decr/2 and prev/2—return an integer or enumeration slot value decremented by 1

The decr/2 and prev/2 operations return an integer or enumeration slot value decremented by 1. 

The syntax for decr/2 operation is as follows:

$VAL=decr($SLOT)

decr/2 arguments

Use decr/2 to retrieve the value of the slot referenced in $SLOT decremented by 1 in $VAL. For an enumeration, the slot value returned is decremented to the next lower value. If there is no lower value, the slot value returned remains unmodified.

The referenced slot itself is not modified.

decr/2 example

$NEWPRIO = decr( $E.mc_priority );