Replace LETREC with "relaxed" internal definitions.

[ramsdell%linus@mitre-bedford.ARPA]

I just received a copy of the Proposals for a R4SR.  To my surprise, I
found my wish that a dependency analysis be done on local definitions
was taken as proposal to be discussed at Sunday's meeting.  I intended
the subject come up only in informal discussions.  In order to
realistically institute such a big change, I would have to show an
efficient implementation in both an interpreter and a compiler, and
convince a number of people it is a good idea, before the subject is
discussed at a meeting.  That time is curtainly not now.

I submitted the recent notes on this subject in response to Eric
Tiedemann's message on the specification of the order in which
elements of a combination are evaluated.  In his note, he talked about
finding an "applicative order fixpoint" of LETREC, to solve Robert
Hieb's complaint that internal definitions look like top-level
definitions, but do not act like them.  Someone then complained that
finding an applicative order fixpoint is uncomputable.  However, a
dependency analysis is all that is needed, and I gave an algorithm
that does the analysis.

Please withdraw the proposal to Replace LETREC with "relaxed" internal
definitions.  My proposal to eliminate NIL and T from the report is
quite serious.

John