5.8 Extension of a Formalism

The definition of operators or phyla can reuse some phyla previously defined in another formalism.

It is also possible to extend a formalism by adding to a previous definition some new operators and new phyla. The result is a new formalism (there is no reuse in this case) strongly related to the previous one as it is possible to coerce programs from the old formalism into programs in the new one. The reverse can only be done if the operators that have been added are not used.

program     -->   "abstract" "syntax" "of" id 
                     "extends" id "with" declaration*
                  "end" [id] ";"

Only formalisms defined with AS can be extended.