single-form-form-parser is a predefined form parser for use with define-form-parser. The parser consumes one subform and returns a dspec made from the defining form and the subform. This can be used in the common case where a defining form has a name that follows the defining macro and the dspec class is the same as the defining macro, for example defclass.
single-form-form-parser is the predefined parser for
define-method-combination top level forms. It is also the parser for various LispWorks extensions such as defsystem.
You can define it to be the parser for your defining forms. using define-form-parser.
LispWorks User Guide and Reference Manual - 20 Sep 2017