To describe the PL/I language, the following conventions
are used:
- The descriptions are informal. For example, we usually write "x
must be a variable" instead of the more precise "x must be
the name of a variable". Similarly, we can sometimes write "x
is transmitted" instead of "the value of x is transmitted". When
the syntax indicates "reference", we can later write "the
variable" instead of "the referenced variable".
- When we say that two different source constructs are equivalent,
we mean that they produce the same result, and not necessarily that
the implementation is the same.
- Unless specifically stated in the text following the syntax
specification, the unqualified term "expression" or "reference" refers
to a scalar expression. For an expression other than a scalar expression,
the type of expression is noted. For example, the term "array
expression" indicates that neither a scalar expression nor a
structure expression is valid.
- When a result or behavior is undefined,
it is something you "must not" do. Use of an undefined feature
is likely to produce different results on different implementations
or releases of a PL/I product. The application program is considered
to be in error.
- Default is used to describe an alternative
value, attribute, or option that is assumed by the system when no
explicit choice is specified.
- Implicit is used to describe the action
taken in the absence of an explicit specification by the program.
- The lowercase letter b, when not in a word, indicates a blank
character.
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