STACK

$D\ X\ --$

DESCRIPTION

The switch operator uses X as a key to look up a value in dictionary D.

If X is found, its associated value is executed.
If X is not found but D has a null key, the value of the null key is executed.
If neither X nor a null key exists in D, the operator does nothing.

Key comparisons use the eq operator, so keys must be primitive (non-composite) objects. Values in D can be of any type (e.g., procedures, numbers, or arrays), and will be executed or returned accordingly.

ORIGIN

Procedure from boot.leo registered in systemdict.