Change History

Version 0.996.0, September 2024

Text syntax:

• Switch from |…| to '…' quotation of Symbols. The syntax with pipes originated with Racket and other Schemes and Lisps, but is unusual outside the Lisp world. The syntax with single-quotes lines up with languages like Smalltalk, Erlang, Prolog and Ruby.

Version 0.995.0, May 2024

Text syntax:

• Support Unix interpreter specification (#!) lines, reading them as annotations.

Schema:

• Document pattern extensibility: essentially, prefix-matching of sequence-like Values.

Version 0.994.0, March 2024

Overall:

• Remove Float, leaving Double as the sole supported kind of IEEE 754 floating-point number.

Binary syntax:

• Remove 0x87 0x04 syntax for Floats.

Text syntax:

• Switch #! to #: as the prefix for Embedded values.
• Remove trailing-f syntax for Floats.

Schema:

• Clarify the idea of “sufficiently identifierlike” values.
• Give a schema, host.prs, describing host-language types abstractly.

P-expressions:

• Introduce Trailers, for annotations at the end of a block.

Version 0.992.0, November 2023

Text syntax:

• Remove commas from whitespace. Instead, explicitly ignore them inside Sequences, Sets, and Dictionarys.

Version 0.991.0, October 2023

Overall:

• Introduce P-expressions.
• Clarify the meaning of lexicographical comparison in Preserves.

Text syntax:

• Use # instead of ; to mark line comments.

Version 0.990.1, October 2023

Overall:

• Repair examples of binary encoding to actually match the current specification.

Text syntax:

• Introduce the notion of “delimiters”.
• Make use of standard EBNF definitions like DQUOTE, ALPHA and DIGIT.

Schema:

• Relax the placement of / in OrPatterns to match the actual implementations.
• Relax the placement of & in AndPatterns to match the actual implementations.

Version 0.990.0, October 2023

Overall:

• Include “cheat sheet” quick-reference cards for Preserves syntax.

Binary syntax:

• Remove 0xA0-0xAF and 0x90-0x9F tags, which were used for various compact representations of SignedIntegers. Now, all integers use tag 0xB0.
• Switch from tags 0x82 and 0x83 for Float and Double, respectively, to tag 0x87 plus a length in bytes for both.

Version 0.7.1, October 2023

Overall:

• Update metaconventions and examples in conventions.md
• Make clear throughout that Preserves works with Unicode scalars, not code points.
• Clarify that unpaired surrogate code points are not permitted in strings and symbols.

Model:

• Add note regarding JSON compatibility and unpaired surrogate code points.
• Add appendix describing the “merge” of two Values.

Text syntax:

• Include recommendation for implementations to print sets and dictionaries in Preserves-ordering.
• Include recommendation that URL-safe base64 should be emitted by default.

Version 0.6.4, February 2023

Text syntax:

• Alter parsing of numbers and symbols to use SymbolOrNumber plus a disambiguation step.

Schema:

• Place “smaller” definitions first in alternations. For example, EmbeddedTypeName now has the #f branch first, rather than the Ref branch.

Version 0.6.3, June 2022

Overall:

• Split monolithic specification document into smaller, more focussed pieces.

Model:

• Clarify that NUL characters (code point zero) are permitted in strings and symbols.

Text syntax:

• Clarify that annotations on a value are ordered.

Schema:

• Include descriptions of host-language types.
• Include the beginnings of semantics.