modules

[linus!ramsdell@Mitre-Bedford.ARPA]

A while ago, I sent a message to t-discussion suggesting that
modules of the style used in KL0 Prolog, be included in T.
Since then I tried to implement the suggestion as a macro,
but since HERALD cannot be created via a macro, the implementation
was useless.

While thinking about all of this, I came upon the following puzzle.
Consider a program organized as they are in PASCAL. In T one would
write a sequence of LET*'s and LABELS as an equivalent structure.
LABELS are needed for forward declarations and recursive type declarations.
To make a program that allows dynamic linking of this nested program
structure, it makes sense to use hierarchially arranged LOCALES.

Newer compiling languages use the idea of modules each with
a list of items exported from the module, and a list of modules
used by this module. A program is a collection of module declarations,
a module use list, an expression to be evaluated in the environment
of the modules.

(MODULES
  (mod-decl mod-decl ...)
  (used modules)
  implicit block)

mod-decl ::= (name (used-modules) ??some expression that returns 
					the items exported??).

The puzzle is to write MODULES without using LOCALES, e.g.
use LAMBDA, LABELS, IF, QUOTE, ..., but not DEFINE, LOCALE,
*VALUE, or others.

If this is impossible, maybe facilities giving dynamic linking
module structure should have a parallel static structure just
as LOCALES have LABELS.
John