Getting Started in PL Design Research

1
Getting Started in PL Design Research

• Stephanie Weirich
• University of Pennsylvania

2
About Stephanie Weirich

• Texan by birth
• grew up in Dallas, attended Rice University
• Pennsylvanian by marriage
• Met Steve Zdancewic at grad school (Cornell)
• Both PL faculty members at Penn since 2002
• Mother of 1.5 girls
• Eleanor Jane Weirich Zdancewic,
• Jan 2005
• ?????, Aug 2007
• Research interests
• type systems
• functional programming

3
My research

• How can we make statically-typed programming
  languages more expressive?
• Type-directed Programming Programs that depend
  on types
• Reflect type information structure into data
• Express generic algorithms that work for many
  different data structures
• AspectML, RepLib in Haskell, Type-directed Java
• Dependent Types Types that depend on programs
• Use types to statically verify program invariants
• Programmable type systems (conditional
  relationships)
• New language/type system design PIE
• Type inference
• Making it easier to use advanced type systems
• Extensions to the Haskell programming language

4
Where to begin?

• Start by building background and experience
• Read, Read, Read
• Learn by doing write programs, do proofs
• Study textbooks e.g. Pierce, TAPL
• Learn how to evaluate design work
• Identify important problems
• Work on something that seems cool, even if you
  dont know what the contribution will be
• Staring at a blank piece of paper will not
  produce a POPL submission.

5
Where to look for publications

• Conferences Workshops
• POPL ICFP
• PLDI, OOPSLA, ESOP, LICS, PPDP
• Journals
• JFP and TOPLAS
• Seminars, web pages
• Once youve identified the active participants
  for your problem

6
Play with languages

• Play around with many different languages
• Mature FPLs
• Haskell (GHC)
• ML (O'Caml, Standard ML)
• Scheme (PLT Scheme)
• Research FPLs
• Scala, Omega, ATS, GHC extensions
• Why?
• Learn by doing
• Might find new uses for old types
• Might discover connections between features

7
Learn about constructive logic

• Logical foundation for formal models of languages
• Books/Lecture notes
• Barendregt Lambda Calculi with Types
• Pfenning Computation and Deduction
• Sorenson, Urzyczyn Lectures on the Curry/Howard
  Isomorphism
• Proof assistants for constructive logic
• Twelf
• Coq
• Coq Tutorial at POPL 08 (tentative)

8
Expressiveness

• Build a small interpreter/write small programs
• Build a larger implementation/write larger
  programs
• Port existing programs to new language
• Example Cyclone
• Extend existing language with active user
  community
• Example GHC

9
Consistency

• Does the design make sense?
• Can it be implemented?
• Can we prove properties about a formal model of
  it?
• Type soundness
• Decidable type checking
• Algorithmic complexity

10
Aesthetics

• Does the design follow general design principles?
• Simplicity
• Orthogonality
• Mathematical insight
• Does the design include a foundational building
  block for future languages? Add to our
  mathematical vocabulary?

11
Relevance/Significance

• Is there a need for this design?
• Example Concurrency, motivated by new hardware
• Does this design teach us about programming and
  program structure?
• Example Monads

12
What to work on?

• What are people talking about now?
• What will they be talking about in the next few
  years?
• What are the important questions?
• Another perspective
• Pierce, LICS 2003 invited talk. Types and
  Programming Languages The Next Generation

13
Expressive type systems

• How do we show that there are no bugs in linux
  device drivers/garbage collectors/embedded
  systems/etc?
• Types for modeling memory management, state
  invariants, and running time, eliminating race
  conditions, deadlock

14
Dependent type systems

• How can we stop designing all these special
  purpose type systems? Can we make the type system
  programmable? How can the user cope with such
  complicated types?
• Indexed types, GADTs, full-spectrum dependency,
  PADS, etc.

15
Program equivalence

• How do we show that two programs are the same?
• How can we show that program abstractions are
  preserved? Even in a multi-lingual system?
• Can the design of the language help?
• Bisimulation techniques, type abstraction,
  logical relations, encryption, security-type
  systems

16
Concurrency

• What is the right programming model for
  concurrent architectures?
• Software Transactions?
• Deterministic concurrency?
• Message-passing?
• How do we reason about concurrent programs?
• Does purity help?

17
How to evaluate language designs?

• Need to know to do good work
• Need to know to present that work effectively
• Difficult (and sometimes controversial) question
• Different axes
• Novelty
• Expressiveness
• Consistency
• Aesthetics
• Relevance