Getting Started in PL
Design Research
Stephanie Weirich
University of Pennsylvania
About Stephanie Weirich
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Texan by birth
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Pennsylvanian by marriage
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Met Steve Zdancewic at grad school (Cornell)
Both PL faculty members at Penn since 2002
Mother of 1.5 girls
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grew up in Dallas, attended Rice University
Eleanor Jane Weirich Zdancewic,
Jan 2005
?????, Aug 2007
Research interests
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type systems
functional programming
My research
How can we make statically-typed
programming languages more expressive?
Type-directed
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Reflect type information structure into data
Express generic algorithms that work for many different data
structures
AspectML, RepLib in Haskell, Type-directed Java
Dependent
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Type
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Programming: Programs that depend on types
Types: Types that depend on programs
Use types to statically verify program invariants
“Programmable” type systems (conditional relationships)
New language/type system design: PIE
inference
Making it easier to use advanced type systems
Extensions to the Haskell programming language
Where to begin?
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Start by building background and experience
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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 don’t know what the contribution will be
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Staring at a blank piece of paper will not produce
a POPL submission.
Where to look for publications
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Conferences & Workshops
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Journals
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POPL & ICFP
PLDI, OOPSLA, ESOP, LICS, PPDP
JFP and TOPLAS
Seminars, web pages
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Once you’ve identified the active participants for
your problem
Play with languages
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Play around with many different languages
Mature FPLs:
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Research FPLs:
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Haskell (GHC)
ML (O'Caml, Standard ML)
Scheme (PLT Scheme)
Scala, Omega, ATS, GHC extensions
Why?
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Learn by doing
Might find new uses for old types
Might discover connections between features
Learn about constructive logic
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Logical foundation for formal models of languages
Books/Lecture notes:
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Proof assistants for constructive logic
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Barendregt: Lambda Calculi with Types
Pfenning: Computation and Deduction
Sorenson, Urzyczyn: Lectures on the Curry/Howard
Isomorphism
Twelf
Coq
Coq Tutorial at POPL 08 (tentative)
Expressiveness
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Build a small interpreter/write small programs
Build a larger implementation/write larger
programs
Port existing programs to new language
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Example: Cyclone
Extend existing language with active user
community
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Example: GHC
Consistency
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Does the design make sense?
Can it be implemented?
Can we prove properties about a formal
model of it?
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Type soundness
Decidable type checking
Algorithmic complexity
Aesthetics
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Does the design follow general design
principles?
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Simplicity
Orthogonality
Mathematical insight
Does the design include a foundational
building block for future languages? Add to
our mathematical vocabulary?
Relevance/Significance
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Is there a need for this design?
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Example: Concurrency, motivated by new
hardware
Does this design teach us about
programming and program structure?
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Example: Monads
What to work on?
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What are people talking about now?
What will they be talking about in the next few
years?
What are the important questions?
Another perspective:
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Pierce, LICS 2003 invited talk. Types and
Programming Languages: The Next
Generation
Expressive type systems
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How do we show that there are no bugs in
linux device drivers/garbage
collectors/embedded systems/etc?
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Types for modeling memory management,
state invariants, and running time, eliminating
race conditions, deadlock
Dependent type systems
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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?
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Indexed types, GADTs, full-spectrum
dependency, PADS, etc.
Program equivalence
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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
Concurrency
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What is the right programming model for
concurrent architectures?
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Software Transactions?
Deterministic concurrency?
Message-passing?
How do we reason about concurrent
programs?
Does purity help?
How to evaluate language
designs?
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Need to know to do good work
Need to know to present that work effectively
Difficult (and sometimes controversial) question
Different axes:
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Novelty
Expressiveness
Consistency
Aesthetics
Relevance