Rosie Pattern Language: Near-term Roadmap

Rosie v1.0.0 is in alpha release now. Our intention is to release a beta version in early 2018, with a frozen feature set, API, CLI, and REPL interfaces. The beta will be a release candidate for the proper version 1.0.0.

Over the course of the alpha releases, we have been adding features and making minor changes. Three important features will be added before the beta: thread safety; unicode predicates; and enhanced customization.

Thread safety

Note (edit): Thread safety arrived in librosie in v1.0.0-alpha-7. See src/librosie/C/mt.c for an example of a multi-threaded Rosie program.

The librosie in v1.0.0-alpha-6 (and earlier) is not thread-safe. Some changes to the API and to the compilation of the library will make it safe for multi-threading. An enforced limitation is that a matching engine may be used by only one thread at a time. In other words, for parallel execution, you must create a matching engine for each thread. Fortunately, matching engines are fairly lightweight.

Unicode predicates

Rosie v1.0.0 has a powerful feature for defining character sets, but the alpha releases (thus far) lack support for Unicode predicates like “characters in the Hebrew script”; or “one of the nearly 1000 characters labeled as Numeric” in Unicode 10.0.0; or the intersection, union, or difference of these.

An upcoming alpha release will add predicates for Unicode scripts and properties.

Rosie supports only the UTF-8 character encoding today. No requests for other encodings have been received, but we are interested to know if the need exists.

Note (edit): [2018-01-08] We posted today on the design of character sets in RPL.

Customization, and the Rosie Prelude

Rosie is often used from the command line, and a common request is for Rosie to load an initialization file (e.g. ~/.rosierc) so that frequently used options can be specified there.

Another command-line customization is the ability to assign colors (for printing matches in colorized text) to patterns. This feature is also forthcoming.

And, in some installations, a user of the CLI, REPL, or API may want to have some patterns pre-loaded automatically. This customization is likely to take the form of import statements listed in an initialization file.

Finally, some users may wish to customize the Rosie Prelude¹, i.e. the set of patterns and functions/macros that form the base set on top of which other patterns are built. Rosie patterns like . (dot, matching any character), $ (dollar, matching end of input), and ^ (caret, matching start of input) are among the identifiers present in the Prelude.

The Rosie . matches any UTF-8 encoded character. Some users may wish to redefine . to match any ASCII character instead, as part of an ASCII-only configuration.

Similarly, the Rosie boundary pattern (bound to the tilde symbol, ~) is defined to match a variety of word and other boundaries. To customize the boundary for all imported packages and all loaded RPL files, the definition must be modified in the Prelude.

Note: A redefinition of ~ in an ordinary (non-Prelude) RPL file will affect all of the patterns defined in that file, but not any outside of that file.

Since pattern libraries are compiled in the environment of the Prelude, modifications to the Prelude will affect all patterns subsequently loaded (imported, compiled), and this can break RPL packages which depend in some way on the standard Rosie Prelude. The ability to use a custom Prelude is intended for specialized use cases, and also to allow the Rosie user community to evolve Rosie independently of official releases.

[1] The name prelude was borrowed from the Haskell language, where (to my understanding) the Haskell Prelude serves a similar function:

Prelude is a module that contains a small set of standard definitions and is included automatically into all Haskell modules.

Rosie was created for scalable pattern matching

Rosie was created to address pattern matching in the large: big data; great variety of data formats; many patterns; and many developers.

Thread safety is a therefore requirement. Also, the world of data and programmers and projects is much larger than the United States, and includes so many languages beyond English. Thus, Unicode character predicates are a requirement. Finally, the CLI and REPL are not only an easy way to get started with Rosie – they are, for many users, the primary way of running Rosie. So, the ability to customize the user experience is also a requirement. These requirements will be addressed in the near-term roadmap.

Pattern matching in the large is #modernpatternmatching.

Please contribute discussion and questions to the Rosie subreddit.