The transformer

HLSIM uses program transformation to convert the user's Scheme program into a form that can be executed efficiently in the simulation environment. The cps procedure (command) performs the transformation on a Scheme source file.

Questions:

``Why bother transforming the Scheme program?''

``Can't you just run Scheme directly?''

``Why don't you just write the communications primitives to context switch''

``Why not wrap the whole program in a lambda and cps-cpnvert that'' [top level environment too rigid, opaque, and cant run code in that context].

The transformation approach addresses all of the following requirements for the simulator.

• Programs should be expressed in a high level language, e.g. Scheme, and not be overly burdened with artifacts of the simulation mechanism (e.g. calls to yield, explicit construction of saved state).
• The ability to model time accurately.
• Modelling of asynchronous events (interrupts).
• Many (thousands) of programs running together. It is important that we can do simulations on ensembles large enough that bulk behaviour to appears.
• Execution efficiency. It is desirable for the simulation to run as fast as possible without sacrificing accuracy.

Conceptually, the gunk program is a program running on many machines. The simulator is a program running on one machine.

The transformer compiler enforced cooperative multitasking

Alternatives:

call-with-current-continuation

Interpreter -- slower.

 
• Continuation passing style
• The engine transformation
• Explicit store