block_bind_incremental is block_bind_referenced in a loop backwards. For
an 1-inst block, it does the same thing and isn't too much more
expensive, so it's not really useful to keep both.
Also, block_bind_referenced was a better name for the function.
Since 605bfb3, block_drop_unreferenced actually reverses the order of
instructions in the block it's run against. This bug was hidden by the
fact that normally it's run *twice* against the main program, flipping
it back, and that order of function definitionss doesn't really matter
after symbol resolution.
Avoid doing the internal binding of top-level symbols in the parser,
leaving that work to be done in a post-processing step. For builtins,
this lets us do a reference-aware bind step (block_bind_incremental)
*after* generating builtins/0.
Libraries are a bit trickier since they may be bound multiple times, so
instead of thinking through the implications I added (block_bind_self)
to resolve all internal symbols immediately.
Attempting to use the existing FORK_OPT opcode resulted in difficulty
knowing when to pop an error message off the stack and when not to. This
commit makes DESTRUCTURE_ALT a real opcode that is identical to
FORK_OPT, except for never pushing the error message onto the stack when
continuing from an error backtrack.
Some small changes were necessary to the DUP/POP behavior surrounding
destructuring to accomodate this.
This reverts commit e24af3c78e.
While the semantics are desirable, there is no way to implement them
efficiently. The reason is that in order to handle backtracking (empty)
from the state update expression, we have to retain a reference to the
reduction state value in order to restore it upon backtracking.
Retaining a reference to the reduction state kills performance by
causing lots of additional memory allocations and garbage because the
input to the update expression will always have at least two references,
thus no changes to it can be done in-place, and all changes end up being
CoW changes.
Avoiding this is the very reason for the LOADVN instruction (leaving
`null` in the variable loaded from).
The conditional expression in if-then-elif-else-end cannot contribute to
path expressions because it doesn't change the input to any of the then/
elif/else expressions. These must be generated via gen_subexp().
See also #1366.
Muh Muhten