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SIGNAL
usage: SIGNAL {ON|OFF} condition
or: SIGNAL [value] expression

1)first form controls the state of the internal interrupt flags. Must be followed by ON or OFF keywords, and one of the condition keywords listed below:

BREAK_C - a control-C was detected
BREAK_D - a control-D was detected
BREAK_E - a control-E was detected
BREAK_F - a control-F was detected
ERROR - a host command returned a non-zero code
HALT - an external HALT request was detected
IOERR - an error was detected by the I/O system
NOVALUE - an uninitialized variable was used
SYNTAX - a syntax or execution error was detected

2)SIGNAL [value] expression
An immediate interrupt is generated that transfers control to the label specified by the expression result. The instruction thus acts as a "computed goto".

-see also INTERRUPTS for other info and special variables