Added :around option to defrule

[scymtym]

This patch makes defrule accept an additional :around option with syntax

(:AROUND ([&BOUNDS START [END]]) BODY)

BODY has to call CALL-TRANSFORM to invoke the primary transform of the rule.

This feature can be used to implement things like a stack of nested symbol tables (see new file example-symbol-table.lisp).

Remaining problems:

• documentation string is clunky
• not sure whether the patch interacts properly with the cache mechanism
• code duplication in compile-rule

[scymtym]

Not to be pushy, but may I ask whether you are basically willing to merge this at some point?

[nikodemus]

Merged.

[scymtym]

Thanks!