Talk at University of Hull Computer Science Seminar

‘Tis the season

… to give an end-of-year update of what is happening with the PM language. It is a long time now since I wrote a PM blog. However, behind the scenes there has been a lot of work done on the guts of the compiler with new inference and optimisation passes added and others taken apart, polished, and put back together again. New language features have also been implemented, including methods, improved object lifetime management and, most importantly, a radically simplified approach to coding stencils. The handling of stencils was one aspect of PM-0.4 with which I was least happy. Since these are a key requirement for nearly all numerical modelling, I have long been looking for a way to make their coding as straightforward as possible. However, this has been one of the greatest challenges in terms of implementation, since the amount of code restructuring need to make a stencil operate efficiently (separating out halo computation, overlapping computation and halo exchange, tiling and the in...

Compile time, run time, coffee time

[ Please note that in the following discussion I will be using PM 0.5 notation, which is slightly different to PM 0.4 and also in some flux as PM 0.5 is still in development. ] Many programming languages (and most newly developed ones) include some form of compile-time programming, ranging from simple preprocessors ( #define , #if in C) to fully blown macro systems capable of re-writing the abstract syntax tree during compilation (Rust, Julia, etc .). In line with its philosophy of keeping things as simple as possible, but not simpler, PM takes a middle road with compile-time programming supported primarily through the type system. There is nothing too radical here – this is not an area where the language aims to break new ground. The PM approach centres around the use of compile-time types. Many languages use special types to denote literal values and PM follows this trend. Literal integers, reals, strings and Booleans each have their own types: literal(int) , litera...

Communicating Operators - The Heart of PM

Communicating operators lie at the heart of the PM parallelisation model. They are designed to provide a compromise between the direct access to global data structures (particularly arrays) offered by approaches such as Partitioned Global Address Space and the straightforward synchronisation provided by Communicating Sequential Processes . I n common with most data-parallel languages, PM contains a parallel version of the for statement which runs all invocations of its enclosed statement list concurrently: for element1 in array1, element2 in array2 do element2=process_element(element1) endfor Most real models will require some interaction between adjacent array elements. In PM this is achieved by using either a local or a global communicating operator. The global operator @v returns an array whose elements comprise the values of loop-local variable v in each invocation of the enclosing for statement. The neighbourhood operator v@{nbd ...

PM Programming Language

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