Recursive Abstract State Machines

The abstract state machine (ASM) thesis, supported by numerous applications, asserts that ASMs express algorithms on their natural abstraction levels directly and essentially coding-free. The only objection raised to date has been that ASMs are iterative in their nature, whereas many algorithms are naturally recursive. There seems to be an inherent contradiction between

• the ASM idea of explicit and comprehensive states, and
• higher level recursion with its hiding of the stack.

But consider recursion more closely. When an algorithm A calls an algorithm B, a clone of B is created and this clone becomes a slave of A. This raises the idea of treating recursion as an implicitly multi-agent computation. Slave agents come and go, and the master/slave hierarchy serves as the stack.

Building upon this idea, we suggest a definition of recursive ASMs. The implicit use of distributed computing has an important side benefit: it leads naturally to concurrent recursion. In addition, we reduce recursive ASMs to distributed ASMs. If desired, one can view recursive notation as mere abbreviation.