

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... and other things

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Operators

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Operators Relaxed identiﬁers.

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Operators Relaxed identiﬁers.

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Operators Relaxed identiﬁers. Precedence rules, just like the maths.

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Image: Binary Tree ೋ෼໦

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Image: (Time’s up)

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Image: (Time’s up) See Coursera week 3 https://class.coursera.org/progfun-002/lecture/index - Class hierarchies - Polymorphism, etc.

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Some references for further study Image:

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“Why Scala?” Epic. Just watch it.  Venkat Subramaniam. www.youtube.com/watch?v=LH75sJAR0hc  Image: “Functional Programming Principles in Scala” A bliss online course.  Martin Odersky. www.coursera.org/course/progfun  Programming in Scala” The Bible, by the creator himself.  Martin Odersky, Lex Spoon, & Bill Venners.  Programming Scala” An O’Reilly book. First part publicly available online.  Dean Wampler & Alex Payne. shop.oreilly.com/product/9780596155964.do  “Pragmatic Real-World Scala” A nice overview presentation by Typesafe CTO.  Jonas Bonér. www.slideshare.net/jboner/

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Image: END. Tanoshii desu kara