Structural Delimiters


The only unusual aspect of MMT’s default concrete syntax is the use of the characters Unicode U+2758-A as structural delimiters. These are usually considered whitespace, and most fonts do not even have glyphs for them. Therefore, typing and displaying them depends on the editor and font used.

The advantage of these delimiters is that they do not clash with any other delimiters used by notations, lexing rules, or external formats that are integrated with MMT. Therefore, they permit near-perfect error recovery during parsing, orthogonality of language features, and combining different languages in the same file.

Every delimiter marks the end of a declaration or a component of a declaration.

Symbol in jEdit Delimiter Name in Unicode Marks end of Comment
GS U+275A Module Delimiter Modules any declaration that has nested declarations, i.e., theory, view, structure etc.
RS U+2759 Declaration Delimiter Declarations in particular includes and constants. Redundant if end of module follows
US U+2758 Object Delimiter Components of declarations in particular type, definiens, notation of a constant. Redundant if end of declaration follows.

Note that these form a hierarchy of nested levels and that we can think of SPACE as the 5th level delimiter, which marks the end of a keyword.

In jEdit

The jEdit plugin offers three ways to insert these non-standard symbols.

  • MMT adds buttons for all three delimiters to the toolbar of jEdit:

    menu

    • O inserts the object delimiter,
    • D inserts the declaration delimiter,
    • M inserts the module delimiter.
  • via the menu option Plugins > MMTPlugin > Insert <DELIMITER>
  • via the predefined abbreviations:
    • jOD for the object delimiter,
    • jDD for the declaration delimiter,
    • jMD for the module delimiter.

You can modify (or add new) abbreviations in Extras > Global Options > Abbreviations.