Event Type Polymorphism Rex D. Fernando Robert Dyer Hridesh Rajan - - PowerPoint PPT Presentation

Event Type Polymorphism

Rex D. Fernando Robert Dyer Hridesh Rajan

Department of Computer Science Iowa State University {fernanre,rdyer,hridesh}@iastate.edu

This work was supported in part by NSF grant CCF-10-17334.

Overview Motivation Language Summary

◮ Motivation: Code re-use and specialization for event-based

separation of concerns

◮ Approach: Event Type Polymorphism in Ptolemy ◮ Technical Contributions:

◮ Formal semantics for event type polymorphism ◮ Simpler semantics, when compared to earlier work Rex D. Fernando, Robert Dyer and Hridesh Rajan 1 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

NumExp NumExp DivExp NumExp MultExp

AST

Rex D. Fernando, Robert Dyer and Hridesh Rajan 2 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

NumExp NumExp DivExp NumExp MultExp MultVisited

AST Events

C E class C announces event E

Rex D. Fernando, Robert Dyer and Hridesh Rajan 2 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

NumExp NumExp DivExp NumExp MultExp MultVisited DivVisited

AST Events

C E class C announces event E

Rex D. Fernando, Robert Dyer and Hridesh Rajan 2 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

NumExp NumExp DivExp NumExp MultExp MultVisited DivVisited NumVisited

AST Events

C E class C announces event E

Rex D. Fernando, Robert Dyer and Hridesh Rajan 2 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

NumExp NumExp DivExp NumExp MultExp MultVisited DivVisited NumVisited Tracing TypeCheck Evaluation

AST Handlers Events

C E class C announces event E H E event E's announcement invokes handler H

Rex D. Fernando, Robert Dyer and Hridesh Rajan 2 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

NumExp NumExp DivExp NumExp MultExp MultVisited DivVisited Tracing TypeCheck Evaluation NumVisited

AST Handlers Events

C E class C announces event E H E event E's announcement invokes handler H

Rex D. Fernando, Robert Dyer and Hridesh Rajan 2 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

NumExp NumExp DivExp NumExp MultExp MultVisited DivVisited Tracing TypeCheck Evaluation NumVisited

AST Events Handlers

C E class C announces event E H E event E's announcement invokes handler H

Rex D. Fernando, Robert Dyer and Hridesh Rajan 2 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

MultVisited <event> + node : MultExp + left : Exp + right : Exp DivVisited <event> + node : DivExp + left : Exp + right : Exp PlusVisited <event> + node : PlusExp + left : Exp + right : Exp

Rex D. Fernando, Robert Dyer and Hridesh Rajan 3 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

MultVisited <event> + node : MultExp + left : Exp + right : Exp DivVisited <event> + node : DivExp + left : Exp + right : Exp PlusVisited <event> + node : PlusExp + left : Exp + right : Exp

Rex D. Fernando, Robert Dyer and Hridesh Rajan 3 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

MultVisited <event> + node : MultExp + left : Exp + right : Exp DivVisited <event> + node : DivExp + left : Exp + right : Exp PlusVisited <event> + node : PlusExp + left : Exp + right : Exp

Rex D. Fernando, Robert Dyer and Hridesh Rajan 3 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

class ASTTracer { void printMult(MultVisited next) { logVisitBegin(next.node ().getClass ()); next.invoke (); logVisitEnd(next.node ().getClass ()); } when MultVisited do printMult; void printDiv(DivVisited next) { logVisitBegin(next.node ().getClass ()); next.invoke (); logVisitEnd(next.node ().getClass ()); } when DivVisited do printDiv; void printPlus(PlusVisited next) { logVisitBegin(next.node ().getClass ()); next.invoke (); logVisitEnd(next.node ().getClass ()); } when PlusVisited do printPlus; }

Rex D. Fernando, Robert Dyer and Hridesh Rajan 4 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

class ASTTracer { void printMult(MultVisited next) { logVisitBegin(next.node ().getClass ()); next.invoke (); logVisitEnd(next.node ().getClass ()); } when MultVisited do printMult; void printDiv(DivVisited next) { logVisitBegin(next.node ().getClass ()); next.invoke (); logVisitEnd(next.node ().getClass ()); } when DivVisited do printDiv; void printPlus(PlusVisited next) { logVisitBegin(next.node ().getClass ()); next.invoke (); logVisitEnd(next.node ().getClass ()); } when PlusVisited do printPlus; }

Rex D. Fernando, Robert Dyer and Hridesh Rajan 5 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

◮ Can we re-use code here? ◮ What happens if a new AST type is added? ◮ What happens if an AST type is removed?

