TOPS-20 PASCAL Language Manual - Bitsavers

ISO COMPLIANCE
2. The concept of a "totally-undefined" variable has no meaning
in PASCAL-20. Any violation of the standard which requires
"totally-undefined" to be meaningful is not detected.
3. Variant records in PASCAL-20 are implemented by overlaying
the fields of the variants in the same memory. Changing the
active variant does not alter the contents of that memory,
and the fields of the newly-active variant are not undefined.
Also, note that variant parts of records cannot be of the
type FILE.
4. The DISPOSE procedure does not cause its argument to become
undefined, but rather the argument is set to NIL.
5. No restrictions on the relative placement of labels and GOTO
statements are enforced.
6. Packed and unpacked sets are implemented in similar ways in
PASCAL-20. Therefore, the compiler is very "loose" about
interchanging packed and unpacked sets; the only requirement
imposed on compatibility of set types is that their base
types must be compatible.
7. Under certain conditions, a procedure call may be bound to
the wrong procedure definition. This can only happen when
two procedures are declared with the same name at different
levels, and the inner procedure is called before it is
declared. The following example illustrates this situation.
PROCEDURE B;
BEGIN (* level 1 *)
END;
PROCEDURE C;
PROCEDURE D;
BEGIN
B (* call bound to level 1 procedure *)
END;
PROCEDURE B;
BEGIN (* level 2 *)
END;
BEGIN
END;
PASCAL-20 also imposes a number of restrictions on
are:
programs.
These
1. Identifiers may be of any length, but only the first 31
characters are stored. Therefore identifiers in PASCAL-20
must be unique in the first 31 characters.
2. The ordinal values of the base type of a set type are limited
to the range 0 •• 255. This means that no set may have more
than 256 elements.
3. File variables are not permitted as fields in the variant
part of a record.
4. The range of ordinal values of case constants in a CASE
statement must be less than 1000.
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