Areas of work


Study groups



Program transformation

We explore the use of program transformation techniques for manipulating CAL actor specifications, and compositions of CAL actors. Transformations on single actors can be used to optimize a CAL specification, or to bring it into a canonical form expected by some code generator or some other language processor (cf. code generation). The transformations are expressed as XSLT scripts manipulating the XML document that represents the CAL abstract syntax tree. (More info on CAL and XML and XSLT can be found here.)

Transformations in code generation

As outlined in the section on code generation, program transformations are used to bring a CAL actor specification into a form that is easier for a particular code generator to produce code for. These transformations express some language constructs by other, more canonical, constructs, or they annotate the program with information such as types, variable dependencies etc. They may also depend on each other. A map of existing program transformations can be found here.

Models of computation

Another use of program transformations is in the definition of what it means to compose a network of actors. The description of such an actor compositor function as a program transformation may be considered as an approach to a notion of 'model of computation'..

Figure 1: Alternative ways to realize actor composition.

The idea is that rather than using code generators or interpreters in order to realize a model of computation, we consider a model of computation to be an actor composition function, i.e. a mechanism that takes a network of actors and creates a single new actor from it. The resulting actor may of course be further composed, or it may be fed to the CAL code generation infrastructure.

A good introduction to these ideas can be found in these slides by Chris Chang.

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