throw

Help Contents Conditional execution throw
cond catch

throw tag
(throw tag value)

command. Must be used within the scope of a catch with an equal tag. Ends the running of the instructionlist of the CATCH. If THROW is used with only one input, the corresponding CATCH does not output a value. If THROW is used with two inputs, the second provides an output for the CATCH. 

	THROW "TOPLEVEL
can be used to terminate all running procedures and interactive pauses, and return to the toplevel instruction prompt. Typing the system interrupt character [Ctrl-Pause] has the same effect. 
	THROW "error
can be used to generate an error condition. If the error is not caught, it prints a message (THROW "ERROR) with the usual indication of where the error (in this case the THROW) occurred. If a second input is used along with a tag of ERROR, that second input is used as the text of the error message instead of the standard message. Also, in this case, the location indicated for the error will be not the location of the THROW, but the location where the procedure containing the THROW was invoked. This allows user-defined procedures to generate error messages as if they were primitives. Note: in this case the corresponding 
	CATCH "ERROR,
if any, does not output, since the second input to THROW is not considered a return value. 
	THROW "SYSTEM
immediately leaves Logo, returning to the operating system, without printing the usual parting message and without deleting any editor temporary file written by edit.

Example: 

to t
	catch "Hallo
	[	pr 1
		throw "Hallo
		pr 2
	]
	pr 3
end
;t defined
t
;1
;3

See also:

Examples:

References:

cond catch