error:

Syntax:	error ( )
	error ( "error message" )

Description:

	The error function allows user-functions to jump back to the
	prompt when some sort of error has occurred. The nature of the
	error is up to the user. When an error is detected the user
	simply calls error(). If no argument is supplied, error() will
	print the default message. Otherwise, error prints the string
	supplied as an argument, and jumps back to the prompt.

	Jumping "back to the prompt" means execution of the current
	loop or function is terminated immediately and execution of
	any prompt-level statements is performed.
