CONSTRAINT ATTRIBUTES

Constraint attributes can be associated with deftemplate and defclass slots so that type checking can be performed on slot values when template facts and instances are created. The constraint information is also analyzed for the patterns on the LHS of a rule to determine if the specified constraints prevent the rule from ever firing.

The syntax for constraint attributes is:

<constraint-attribute> ::= <type-attribute> |
                           <allowed-constant-attribute> |
                           <range-attribute> |
                           <cardinality-attribute>
                           <default-attribute>

<type-attribute>       ::= (type <type-specification>)

<type-specification>   ::= <allowed-type>+ | ?VARIABLE

<allowed-type>         ::= SYMBOL | STRING | LEXEME |
                           INTEGER | FLOAT | NUMBER | 
                           INSTANCE-NAME | INSTANCE-ADDRESS |
                           INSTANCE |
                           EXTERNAL-ADDRESS | FACT-ADDRESS

<allowed-constant-attribute> 
                       ::= (allowedsymbols <symbol-list>) |
                           (allowedstrings <string-list>) |
                           (allowed-lexemes <lexeme-list> |
                           (allowedintegers <integer-list>) |
                           (allowedfloats <float-list>) |
                           (allowednumbers <number-list>) |
                           (allowed-instance-names <instance-list>) |
                           (allowedvalues <value-list>) |

<symbol-list>          ::= <symbol>+ | ?VARIABLE

<string-list>          ::= <string>+ | ?VARIABLE

<lexeme-list>          ::= <lexeme>+ | ?VARIABLE

<integer-list>         ::= <integer>+ | ?VARIABLE

<float-list>           ::= <float>+ | ?VARIABLE

<number-list>          ::= <number>+ | ?VARIABLE

<instance-name-list>   ::= <instance-name>+ | ?VARIABLE

<value-list>           ::= <constant>+ | ?VARIABLE

<range-attribute>      ::= (range <range-specification> 
                                  <range-specification>)

<range-specification>  ::= <number> | ?VARIABLE

<cardinality-attribute>    
                    ::= (cardinality <cardinality-specification> 
                                     <cardinality-specification>)

<cardinality-specification> ::= <integer> | ?VARIABLE