If you cast your mind back to the form of an Algol 68 program,
you will remember that it consists of a number of phrases enclosed by
BEGIN
and END
(or parentheses) preceded by a
PROGRAM phrase with an optional
USE phrase. The part of the program
enclosed by BEGIN
and END
(including the
BEGIN
and END
) is called a closed
clause. The important point here is that a
closed clause consists of one or more phrases separated by
semicolons; (the last
phrase being a unit), surrounded
by parentheses (or BEGIN
and END
). Since a
declaration is not a unit, the last phrase cannot be a declaration.
We say that the value of a closed clause is the
value yielded by the final unit. As an example, here is a closed
clause with a value of mode INT
:
BEGIN INT i = 43; print((i,newline)); i END
An important adjunct of a closed clause is that any identifiers declared in the clause do not exist outside the clause. We say that the range of an identifier is confined to that section of the closed clause from its declaration to the end of the clause.
Sian Mountbatten 2012-01-19