select on a value

select on <value> dispatches to the arm whose when matches the value, and runs nothing if none do. The classic use is a state machine: one arm per declared state, each speaking for that state.

  on examining it
    select on its state
      when dormant
        phrase bulb-dormant
      when sprouting
        phrase bulb-sprouting
      when blooming
        phrase bulb-blooming
    end select
  end on

The value after on is any value expression: here its state, the amaryllis bulb's current state out of dormant, sprouting, blooming. Each when <word> heads an arm whose body is ordinary statements. The block closes with end select, and each or-free arm simply dedents. Coverage is not enforced: an unmatched value falls through silently, which is what you want for "react only to these states."

Do not confuse this arm-header when <word> with the statement-final when <condition> suffix. Same word, different job: the suffix gates one statement on a condition, while the arm header names a value to match. select on compares values; it does not evaluate conditions.