Controlling parallelism and data distribution in Eden

The parallel functional language Eden uses explicit processes to export computations to other processor elements and to achieve parallelism. As Eden is based on the non-strict functional language Haskell, this raises the question in which way and to which degree the lazy evaluation strategy of Haskell should be transferred to the parallel setting. A modification is needed, as a completely demand driven evaluation would not lead to real parallelism but only to distributed sequentiality. The non-existence of a global shared memory for all processes raises a second question, namely, how shared data should and can be distributed across the available processing elements. In general, one has to choose between data duplication via communication and work duplication by recomputation. In total we will discuss the interaction of laziness, parallelism and data distribution in Eden. We explain the evaluation model underlying Eden’s parallel implementation and justify corresponding design decisions.