Rex D. Fernando, Robert Dyer and Hridesh Rajan 6 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

◮ Can we re-use code here?

◮ No! Passing event closures (next) as argument is illegal.

(to simplify reasoning about invoke/proceed functionality)

◮ What happens if a new AST type is added? ◮ What happens if an AST type is removed?

Rex D. Fernando, Robert Dyer and Hridesh Rajan 6 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

◮ Can we re-use code here?

◮ No! Passing event closures (next) as argument is illegal.

(to simplify reasoning about invoke/proceed functionality)

◮ What happens if a new AST type is added?

◮ Must update all handlers to support that node type!

◮ What happens if an AST type is removed?

Rex D. Fernando, Robert Dyer and Hridesh Rajan 6 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

◮ Can we re-use code here?

◮ No! Passing event closures (next) as argument is illegal.

(to simplify reasoning about invoke/proceed functionality)

◮ What happens if a new AST type is added?

◮ Must update all handlers to support that node type!

◮ What happens if an AST type is removed?

◮ Must update all handlers and remove that node type! Rex D. Fernando, Robert Dyer and Hridesh Rajan 6 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

◮ Can we re-use code here?

◮ No! Passing event closures (next) as argument is illegal.

(to simplify reasoning about invoke/proceed functionality)

◮ What happens if a new AST type is added?

◮ Must update all handlers to support that node type!

◮ What happens if an AST type is removed?

◮ Must update all handlers and remove that node type!

Polymorphism can help us here!

Rex D. Fernando, Robert Dyer and Hridesh Rajan 6 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

MultVisited <event> + node : MultExp DivVisited <event> + node : DivExp PlusVisited <event> + node : PlusExp ExpVisited <event> + node : Exp BinArithVisited <event> + node : BinArith + left : Exp + right : Exp

Rex D. Fernando, Robert Dyer and Hridesh Rajan 7 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

MultVisited <event> + node : MultExp DivVisited <event> + node : DivExp PlusVisited <event> + node : PlusExp ExpVisited <event> + node : Exp BinArithVisited <event> + node : BinArith + left : Exp + right : Exp

Rex D. Fernando, Robert Dyer and Hridesh Rajan 7 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

MultVisited <event> + node : MultExp DivVisited <event> + node : DivExp PlusVisited <event> + node : PlusExp ExpVisited <event> + node : Exp BinArithVisited <event> + node : BinArith + left : Exp + right : Exp

Rex D. Fernando, Robert Dyer and Hridesh Rajan 7 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

class ASTTracer { void printExp(ExpVisited next) { logVisitBegin(next.node ().getClass ()); next.invoke (); logVisitEnd(next.node ().getClass ()); } when ExpVisited do printExp; }

Rex D. Fernando, Robert Dyer and Hridesh Rajan 8 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

class ASTTracer { void printExp(ExpVisited next) { logVisitBegin(next.node ().getClass ()); next.invoke (); logVisitEnd(next.node ().getClass ()); } when ExpVisited do printExp; }

◮ Quantifying over entire event hierarchy by only naming super

event!

◮ No need to update when a new AST type added! ◮ No need to update when an AST type removed!

Rex D. Fernando, Robert Dyer and Hridesh Rajan 8 Event Type Polymorphism

Overview Motivation Language Summary An Example - No Event Type Polymorphism Example Revisited - With Event Type Polymorphism

class ASTTracer { void printExp(ExpVisited next) { logVisitBegin(next.node ().getClass ()); next.invoke (); logVisitEnd(next.node ().getClass ()); } when ExpVisited do printExp; }

◮ Quantifying over entire event hierarchy by only naming super

event!

◮ No need to update when a new AST type added! ◮ No need to update when an AST type removed!

Let’s take a look at the language. . .

Rex D. Fernando, Robert Dyer and Hridesh Rajan 8 Event Type Polymorphism

Overview Motivation Language Summary Syntax Type-checking Rules Sub-event Relation Summary

decl ::= class c extends d { field* meth* binding* } | c event p extends q { form* } where c ∈ C, a set of class names d ∈ C ∪ {Object}, a set of superclass names p ∈ P, a set of event type names q ∈ P ∪ {Event}, a set of super event type names

Rex D. Fernando, Robert Dyer and Hridesh Rajan 9 Event Type Polymorphism

Overview Motivation Language Summary Syntax Type-checking Rules Sub-event Relation Summary

binding ::= when p do m e ::= register(e) | unregister(e) | announce p (e*) { e } | e.invoke() where m ∈ M, a set of method names

