constant folding/smashing

[Jon L White <edsel!jonl@labrea.stanford.edu>]

re:     What about constant hash-tables?  No variety of QUOTE can build
        a constant hash table because there is no notation for them.
        (I don't count #.(make-hash-table...) because it's so gross.)

Lucid's "Re-Targetable" compiler is table driven; the tables are ordinary
CL hashtables.  In recent images, they are stored in read-only memory, since
all the key entries are symbols, and since they change very rarely (such
as when someone is debugging the compiler).  A "lazy migration" scheme
ensures that they become writeable upon demand.

There is a proposal before X3J13 now (presented by Dave Touretzky) to
give a printable representation to hashtables.  If a sufficiently powerful 
version of it is adopted, then it should be possible to use QUOTE to 
reference a constant hashtable.

I don't think the techniques that Lucid uses to build read-only tables
are exported to the end-user; but it certainly is possible to reference
"constant" hashtables using the "gross" #. notation, and have such code 
be compiled and loaded correctly.


-- JonL --