====== ON ======

Syntax:

  on <byte or int index> goto label [ ,label ...]

or:

  on <byte or int index> gosub label [ ,label ...]
  
The ''ON'' language construct creates a conditional branch that accepts an //index// and a list of labels. The expression //index// will be evaluated and the corresponding label from the list will be passed to ''GOTO'' or ''GOSUB''.

If //index// is an integer, it will be implicitly truncated to a byte. The maximum number of labels in the list is therefore 256.

**Note #1:** The list of labels is zero-indexed, which means that if //index// evaluates to 0, the first label will be matched, if it evaluates to 1, the second, etc..

**Note #2:** The runtime will not check if //index// is within the number of labels. If //index// is larger than the number of labels minus one, the program will (most probably) break.

Example:

  rem -- i! holds a value between 0 and 2 
  on i! goto case0, case1, case2
  end
  case0:
    print "i! equals 0"
    end
  case1:
    print "i! equals 1"
    end
  case2:
    print "i! equals 2"
    end
    
====== Performance tip ======

An ''ON ... GOTO'' or ''ON ... GOSUB'' construct is faster than its ''IF ... THEN GOTO/GOSUB'' equivalent. It's especially useful when branching on a TRUE/FALSE condition, for example:

  rem -- branching using IF ... THEN
  rem -- assume x! is a zero or one (TRUE/FALSE) value
  
  if x! = 0 then goto false_case else goto true_case
  
  rem -- same as above but FASTER
  
  on x! goto false_case, true_case