6.1.4.4 The *commands* Table

The table *commands* in an enhanced relational-database has the fields (with domains):

PRI name        symbol
    parameters  parameter-list
    procedure   expression
    documentation string

The parameters field is a foreign key (domain parameter-list) of the *catalog-data* table and should have the value of a table described by *parameter-columns*. This parameter-list table describes the arguments suitable for passing to the associated command. The intent of this table is to be of a form such that different user-interfaces (for instance, pull-down menus or plain-text queries) can operate from the same table. A parameter-list table has the following fields:

PRI index       ordinal
    name        symbol
    arity       parameter-arity
    domain      domain
    defaulter   expression
    expander    expression
    documentation string

The arity field can take the values:

single

Requires a single parameter of the specified domain.

optional

A single parameter of the specified domain or zero parameters is acceptable.

boolean

A single boolean parameter or zero parameters (in which case #f is substituted) is acceptable.

nary

Any number of parameters of the specified domain are acceptable. The argument passed to the command function is always a list of the parameters.

nary1

One or more of parameters of the specified domain are acceptable. The argument passed to the command function is always a list of the parameters.

The domain field specifies the domain which a parameter or parameters in the indexth field must satisfy.

The defaulter field is an expression whose value is either #f or a procedure of one argument (the parameter-list) which returns a list of the default value or values as appropriate. Note that since the defaulter procedure is called every time a default parameter is needed for this column, sticky defaults can be implemented using shared state with the domain-integrity-rule.