Proposal: [252] Exclude zero from the data types that are identifiers

Author

Ruv

Change Log

• 2022-08-14 Initial version

Problem

In many cases it's supposed that a data object cannot be equal to a single-cell value zero, but the corresponding data type allows that.

For example

• NAME>INTERPRET implies that an execution token cannot be zero.
• FIND-NAME implies that a name token cannot be zero.
• Usual practice in programs is to assume an address, a file identifier, a word list identifier be a nonzero value.

Solution

Explicitly exclude zero from the address, execution token, name token, word list identifier, file identifier data types. When zero is a valid value on the underlying level, it can be reserved from use, or filtered out in the wrappers over the API routines of the underlying level.

Also, fix incorrect wording in the "subtype" definition, since members are not a subject of the subset relationship (it actually operates on sets):

"A data type i is a subtype of type j if and only if the members of i are a subset of the members of j".

Also, add the missed data type relationships.

Proposal

Fix wording for "subtype"

In the section 3.1.1 Data-type relationships

Replace the phrase:

A data type i is a subtype of type j if and only if the members of i are a subset of the members of j.

With the phrase:

A data type i is a subtype of type j if and only if each member of i is a members of j.

Notation for difference between sets (relative complement)

In the section 3.1.1 Data-type relationships, add the following phrase at the end of the first paragraph:

The notation "i \ j" is used to denote "the data type that includes all those and only those members of i which are not members of j".

Exclude zero from the address and execution token data types

In the section 3.1.1 Data-type relationships

Replace:

a-addr ? c-addr ? addr ? u ;

With:

a-addr ? c-addr ? addr ? u \ {0} ;

Replace:

xt ? x;

With:

xt ? x \ {0};

Exclude zero from the name token data type

In the end of the section 15.3.1 Data types add the following subsection:

15.3.1.1 Data-type relationships

Add the following to the end of the list of subtype relationships in the section 3.1.1 Data-type relationships:

nt ? x \ {0};

Exclude zero from the word list identifier data type

In the end of the section 16.3.1 Data types add the following subsection:

16.3.1.1 Data-type relationships

Add the following to the end of the list of subtype relationships in the section 3.1.1 Data-type relationships:

wid ? x \ {0};

Exclude zero from the file identifier data type

In the end of the section 11.3.1 Data types add the following subsection:

11.3.1.1 Data-type relationships

Add the following to the end of the list of subtype relationships in the section 3.1.1 Data-type relationships:

fam ? x;

fileid ? x \ {0};