On Sep 6, 2009, at 10:51 AM, Brian Mastenbrook wrote:
> * To aid in meta-programming at the REPL, the top-level environment
> previously created at the REPL can be assigned a name and be made
> available as a library for import at this point. In an implicitly-
> phased implementation, the bindings are available directly. A
> separate-
> instantiation implementation must record the top-level forms entered
> at the REPL for future instantiations of the library.
In the example, I showed how a separate-instantiation implementation
would re-instantiate the previous top-level-program-as-library when
entering a new top-level program which imports the previous top-level
program. After thinking about this for a minute, I believe it would be
desirable for even a separate-instantiation implementation to avoid
this behavior *if* only one instantiation is required. For example:
> #!r6rs
(import (rnrs base (6))
(rnrs io simple (6))) ; I also missed this in my previous
example
> (define a (begin (display "hi") (lambda (stx) 42)))
OUTPUT: hi
> #!r6rs
(import (rnrs base (6))
(for (top-level 0 ()) (meta 1)))
; This need not re-instantiate the previous top-level program as only
instantiation is necessary, and it has already been constructed. But:
> #!r6rs
(import (rnrs base (6))
(top-level 0 ())
(for (top-level 0 ()) (meta 1)))
OUTPUT: hi
; One additional instantiation is necessary in this case.
--
Brian Mastenbrook
[email protected]
http://brian.mastenbrook.net/
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