2.3.12 If

An IF statement has the form:

    IF    B_1 THEN S_1
    ELSIF B_2 THEN S_2
      ...
    ELSIF B_n THEN S_n
    ELSE S_0
    END

where the B's are boolean expressions and the S's are statements. The ``ELSE S_0'' and each ``ELSIF B_$i$ THEN S_$i$'' are optional.

The statement evaluates the B's in order until some B_$i$ evaluates to TRUE, and then executes S_$i$. If none of the expressions evaluates to TRUE and ``ELSE S_0'' is present, S_0 is executed. If none of the expressions evaluates to TRUE and ``ELSE S_0'' is absent, the statement is a no-op (except for any side-effects of the B's).