Changes included in SRC Technical Note 1997-005b

The following list reflects the complete set of changes made to SRC Technical Note 1997-005a to produce the revised note 1997-005b.

• The keyword include is changed to import. The old keyword had a misleading connotation of textual macro inclusion.

• The syntax of list constructors is changed to use angle brackets instead of square brackets. This syntax creates a minor ambiguity in the grammar; a new section explains how the ambiguity is resolved.

• The types t_nil, t_binding_ne, and t_list_ne are eliminated. Empty list and empty binding are now distinct values of type t_list and t_binding. This change was made possible by the change to list syntax, which creates a syntactic distinction between empty list and empty binding that was previously lacking.

• The syntactic sugar [ = Id ] for the binding constructor [ Id = Id ] is removed. New syntactic sugar [ Id ] for [ Id = Id ] replaces it. This change makes the binding syntax used in the body of a model more consistent with that used in the files and import clauses. It was made possible by the change to list syntax; formerly [ Id ] denoted a list.

• The desugaring of [ GenArc Delim = Id ] to [ GenArc = [ Id = Id ] ] is removed. A new desugaring of [ GenArc Delim = Expr ] to [ GenArc = Expr ] replaces it. This change removes an apparently useless feature and gives meaning to certain expressions that were formerly syntactically legal but semantically undefined.

• The definition of the identifier token is more liberal; an identifier token may now begin with a digit, as long as it does not match the pattern for an integer token. This change removes the need for extra quotation marks in certain common cases, such as when a model is being imported from a branch.

• Octal constants are now permitted.

• The description of tokenization is more precise.

• The meaning of an Arc nonterminal that matches an Integer token is clarified.

• The Files and Imports clauses now accept a general Arc on the left-hand side of an equal sign, but a new semantic rule forbids defining a top-level name that is not a legal identifier. This clears up some poorly defined cases and disagreements between the spec and the implementation.

• Special cases in the translation of DelimPaths to filenames are corrected and clarified.

• The _par_map primitive is added.

• The type syntax is changed to use parentheses uniformly instead of using square brackets for lists and bindings.

• Some minor typos and wording errors are corrected.