PIL - A Platform Independent Language

PIL: A Platform Independent Language for Retargetable DSLs Zef Hemel, Eelco Visser Delft University of Techology, The Netherlands

domain-speciﬁc languages Stratego/XT

compiler

“traditional” compilers

“traditional” compilers ✘ low-level ✘ complex to generate ✘ machine-speciﬁc

DSL compilers

DSL compilers ✔ high-level ✔ easier to generate ✔ machine-independent

DSL generators ✔ high-level ✔ easier to generate ✔ machine-independent

software platforms

data model user interface logic access control workﬂow data validation

define page conference(c : Conference) { header { “Accepted papers” } list { for(p : Paper in c.papers where p.accepted) { listitem { output(p) } } } }

http://tweetview.net/ev/sle09

WebDSL compiler

java python

ANTLR perl 5 python objective-c action script c c# javascript c# 3 java delphi

perl 5 objective-c python action script c javascript java c# c# 3 delphi

ANTLR back-end support as of 4th of september 2009 language status Java in sync with ANTLR3 JavaScript in sync with ANTLR3 in sync with ANTLR3 (except no C# 3 support for -debug and -proﬁle) currently catching up with Objective-C release version last working version is v3.0ea7. Ruby Catching up with v3.0b3

DSL compiler architecture

DSL (text) parse DSL front-end (model) typecheck DSL (checked) desugar DSL (core) generate code Platform back-end pretty-print Code

retargeting a DSL compiler

DSL (core) Platform

DSL (core) Platform 1 Platform 2

DSL (core) large semantic gap Platform 1 Platform 2 front-end 25,000 back-ends 10,000 each

Java page-elem-to-java: |[ list { elem* } ]| -> |[ out.print(“<ul>”); stat_elem* out.print(“</ul>”); ]| with stat_elem* := <map(elem-to-java)> elem*

servlets

servlets ﬂexibility control performance

developer platform != code generator platform

developer platforms OOP Java C# Python Ruby

developer platforms dynamic typing lambda functions ORM framework event support ﬂexible syntax inner classes anonymous classes iterators annotations OOP Java C# Python Ruby

fancy platform features

Java page-elem-to-java: |[ list { elem* } ]| -> |[ out.print(“<ul>”); stat_elem* out.print(“</ul>”); ]| with stat_elem* := <map(elem-to-java)> elem*

Python page-elem-to-python: |[ list { elem* } ]| -> |[ out.print(“<ul>”) stat_elem* out.print(“</ul>”) ]| with stat_elem* := <map(elem-to-python)> elem*

language translation DSL (core) Platform 1 Platform 2

Microsoft™ Java™ language conversion assistant for Visual Studio™

Microsoft™ Java™ language conversion assistant for Visual Studio™ incomplete

DSL (core) C JRuby

compatibility

compatibility performance

compatibility performance maintenance

compatibility performance maintenance just for JVM and .NET

code generation OOP Java C# Python Ruby just subset of platforms

DSL (core) Platform 1 Platform 2 Platform n

DSL (core) IL Platform 1 Platform 2 Platform n

UNCOL Universal Computer Oriented Language Melvin E. Conway, 1958

C-- O-code UNCOL Universal Computer Oriented Language P-code Melvin E. Conway, 1958 gcc’s RTL

traditional ILs High-level IL machine software platform architecture low-level high-level familiar abstract syntax concrete syntax

abstract from platform familiar concrete syntax cheap to port easy DSL compiler integration platform interaction

PIL Platform Independent Language

DSL (core) PIL Java Python ...

abstract from platform familiar concrete syntax cheap to port easy DSL compiler integration platform interaction

✔ abstract from platform familiar concrete syntax cheap to port easy DSL compiler integration platform interaction

simplified Java ✘ visibility modifiers ✘ abstract classes ✘ interfaces ✘ inner/anonymous classes ✘ import com.somelib.*; ✘ checked exceptions ✘ primitive types ✘ one class per file ✘ static class members

a.b a = package, class, ﬁeld, variable?

PIL a::b a.b this.a.b

Java-like syntax class page::Home extends webdsl::web::Page { String title = null; String name = null; void init(pil::web::Request request) { this.name = request.getParameter(“name”); } void render(pil::util::PrintWriter out) { out.print(“<html><head><title>” + title + “</title></head><body>”); out.print(“<h1>Welcome “ + name + “</h1>”); out.print(“</body></html>”); } }

Object Bool Int Float Char Byte String MutableString Array<T> List<T> Set<T> Map<K,V> Exception

1,200 lines Stratego/platform

✔ abstract from platform familiar concrete syntax cheap to port easy DSL compiler integration platform interaction

✔ abstract from platform ✔ familiar concrete syntax cheap to port easy DSL compiler integration platform interaction

✔ abstract from platform ✔ familiar concrete syntax ✔ cheap to port easy DSL compiler integration platform interaction

Stratego/XT library imports libpil-front libpil-java-backend libpil-python-backend

stand-alone compiler $ pilc -i application.pil --java $ pilc -i application.pil --python

✔ abstract from platform ✔ familiar concrete syntax ✔ cheap to port easy DSL compiler integration platform interaction

✔ abstract from platform ✔ familiar concrete syntax ✔ cheap to port ✔ easy DSL compiler integration platform interaction

platform interaction

external class pil::web::Request { String getParameter(String name); ... } platform-speciﬁc implementations

Java implementation package pil.web; import javax.servlet.http.*; public class Request { private HttpServletResponse r; public Response(HttpServletResponse r) { this.r = r; } public String getParameter(String name) { return r.getParameter(name); } ... }

Python implementation import cgi class Request(object): def __init__(self): self.fs = cgi.FieldStorage() def getParameter(self, name): return self.fs[name] ...

NHibernate

external class db::DatabaseSession { void beginTransaction(); void rollback(); void commit(); List<Object> getAll(Class cls); void persist(Object o); void delete(Object o); }

WebDSL ORM PIL Interface Hibernate Java Python SQLAlchemy

query API/language?

query API/language? persistence behavior?

WebDSL PIL/ORM PIL Java Python

✔ abstract from platform ✔ familiar concrete syntax ✔ cheap to port ✔ easy DSL compiler integration ✔ code-generation speciﬁc abstractions platform interaction

✔ abstract from platform ✔ familiar concrete syntax ✔ cheap to port ✔ easy DSL compiler integration ✔ code-generation speciﬁc abstractions ✔ platform interaction

conclusion

retargetability problem: software platforms

retargetability problem: software platforms maintaining platform back-ends is expensive

retargetability problem: software platforms maintaining platform back-ends is expensive PIL

retargetability problem: software platforms maintaining platform back-ends is expensive PIL PIL/G

Java & Python back-ends

Java & Python back-ends Stratego/XT

pil-lang.org webdsl.org twitter.com/zef

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PIL - A Platform Independent Language

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