A SWITCH statement has the form
SWITCH alt-0, {alt-1, alt-2, alt-3...}
and MUST be labelled with a statement number.
Only statement numbers, not statements in braces, may appear as alternates in this statement.
This statement performs a function similar to that of the JUMP statement, or the assigned GO TO in FORTRAN. Instead of requiring a variable to be initialized, however, alt-0 constitutes the initial value associated with the statement itself that serves as its branch destination.
This value is subject to change by the ALTER_SWITCH statment. The list of destinations alt-1, alt-2, alt-3... contains all the values to which that value is allowed to be changed. The statement can be considered as analogous to a switch on a railroad track, which may be changed remotely to divert flow to another direction.