Transactions

Each line you type runs as a transaction on your tab's world. Either all of it happens or none of it does.

1 2 3
[ 7 ] :seven 4 5 0 /

The division fails, so seven is not defined, 4 5 is not pushed, and the stack is still 1 2 3.

Scope

Transactions only cover the tab's stack and definitions. These are outside them:

• Printed text, which stays on screen.
• Root, whose edits are rebuilt with their own all-or-nothing rule (root).
• The machine. Memory, ports, alloc and direct screen writes take effect when the word runs (omega for smarties).
• The disk, which is only written after a line succeeds.

Lines that change nothing

A line that leaves the stack and definitions unchanged, such as words or "hi" say, is not recorded or saved, and back skips over it.

Continuing after a failure

try lets a line continue past a failing quote. Catching describes what survives.

Faults

A CPU fault restarts the tab, prints the fault and reports your last line was dropped. The world is unaffected, since the line never committed.

How worlds work describes the commit in detail.