Rex D. Fernando, Robert Dyer and Hridesh Rajan 10 Event Type Polymorphism

Overview Motivation Language Summary Syntax Type-checking Rules Sub-event Relation Summary

(check event)

isClass(c) ∀i ∈ [1..n] :: isClass(ti) p ≪: q Π ⊢ c event p extends q {t1 var1, ..., tn varn} : OK

Rex D. Fernando, Robert Dyer and Hridesh Rajan 11 Event Type Polymorphism

Overview Motivation Language Summary Syntax Type-checking Rules Sub-event Relation Summary

(≪: Top)

isEvent(p) p ≪: Event

(≪: Reflexive)

isEvent(p) p ≪: p

(≪: Transitive)

isEvent(p) isEvent(q) isEvent(q′) p ≪: q′ q′ ≪: q p ≪: q

Rex D. Fernando, Robert Dyer and Hridesh Rajan 12 Event Type Polymorphism

Overview Motivation Language Summary Syntax Type-checking Rules Sub-event Relation Summary

(≪: Base)

(c event p extends q {t1 var1, ..., tn varn}) ∈ CT isEvent(q) [t′

1 var′ 1, ..., t′ m var′ m] = contextsOf (q)

∀i ∈ [1..n] :: ti vari ∈ [t1 var1, ..., tn varn] ⇒ (∃j ∈ [1..m] :: t′

j vari ∈ [t′ 1 var′ 1, ..., t′ m var′ m] ⇒ ti <: t′ j)

p ≪: q contextsOf recursively computes the list of all context for an event type q, based on its supertypes

Rex D. Fernando, Robert Dyer and Hridesh Rajan 13 Event Type Polymorphism

Overview Motivation Language Summary Syntax Type-checking Rules Sub-event Relation Summary

◮ New syntax: p extends q ◮ Typing rules use new relation: p ≪: q ◮ Both depth and width subtyping of context information

Rex D. Fernando, Robert Dyer and Hridesh Rajan 14 Event Type Polymorphism

Overview Motivation Language Summary

Related Work

◮ Implicit Invocation + Implicit Announcement [Steimann 2010]

◮ Implicit announcement allows ambiguity ◮ Harder to reason about what event(s) announced

◮ Escala [Gasiunas 2011]

◮ Does not support width subtyping ◮ Limits the ability to specialize sub-events Rex D. Fernando, Robert Dyer and Hridesh Rajan 15 Event Type Polymorphism

Overview Motivation Language Summary

Future Work

◮ Finish type-soundness proof (in Coq) ◮ Implement semantics in OpenJDK-based Ptolemy compiler

◮ Non-trivial to implement Rex D. Fernando, Robert Dyer and Hridesh Rajan 16 Event Type Polymorphism

Overview Motivation Language Summary

◮ Motivation: Code re-use and specialization for event-based

separation of concerns

◮ Ability to quantify over a hierarchy of events ◮ Allows for code re-use in event definitions and handlers ◮ Better maintenance - for both adding and removing events

◮ Approach: Event Type Polymorphism in Ptolemy

◮ Event types have inheritance ◮ Allow width and depth subtyping of context ◮ Handlers also handle sub-events

◮ Technical Contributions:

◮ Formal semantics for event type polymorphism ◮ Simpler semantics, when compared to earlier work Rex D. Fernando, Robert Dyer and Hridesh Rajan 17 Event Type Polymorphism

Questions?

http://ptolemy.cs.iastate.edu/

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

prog ::= decl* e decl ::= class c extends d { field* meth* binding* } | c event p extends q { form* } where c ∈ C, a set of class names d ∈ C ∪ {Object}, a set of superclass names p ∈ P, a set of event type names q ∈ P ∪ {Event}, a set of super event type names

Rex D. Fernando, Robert Dyer and Hridesh Rajan 18 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

t ::= c | thunk p field ::= c f meth ::= c m (form*) { e } form ::= t var, where var=this binding ::= when p do m where f ∈ F, a set of field names m ∈ M, a set of method names var ∈ {this} ∪ V, V is a set of variable names

Rex D. Fernando, Robert Dyer and Hridesh Rajan 19 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

ep ::= n | var | ep.f | ep != null | ep == ep | ep < ep | ! ep | ep && ep e ::= new c() | var | null | e.m(e*) | e.f | e.f = e | cast c e | form = e ; e | e ; e | if (ep) { e } else { e } | while (ep) { e } | register(e) | unregister(e) | announce p (e*) { e } | e.invoke() where n ∈ Z, the set of integers

