Appendix C: Changes from the Tentative Design

Only the major changes are listed. All significant changes to the abstract syntax of CASL are marked with a `!' on the left.

• Carrier sets are now always non-empty.
• The notion of explicitly-sorted term has been eliminated.
• Redeclaration of the same symbol is now allowed, both in lists of basic items and in extensions.
• The same identifier may be used simultaneously to name several different kinds of entities, e.g., a sort and a function.
• Visibility is now non-linear in lists of basic items.
• Type definition groups have been eliminated from structured specifications, and type definitions (now called datatype declarations) as basic items no longer involve free extensions.
• Multiple selectors of the same sort now have to be specified separately.
• Attributions are now included.
• Constants can now be used without an application.
• The syntax of EXTENSION has been simplified, and analogously in generic specifications.
• Local specifications have been introduced.
• Different syntactic categories for specification names have been introduced.
• Subsort embeddings between component sorts no longer induce the same between compound sort identifiers.
• Architectural specifications can be referred to from ordinary specifications.
• Unit definitions have been introduced.