nickel/RELEASES.md

Version 0.2 (2022-07-29)

Breaking changes

• Using a contract as part of a static type annotation will in most cases fail with an appropriate error message. This is a temporary limitation in order to fix previously unsound behavior in the typechecker. This restriction will likely be lifted in the upcoming 0.3.x release. For more details, see issues #701 and #724

Fixes

• Fix unnecessarily restricted record contract for record.update
• Fix wrong interpretation of long interpolation-like sequences %..%{ in strings
• Fix panic when evaluating a switch in specific cases
• Fix fields without definition being assigned to null, instead of just being marked as undefined

Language features

• Merging null values together gives null, and merging empty lists together gives an empty list, instead of failing with error: non mergeable terms
• Add recursive let-bindings (let rec)
• Add type wildcards. Use _ in place of a type to let the typechecker fill the gap. Example: let foo : _ = array.all ((==) 2) [1,2,3]
• Add builtin.to_str and string.from to convert generic values to a string
• Re-introduce an official syntax for enum types

Tooling

• Add the nickel pprint-ast command to pretty print a parsed program (mostly debugging purpose)
• Add the nickel doc command to produce markdown documentation from the in-code doc metadata

Documentation

• Fix various typos and remove use of deprecated syntax in the user manual

Version 0.1 (2022-03-10)

First release! The main focus has been the design of the Nickel language itself.

Language features

• Gradual type system with row types, polymorphism and type inference
• Contract system for data validation
• Merge system for recursive records that supports one level of overriding
• Metadata annotations (default values, documentation, etc.)
• Unified syntax for terms, types and contracts (RFC002)
• Record destructuring

Tooling

• The main binary supports the following subcommands:

  • nickel query to show metadata and documentation of library functions, the field of a configuration, etc.
  • nickel export to serialize to JSON, YAML, or TOML
  • nickel repl to launch an REPL
  • nickel typecheck to do typechecking without evaluating

• An LSP-server is included

Documentation

• User manual sections on syntax, correctness (types and contracts), and merging
• The standard library has been documented in-code (use nickel query/:query to retrieve it)

Known limitations

• The roadmap for overriding and the merge system (RFC001) has not been implemented fully yet.

• Performance has not been prioritized.

• Due to the use of reference counting as a memory management strategy, mutually recursive record fields are currently leaking memory. This shouldn't be an issue in a standard workflow.

• Standard library APIs and language features are subject to change. There is no backward compatibility guarantees for this version. In general, this release is meant for experimenting and getting user feedback, but isn't intended to be used in production.