Mikael Djurfeldt <mik...@djurfeldt.com> writes:
> The interface of (value-history) would instead have a lazy-binder
> which provides a syntax transformer for every $... actually being
> used. The $... identifier would expand into a list-ref into the value
> history.
A few more suggestions:
If I write (define (foo x) (+ $$0 x)) at the repl, then I expect 'foo'
to continue to refer to the same entry in the value history, even after
the value history is later extended.
I'm also a bit concerned about the efficiency implications of expanding
these variable references into 'list-ref' calls when the history grows
large. If I write a loop that evaluates $$0 a million times, I'd prefer
to avoid a million 'list-ref' calls.
To address these concerns, I'd like to suggest a slightly different
approach:
* $0, $1, ... would continue to be ordinary variable bindings in
(value-history), as they are now.
* The 'count' in 'save-value-history' would be made into a top-level
variable in (ice-9 history).
* $$0, $$1, $$2, ... would be handled by a lazy-binder, providing a
syntax transformer that looks at the value of 'count' at macro
expansion time, and expands into the appropriate variable
reference $N.
For example, if $5 is the most recent value, $$0 would expand into $5
instead of (list-ref ...). This would eliminate my concerns over
efficiency.
What do you think?
Mark
