A CASE statement has the form:
CASE Expr OF
L_1 => S_1
| ...
| L_n => S_n
ELSE S_0
END
where Expr is an expression whose type is an ordinal type and
each L is a list of constant expressions or ranges of constant
expressions denoted by "e_1..e_2", which represent
the values from e_1 to e_2 inclusive. If
e_1 exceeds e_2, the range is empty. It is a static
error if the sets represented by any two L's overlap or if
the value of any of the constant expressions is not a member of the
type of Expr. The "ELSE S_0" is optional.
The statement evaluates Expr. If the resulting value is in any L_i, then S_i is executed. If the value is in no L_i and "ELSE S_0" is present, then it is executed. If the value is in no L_i and "ELSE S_0" is absent, a checked runtime error occurs.