THE SCOTTISH PROGRAMMING LANGUAGES SEMINAR

		       Thursday 6 December 2012
		      University of Strathclyde
	     Livingstone Tower, room LT1415, 12.00-17.30



Programme

--12.00-13.30----Lunch (sandwiches, etc, will be provided)-----------

  13.30-14.00  Neel Krishnaswami                  (Birmingham)
               Simple and Efficient Higher-Order Reactive Programming

  14.00-14.30  Chris Brown                        (St Andrews)
               The ParaPhrase Project:
               Parallel Patterns for Heterogenous Multicore Systems

--14.30-15.00----Coffee----------------------------------------------

  15.00-15.30  Sam Lindley                        (Strathclyde)
               Handlers in Action

  15.30-16.00  Danel Ahman                        (Edinburgh)
               Computational effects (and their handlers)
               in normalization by evaluation

--16.00-16.30----Coffee----------------------------------------------

  16.30-17.00  Jeremy Singer                      (Glasgow)
               JVM Linguistics:
               A dynamic analysis of Non-Java JVM languages

  17.00-17.30  Simon Fowler / Philip Hölzenspies  (St Andrews)
               Tactile Terms demonstration

--17.30-18.30----Pub-------------------------------------------------

Actions for You

  * Please let me know if you're coming for lunch, so we can guess how
      many little things on sticks, etc there should be. Do indicate if you
      would like some influence over what sort of things are on the sticks.

  * Please let me know if you're interested in staying for dinner. I'd be
      happy to book somewhere, but they always want numbers. I'm currently
      inclined towards Italian food, but I could be persuaded otherwise.




Abstracts


  13.30-14.00  Neel Krishnaswami                  (Birmingham)
               Simple and Efficient Higher-Order Reactive Programming

Functional reactive programming (FRP) is an elegant approach to
declaratively specify reactive systems. However, the powerful
abstractions of FRP have historically made it difficult to predict and
control the resource usage of programs written in this style.

In this talk we give a simple type theory for higher-order func-
tional reactive programming, as well as a natural implementation
strategy for it. Our type theory simplifies and generalizes prior type
systems for reactive programming. At the same time, we give a an
efficient implementation strategy which eagerly deallocates old
values, ruling out space and time leaks, two notorious sources of
inefficiency in reactive programs. Our language neither restricts the
expressive power of the FRP model, nor does it require a complex
substructural type system to track the resource usage of programs.

We also show that for programs well-typed under our type system, our
implementation strategy of eager deallocation is safe: we show the
soundness of our type system under our implementation strategy, using
a novel step-indexed Kripke logical relation.


  14.00-14.30  Chris Brown                        (St Andrews)
               The ParaPhrase Project:
               Parallel Patterns for Heterogenous Multicore Systems

Enabling programmers to "think parallel" is critical if we are to be
able to effectively exploit future multicore/manycore architectures.
In this talk I will introduce paraphrasing: a new approach for
constructing parallel programs using formally-defined refactoring
transformations.  I will introduce a number of new refactorings for
Erlang that capture common parallel abstractions, such as maps, farms
and pipelines, and show how these can be used by a refactoring tool,
to introduce and tune parallelism, using cost-models as guidance.

Using a paraphrasing approach, we are able to easily obtain
significant and scalable speedups in Erlang (up to 4.9 on an 8-core
machine).


  15.00-15.30  Sam Lindley                        (Strathclyde)
               Handlers in Action

Plotkin and Pretnar's handlers for algebraic effects occupy a sweet
spot in the design space of abstractions for effectful computation. By
separating effect signatures from their implementation, algebraic
effects provide a new level of modularity allowing programmers to
express effectful programs independently of the concrete
interpretation of their effects. A handler is an interpretation of the
effects of an algebraic computation.

The handler abstraction adapts well to multiple settings: pure or
impure, strict or lazy, static or dynamic typing. I will give a gentle
introduction to its use and a collection of illustrative
examples. Time permitting, I will describe our implementation in
Haskell, outline other implementation strategies, and present
preliminary results on the impact of the high level of abstraction on
performance.


  15.30-16.00  Danel Ahman                        (Edinburgh)
               Computational effects (and their handlers)
               in normalization by evaluation

I shall summarize the work undertaken during my MPhil project on
formalizing normalization by evaluation (NBE) for Levy's fine-grained
call-by-value (FGCBV) language extended with Plotkin-Power algebraic
value and effect theories. I will show how free monads, Kripke logical
relations and semantics based on partial equivalence relations make
both the definition of the normalizer and the correctness proofs neat
and straightforward.

If time permits, I will also outline the latest work on extending
Levy's FGCBV language and the NBE algorithm with Pretnar's handlers of
computational effects. This will include discussing two possibilities
of handling computations (into computations or into values) and
various subtleties both in giving the handlers an equational theory in
FGCBV and defining normal handlers that are identity on operations.


  16.30-17.00  Jeremy Singer                      (Glasgow)
               JVM Linguistics:
               A dynamic analysis of Non-Java JVM languages

The rapid adoption of non-Java JVM languages is impressive: major
international corporations are staking critical parts of their
software infrastructure on components built from JVM languages such as
Scala and Clojure. However, to date there has been no principled
comparison of how these languages interact with the JVM. I will
describe an exploratory data analysis of the dynamic behaviour of five
widely used JVM languages. We discover divergence in dynamic behaviour
from Java programs, and discuss the implications of these differences
for the performance of JIT compilation and garbage collection.


  17.00-17.30  Simon Fowler / Philip Hölzenspies  (St Andrews)
               Tactile Terms demonstration

Programming languages with strong type systems have proven their use
in disallowing erroneous programs. Arguably, therefore, as many
programs as possible should be written in a strongly typed
language. Uptake of such languages by the programming community at
large, unfortunately, is slow. Worse still, strongly type languages
are losing ground to dynamically typed languages, like Python, Ruby,
Perl and PHP. We believe the rejection of strong types by many people
stems from the experience that they make for complicated
languages. Type errors seem to have an especially deterring effect on
students and programming novices. The alternative programmer-compiler
interaction presented in this demonstration is aimed at making strong
types more accessible to the mainstream of programming, as well as
providing expert programmers in these languages with a comfortable and
fast development tool. This is achieved, not by using graphical
metaphors for terms, but by giving users per-modification feedback on
the types of their terms - including the rejection of the construction
of ill-typed terms - and a more visual presentation of these (still
textual) terms than simple (syntax highlighted) text.