Formal comment #110 (simplification)

Remove double phase semantics
Reported by:	Andre van Tonder

Component:	presentation
Version:	5.91

Pages : 24 

Summary

Libraries can be greatly simplified by removing current double choice
of phase semantics.

Description

The current phase semantics is very complicated and the choice of two
separate semantics hinders portability.

A simpler semantics is already effectively implemented by two of the
reference implementations. This semantics shares one set of bindings
between all the levels into which they are imported.

The visit/invoke semantics becomes HUGELY simplified in this case.

Note that the following is equivalent to the current draft when the
bindings are shared. It is what the "dybvig-ghuloum" and "vanTonder"
implementations already effectively do.

To visit a library: 

Visit any library that is imported by this library and that has not
yet been visited.

For each k >= 1, invoke any library that is imported by this library
for .... (meta k), and that has not yet been invoked.

Evaluate all syntax definitions in the library.

To invoke a library: 

Invoke any library that is imported by this library and that has not
yet been invoked.

Evaluate all variable definitions and expressions in the library.

RESPONSE:

R6RS will maintain a compromise position that allows both shared and
unshared instances.

See the response to formal comment #92 for further explanation.