David J. Pearce (Blog)

Actors on the JVM

Tuesday, March 22nd, 2011

The Actor Model is an interesting alternative to the standard threading model used in languages like Java. Its been around for a while, but Erlang has recently brought it into the mainstream.

Implementing Structural Types

Monday, March 7th, 2011

Introduction Over the last few months, I’ve been working on the type system underpinning Whiley. A key feature is the use of structural typing, rather than nominal typing, and I’ve blogged about this quite a bit already (see [1][2][3][4]).

Freakonomics

Wednesday, February 23rd, 2011

Recently, I finished reading Freakonomics, by Steven Levitt and Stephen Dubner. and I have to say that I really liked it!! The book is focuses on the study of everyday aspects of life using the tools of economics and statistics.

Minimising Recursive Data Types

Wednesday, February 16th, 2011

Following on from my previous post about structural subtyping with recursive types, a related problem is that of minimising recursive types. Consider this (somewhat artificial) example: define InnerList as null | { int data, OuterList next } define OuterList as null | { int data, InnerList next } int sum(OuterList list): if list ~= null: return 0 else: return 1 + sum(list.

A Problem with Structural Subtyping and Recusive Types

Tuesday, February 15th, 2011

One problem causing me a headache is how to implement structural subtyping for recursive types (which I first blogged about here). The following example illustrates the basic idea: define Link as { int data, LinkedList next } define LinkedList as null | Link LinkedList f(Link list): return list This is a fairly straightforward definition of a linked list, along with a dumb function f() that just returns its parameter.

What Motivates Us?

Monday, February 7th, 2011

Here’s an interesting video that I just came across (adapted from Dan Pink’s talk at the RSA, which is currently doing the rounds: The video is about what motivates people to do things and, in particular, whether or not giving people more money means they do a better job.

The Case Against Structural Subtyping ... ?

Wednesday, January 26th, 2011

My previous post on structural subtyping generated quite a few comments over on reddit. There were a lot of mixed opinions as to the pros and cons of having a structural type system instead of a nominal type system.

One Approach to Efficient Structural Subtyping

Friday, January 14th, 2011

An interesting challenge with structural subtyping is that of efficient implementation. In particular, without care, it may be impossible to determine a static offset for each field in a structure at runtime, meaning every field access will require a dictionary lookup.

Modular Purity Analysis for Java

Tuesday, December 14th, 2010

Well, after an agonizing wait I finally heard the news that my paper on purity analysis was accepted to the Conference on Compiler Construction, 2011. Obviously, I’m stoked! The paper is:

Why not use Structural Subtyping?

Monday, December 13th, 2010

Modern programming languages generally use what is known as a Nominal type system. This means types are associated with explicit names and subtyping relationships are explicit in the code (e.g. via extends or implements).