This paper describes Cola, an object-oriented command language for Hydra; Hydra is a capability-based operating system that runs on C.mmp, a tightly coupled multiprocessor. The two primary aspects of Cola, that it is a command language for Hydra, and that it is based on the object paradigm, are examined. Cola was designed to effect a correspondence between capabilities in Hydra and objects that are supported by the language. Cola is based on Smalltalk in that it uses message-passing as a control structure to allow syntactic freedom in the expression of commands to the system. Cola objects are arranged in a hierarchy, and the message-passing mechanism was designed to exploit this structure by automatically forwarding an unanswered message up the hierarchy. Two ramifications of this mechanism, automatic inheritance and shadowing, are discussed. An evaluation of the design decisions is also given.
- command language
- knowledge representation languages
- object hierarchies
- object-based languages
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