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Know Your Types
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Michael Bernstein
June 21, 2014
Technology
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Know Your Types
GoRuCo 2014
Michael Bernstein
June 21, 2014
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Transcript
Know Your Types Michael R. Bernstein June 2014 Gotham Ruby
Conference, NYC w michaelrbernste.in t @mrb_bk
I’m Obsessed
None
What Are Types?
“What we talk about when we talk about types” Benton,
2014
“We don't talk about types, we argue about them.”
“Type Systems” Cardelli, 1996
None
Computer Science Skill 0 25 50 75 100 Homepage Design
Outdatedness Computer Science Skill vs. Homepage Design Outdatedness
Computer Science Skill 0 25 50 75 100 Homepage Design
Outdatedness Bernstein’s Law
“A collection of values. An estimate of the collection of
values that a program fragment can assume during program execution.” Type
int bool string int -> bool
“A component of a type system. A rule stating the
conditions under which a particular program construct will not cause forbidden errors.” Type Rule
None
“A collection of type rules for a typed programming language.
Same as static type system.” Type System
None
“A language where good behavior is determined before execution.” Statically
checked language
“A language where good behavior is enforced during execution.” Dynamically
checked language
“The process of checking a program before execution to establish
its compliance with a given type system and therefore to prevent the occurrence of forbidden errors.” Typechecking
“The process of finding a type for a program within
a given type system.” Type Inference
How Can Types Help Us?
“Propositions as Types” Wadler, 2014
None
None
Isomorphism
iso morph
equal shape
Propositions are Types
None
Proofs are Programs
Normalization of proofs is evaluation of programs
None
None
None
None
None
Deep Understanding
Mathematical Certainty
Enlightenment
“Types and Programming Languages” a.k.a ‘TAPL’ Pierce, 2002
Detecting Errors
Abstraction
Documentation
Safety
So Much More!
Types and Ruby (But Really Dynamic Languages in General)
“A Practical Optional Type System for Clojure” Bonnaire-Sergeant,2012
None
“Typed Scheme: From Scripts to Programs” Tobin-Hochstadt, 2010
“Gradual Typing for Functional Languages” Siek & Taha, 2006
Gradual Typing
“…safe interoperability between typed and untyped portions of a single
program” ! - Sam Tobin-Hochstadt
“Dynamic Inference of Static Types for Ruby” An, Chaudhuri, Foster,
Hicks, 2011
“…constraint-based dynamic type inference, a technique that infers static types
based on dynamic program executions.”
None
“The Ruby Type Checker” Ren, Toman, Strickland, Foster 2013
“RTC is designed so programmers can control exactly where type
checking occurs: type-annotated objects serve as the “roots” of the type checking process, and unan- notated objects are not type checked.”
None
Challenges
“Experience from Developing the Dialyzer: A Static Analysis Tool Detecting
Defects in Erlang Applications” Sagonas, 2005
“…testing, no matter how thorough, cannot of course detect all
software defects. Tools that complement testing, such as static analyzers, have their place in software development regardless of language.”
Conclusions
Types and Type Systems Are Really, Really Cool
Types Are A Prism
A Type System Can Be A Guide
Let’s Push It Forward
Thank You w michaelrbernste.in t @mrb_bk