Hello,
Sometimes your hacking data at the REPL and get the live system in a
state that takes alot of work to reproduce. It would be nice if the user
could "rewind" back to any previous state of the repl; this state would
include the global environment. Instead of just rewinding, in a
graphical environment it would be nice to select a repl state and open a
new graphical repl from that point. This is what I mean by "branchable
repl".
This is not science fiction; I've hacked up such an environment before.
Continuations in the Factor programming language contain 5 stacks:
datastack callstack retainstack namestack catchstack
The 'datastack' the stack where you manipulate your data. The
'namestack' can be thought of as the environment. My hack involved
tweaking graphical repl; each prompt was actually a button. This button
was a closure with a pointer to the corresponding "current
continuation". So you could scroll back in the repl history, click any
prompt, and get a new repl starting at that state.
A drawback with such a system is the increased memory usage. It would be
nice if the system would discard the oldest objects referenced in the
repl on an as needed basis; i.e. as you cross some memory threshold.
Ed
