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PE report (section 5)

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Relation to existing environments (Lisp, Mesa, Smalltalk)

The relationship between our desired EPE capabilities and our existing language systems is complicated by the fact that there are two Lisp systems and two Smalltalk systems that must be taken into account. The present Lisp and Smalltalk systems have a kernel written in Bcpl and Alto assembly language respectively; they do most of their I/O directly. This implementation limits them to using 128K of memory and makes communication with the Mesa world on the Dorado very difficult.

It is intended that the Lisp kernel be converted from Bcpl to Mesa, and that Lisp’s current I/O and paging facilities be replaced by those in Pilot. There is no current time schedule or manpower commitment for this effort. However, we believe that this step is unavoidable if Lisp is to serve as the base for an EPE. Accordingly, our difficulty estimates reflect the assumption that this has been done. The conversion process itself is somewhere between 1 and 2 in our coding scheme.

Smalltalk is in somewhat worse shape, since the current implementation uses an object swapping scheme and an addressing mechanism that do not scale up well. There is a design, roughly 85% complete, for a high-performance Smalltalk for the Dorado that uses paging and differs in many ways from the current Alto implementation: this design has been scrutinized by many people, but is not ready to implement. We believe that such a re-implementation is mandatory if Smalltalk is to serve as the base for an EPE: it has difficulty somewhere between 2 and 3. Again, our difficulty estimates assume that this basic step has been taken.

Mesa already has nearly all the machinery required to take advantage of the Dorado environment. The chief question mark at the moment is the availability of Pilot for the Dorado, which again we assume as a prerequisite. We are not aware that any manpower has been committed to this end. Bravo, the only editor currently used for Mesa programs, does not run well on Dorado and cannot be integrated into the Mesa/Pilot environment; we assume that some Mesa-implemented editor, perhaps Diamond or part of Laurel, will be available.