Extensions to the Ego Language

1
Extensions to the Ego Language

• Matthew Kehrt
• Advisor Jonathan Aldrich

2
Objects

• Provide a convenient representation of some piece
  of modeled system
• Contain ways of working with current state
• Use can change over time
• Opening a socket
• Regular expression matching

3
Dynamic Inheritance

• Introduced in the Self language
• Can model changes in object usage
• Causes runtime changes in an objects interface
• Changing interface can allow calls to methods
  that dont exist

4
Static Analysis

• Static typechecking can prevent runtime errors
• Ego introduced a type system for a Self like
  language
• Prevented calling nonexistent methods on objects
• Linear type system allows inheritance to change
  only for objects with one reference

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Weaknesses of Ego

• Ego is theoretically useful but missing useful
  features
• Linearity constraints can make programming
  difficult
• Type annotations currently needed are often large
• The Ego syntax is nonstandard and unwieldy

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Extensions to Ego

• I propose to extend Ego to eliminate these issues
• Type inference can eliminate type annotations
• There are known linguistic constructs for easing
  the linearity constraint
• More standard syntax can be introduced

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Importance

• Ego and Self introduced useful language features
  and a type system for preventing errors in their
  use.
• I hope to demonstrate the ability to add features
  to this system to increase its usability.

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Progress

• Syntax has been substantially reworked
• Currently working on methods for easing linearity
  constraint
• Future work will include
• type inference or other methods for reducing type
  annotations
• proof of type safety and linearity constraint

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Evaluation

• Success evaluated based on achievement of goals
• Is our system clean and foundational?
• Were we able to produce an effective method of
  type inference?
• Can we ease the linearity constraint while still
  preventing runtime errors?
• Our system must be typesafe and enforce
  linearity.

10
References

• M. Abadi, L.Cardelli. A theory of objects.
  Springer, 1996.
• Andi Bejleri, Jonathan Aldrich, and Kevin
  Bierhoff. Ego Controlling the Power of
  Simplicity. Submitted for publication.
• K. Fisher and J. C. Mitchell. A Delegation-based
  Object Calculus with Subtyping. In Proc.
  Fundamentals of Computation Theory, 1995.
• D. Ungar, R. B. Smith. Self The power of
  simplicity. Proc. Object-Oriented Programming
  Systems, Languages and Applications
• P. Wadler. Linear types can change the world!
  In M. Broy and C. Jones, editors, Programming
  Concepts and Methods, North Holland, 1990