Rex D. Fernando, Robert Dyer and Hridesh Rajan 20 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

(Concrete Type Inh.)

var′

i ∈ {var1, ..., varn}

concreteType(t′

i var′ i , [t1 var1, ..., tn varn]) = t′ i var′ i

(Concrete Type Depth)

∃j ∈ [1..n] :: tj var′

i ∈ [t1 var1, ..., tn varn]

concreteType(t′

i var′ i , [t1 var1, ..., tn varn]) = tj var′ i

Rex D. Fernando, Robert Dyer and Hridesh Rajan 21 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

(Top Context Vars)

contextsOf (Event) = •

(Context Vars)

(c event p extends q {t1 var1, ..., tn varn}) ∈ CT [t′

1 var′ 1, ..., t′ m var′ m] = contextsOf (q)

contextsOf (p) = [∀i ∈ [1..m] :: concreteType(t′

i var′ i , [t1 var1, ..., tn varn])]

+ [∀i ∈ [1..n] :: ti vari :: vari ∈ {var′

1, ..., var′ m})]

Rex D. Fernando, Robert Dyer and Hridesh Rajan 22 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

DivVisited <event> + node : DivExp ExpVisited <event> + node : Exp BinArithVisited <event> + node : BinArith + left : Exp + right : Exp contextsOf(ExpVisited) = [node:Exp] contextsOf(BinArithVisited) = [node:BinArith, left:Exp, right:Exp] contextsOf(DivVisited) = [node:DivExp, left:Exp, right:Exp]

Rex D. Fernando, Robert Dyer and Hridesh Rajan 23 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

(Is Event)

(c event p extends q {t1 var1, ..., tn varn}) ∈ CT isEvent(p)

Rex D. Fernando, Robert Dyer and Hridesh Rajan 24 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

(≪: Top)

isEvent(p) p ≪: Event

(≪: Refl.)

isEvent(p) p ≪: p

(≪: Trans.)

isEvent(p) isEvent(q) isEvent(q′) p ≪: q′ q′ ≪: q p ≪: q

Rex D. Fernando, Robert Dyer and Hridesh Rajan 25 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

(≪: Base)

(c event p extends q {t1 var1, ..., tn varn}) ∈ CT isEvent(q) [t′

1 var′ 1, ..., t′ m var′ m] = contextsOf (q)

∀i ∈ [1..n] :: ti vari ∈ [t1 var1, ..., tn varn] ⇒ (∃j ∈ [1..m] :: t′

j vari ∈ [t′ 1 var′ 1, ..., t′ m var′ m] ⇒ ti <: t′ j)

p ≪: q

Rex D. Fernando, Robert Dyer and Hridesh Rajan 26 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

θ ::= “type attributes” OK “program/top-level declaration” | OK in c “method, binding” | var t “var/formal/field” | exp t “expression” τ ::= c | ⊤ | ⊥ “class type expressions” π, Π ::= {I : θI}I∈K, “type environments” where K is finite, K ⊆ (L ∪ {this} ∪ V)

Rex D. Fernando, Robert Dyer and Hridesh Rajan 27 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

(check event)

isClass(c) ∀i ∈ [1..n] :: isClass(ti) p ≪: q Π ⊢ c event p extends q {t1 var1, ..., tn varn} : OK

Rex D. Fernando, Robert Dyer and Hridesh Rajan 28 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

(check binding)

isClass(c′) (c event p extends q {t1 var1, ..., tn varn}) ∈ CT c′ <: c (c′ m(thunk p var){e}) = methodBody(c, m) Π ⊢ when p do m : OK in c

Rex D. Fernando, Robert Dyer and Hridesh Rajan 29 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

(announce exp type)

(c event p extends q {t1 var1, ..., tn varn}) ∈ CT ∀i ∈ [1..n] :: Π ⊢ ei : exp ti Π ⊢ e : exp c′ c′ <: c Π ⊢ announce p(e1, . . . , en) {e} : exp c

Rex D. Fernando, Robert Dyer and Hridesh Rajan 30 Event Type Polymorphism

Appendix Full Syntax Auxilliary Methods Type-checking Rules Future Work

Implementation

◮ Static semantics are relatively simple ◮ But implementation is non-trivial

◮ Handling a supertype event requires the entire hierarchy rooted

by that event also be registered

◮ But to maintain separate compilation and type checking, event

types are only aware of their direct supertype

◮ What happens when loading new subtypes and handlers

already registered?

Rex D. Fernando, Robert Dyer and Hridesh Rajan 31 Event Type Polymorphism