Re: reexport-from-module

[thi <ttn@mingle.glug.org>]

Jost Boekemeier writes:

 > Could you please explain the semantics of re-exporting and renaming
 > of symbols?

Sure.  Exporting a symbol makes its variable binding available in a
module's public interface, where another module can do `use-modules' or
`:use-module' to get to them.  For example, the sequence:

	(define-module (A))
	(define-public pi 3.1415)
	(define-module (C) :use-module (A))
	(define-module (D) :use-module (C))

makes `pi' available for use by module C, but not module D.  In order
for D to see `pi', C would need to re-export `pi', ie, add `pi' to its
public interface.  (Currently, you can do this using `export', or
`define-public'.)

Renaming is simply defining a new symbol to bind to the variable of
another one.  (Currently, you can do this using `define'.)

Suppose D wants `pi' defined as 3.14, but still wants access to A's
`pi', which it considers `exact-pi'.  Then, the sequence:

	(define-module (A))
	(define-public pi 3.1415)
	(define-module (C) :use-module (A))
	(define-public exact-pi pi)
	(define-module (D) :use-module (C))
	(define pi 3.14)

would be a case of both re-export as well as renaming, and D would be
able to use `pi' as well as `exact-pi'.  Hmmm, one doesn't need weird
syntactic cruft like `reexport-from-module' at all.  (I rescind my
desire to see it added to guile, having learned something by doing this
explanation -- thanks!)

Feeling goofy, :-D
thi