Refill a generative java dialect

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Refill a generative java dialect

• Kasper Østerbye
• IT University Copenhagen

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Goals of refill project

• Goal of this project is to provide a framework
  for language extension
• Add new language constructs
• add new sub/embedded languages
• extend/change existing name binding rules
• extend static type checking mechanism
• extend compile time semantics
• change the code generation
• transform the new constructs into base language
• multi-target compilation
• Focus on two aspects of this
• Achieving the functionality to do the above
• Specification style matters

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An extensible Java

• There are two parties to a language extension,
  the language extender, and the language user.
• The language user is assumed to have knowledge of
  the base programming language, and knowledge on
  the domain of the language extension.
• The language extender is assumed to be an expert
  in the base language, and expert in the domain of
  the language extension.
• but not necessarily an expert in compiler
  construction

import mycontrolstructures.ForEach import
java.util.Vector class Test Vector employees
new Vector()   public void printAllEmplees()
foreach Person p in employees
System.out.println(p.name
p.address)
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Defining foreach, syntax and name binding

• package controlstructures
• import refill.java.Statement
• import refill.java. NameAppl
• import refill.java. NameDecl
• class ForEach extends Statement
• // foreach Person p in collection do statement
• syntax "foreach" NameAppl type NameDecl element
  "in" NameAppl col "do" Statement stmt

Environment binding(Environment e) // create
a new environment based in e. Environment newE
e.extendEmpty() type.findFrom(e) newE.bind
(element, type) stmt.binding(newE) col.bindF
rom(e) return e
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Static semantics

• void check()
• if (! col.isBound() )
• check.error(col, col.name
• " is not defined, or is misspelled")
• if ( !type.isKindOf(Collection) )
• check.error(col, col.name
• " should be a Collection")
• stmt.check()
•  

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Transformation

• void transform()
• // Person p Iterator i col.iterator()
• // while (i.hasNext() )
• // p (Person)i.next()
• // stmt
• //
• String iteratorID newIdentifier()
• Statement substitution new Block(
• " " type " " element " Iterator "
• iteratorID " " col ".iterator()\n"
• "while (" iteratorID ".hasNext() )\n"
• element " (" type ")" iteratorID
  ".next()\n"
• stmt ""
• this.replace(substitution)

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Issues further directions

• How to extend with sub-languages rather than
  single constructs
• How to make sure that sub-languages do not
  interfere
• Better ways to specify transformations
• Get it all implemented
• Find the formal limitations of how to add new
  constructs to the language with the present
  algorithm.