The Evolution of Scala / Scala進化論

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The Evolution Of Scala
Martin Odersky
EPFL and Typesafe
Scala 進化論

10 Years of Scala
Scala も今年で 10才。

Pre History
1980s Modula-2, Oberon
1990-95 Functional Programming
1995-98 Pizza
1998-99 GJ, javac
2000-02 Functional ...

4
Minimal programming language based on type members and functional nets (a variant of join calculus)
Analogous to Pict ...

A Minimal Language
•Idea of Funnel: Show that we can build a general programming language that can be understood as thin ...

Motivation for Scala
•Grew out of Funnel
•Wanted to show that we can do a practical combination of OOP and FP.
•What go...

Why a New Language?
•The OO dogma ruled then: Encapsulate mutable data with methods.
–Infamous example: Java beans.
–Th...

8
Really, Why a new Language?
The work on Scala was motivated by two hypotheses:
Hypothesis 1: A general-purpose langua...

How That Worked Out
9
(from:James Iry: A Brief, Incomplete, and Mostly Wrong History of Programming Languages)
「OO、FP両陣...

Scala and Pizza
•Pizza (Odersky and Wadler 96) was another language on the JVM that added functional elements to Java:
–...

Java Features Not kept in Scala
public
static
void
Enumerations
Annotation Syntax
Wildcard types
Raw types
Primiti...

Scala Beginnings
2003: First internal use
–to teach “Functional and Logic Programming Course” at EPFL. (2nd year, ~ 150 ...

Scala Reloaded
2006: Scala 2.0 released
–Compiler written in Scala
–Followed the cake-pattern described “Scalable Compo...

Scala Reloaded
2006: Scala 2.0 released
–Compiler written in Scala
–Followed the cake-pattern described “Scalable Compo...

Learning from Experience
Scala 1.x had
–Parameterless methods supporting the uniform access principle.
def length: Int ...

Avoiding the Pitfalls
1.Auto-add () for references f is to nullary functions
def f() = ...
2.Eta-expand only if
–expec...

The Growth Year
2007: Scala 2.3-2.7 add lots of new features:
Extractors object Email { def unapply ... } case Email(nam...

Why The Rapid Growth?
•People asked for it
–“If Scala only had this one new feature, I could use it in my organization” ...

Community Formation
2007: Lift web framework launched.
2008: First Scala liftoff unconference (50 particants)
–Twitter ...

Scala 2.8 and 2.9: Consolidation
2010: Scala 2.8, with
–New collections with bitrot prevention.
–Fixed leaky array mode...

Scala 2.10: Differentiation
2012: Scala 2.10, with
•New features, added through the Scala Improvement Process (SIPs):
–...

Features Controlled by SIP-18
From language:
–Implicit Conversions
–Dynamic
–Postfix Operators
–Dynamic dispatch on s...

Now: Scala 2.11
•Smaller:
–broke out parts of libraries into separate modules
•Faster
–Better incremental compilation ...

Now: Scala.JS
Why a Scala for Javascript?
–JS is becoming ubiquitous.
–Desire to use the same language on client and se...

Invariants
In all this evolution, what stays constant?
What are some of the essential traits that make Scala what it is?...

1st Invariant: A Scalable Language
•Instead of providing lots of features in the language, have the right abstractions so...

Libraries on top of Scala
27
SBT
Chisel
Spark
Spray
Kafka
Akka
ScalaTest
Squeryl
Specs
shapeless
Scalaz
Slick...

$Growable = Good? In fact, it’s a double edged sword. –DSLs can fracture the user community (“The Lisp curse”) –Besides,...$

•Scala’s core is its type system.
•Most of the advanced types concepts are about flexibility, less so about safety.
2nd ...

Stunted Evolution
null - “The Million Dollar Mistake”
•Why does Scala not have null-safety?
•We had plans to do it
you...

What’s Next?
•Scala 2.12 will be a fairly conservative evolution of 2.11
•Main feature: Java 8 interop.
–Scala and Java...

And After That?
Main Goals: Make the language and its libraries
•simpler to understand,
•more robust,
•better performi...

Scala “Aida”
Will concentrate on the standard library.
–Reduce reliance on inheritance
–Make all default collections im...

Scala “Don Giovanni”
Concentrates on the language
•Simple foundations:
–A single fundamental concept - type members – c...

Scala “Don Giovanni”
•Removing puzzlers:
–Result types mandatory for implicit definitions.
–Inherited explicit result t...

The Growth Year, Revisited
Extractors object Email { def unapply ... } ✔ case Email(name, domain) => ...
Tuples (1, “a”,...

Conclusion
•Languages are not cast in stone; they evolve whether you like it or not.
•Community matters
•Community will...

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