Catching

try runs a quote and keeps a failure inside it from aborting the line. It leaves 1 if the quote completed, or prints the error and leaves 0 if it failed.

[ 1 0 / ] try .         prints the error, then 0

No rollback

try doesn't roll anything back:

[ 5 6 0 / ] try

leaves 5 0. The 5 was pushed before the failure and stays, and the 0 comes from try. Only the line as a whole is a transaction.

Restoring the stack after a failure is up to you. learn does it by saving the stack with depth list before each line and spreading it back when try leaves 0 ('learn open).

Interrupts

Ctrl-C raises interrupted, which is an ordinary error, so try catches it:

[ 1000000000 [ ] times ] try "after" say

Pressing Ctrl-C there prints ! interrupted and then after. The stopped error from trace is caught the same way.

Limits

try can't catch a CPU fault, which restarts the tab, or halt.

Use

Use try for failures you expect:

"12x" [ >num ] try [ "number" say ] [ "not a number" say ] if

Wrapping code in try defensively makes failures harder to find, since a line that fails outright is easier to debug than one that continues with a damaged stack. The messages are listed in errors.