Tertiaries are formulæ and NIL
.
Formulæ were covered in chapter two. All that
needs to be said here is that a formula can consist solely of a single
secondary or primary or enclosed
clause although this is not usual. If a formula, containing at least
one operator, is to be used as a primary or a secondary, it must be
enclosed in parentheses (or BEGIN
and END
).
For example, in the formula next OF (H declarer)
, where
H = (INT)REF HAND
and HAND = STRUCT(...,REF HAND
next)
, the formula must be surrounded by parentheses to make it
into a secondary.
The only name having a denotation is NIL
. Its mode is
REF
whatever
. In other words, it can have
any mode which starts with REF
. It does not refer to any
value and, although it must only occur in a strong context, it cannot
be coerced. Its uses are described in the next chapter.